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Preliminary Chemistry Topic 2 “Metals”Copyright © 2005-22009 keep it simple sciencewww.keepitsimplescience.com.au

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but first, an introduction...

Preliminary Chemistry Topic 2

METALSWhat is this topic about?To keep it as simple as possible, (K.I.S.S.) this topic involves the study of:1. OUR USE of METALS

2. CHEMICAL ACTIVITY of the METALS3. PATTERNS of the PERIODIC TABLE

4. QUANTITY CALCULATIONS... the MOLE5. METALS from their ORES

...all in the context of how Chemistry contributes to cultural development

Technology Needs MetalsThe great sweep of human cultural developmenthas many aspects... Language, Religion, Art &Music, and, of course, Technology.

The history of technology is closely linked withour use of metals; in fact historians have namedsome parts of history after the metals thatchanged the way people lived.

Chemistry of the MetalsIn the previous topic you learnt about theElements of the Periodic Table. In this topic youwill concentrate on the chemistry of the metals,and some of the chemical patterns that theyshow.... and Speaking of Patterns,

in this topic you will find that

The Periodic Table

is full of patterns

Measuring Chemical QuantitiesIn this topic you will also be introduced to theconcept of the “Mole”...

not a burrowing mammal!not a traitor within the group!not a gangster’s girlfriend!certainly not a skin blemish!

A Chemical Mole is a clever way to measurequantities; essential for analysis & chemicalmanufacture.

This topic starts with a quick look at the historyof metal use, and ends with a study of how weget metals from the Earth, and the chemistry ofthe extraction process.

Electrically powered smelter plant for extracting

Aluminium from its ore

Photo courtesy of Comalco Aluminium Ltd

Metals

Non-MMetals

If you know the mass, you can figure out

how many atoms there are... thanks to the mole.

Dagger from the “Bronze Age”




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MineralsOres

&Resources

MetalsWe UseToday

History of Metal Use

Definition of theMole.

Avogadro’sNumber

Activity & Usageof Metals

Electron TransferREDOX

The Case forRecycling Metals

Case Study:Extracting

Copperfrom its Ore

Mole QuantityCalculations

Molar Ratios in Reactions

History of the Periodic Table

1st IonisationEnergy

Gay-Lussac’s Law&

Avogadro’s Hypothesis

EmpiricalFormulas

The Activity Seriesof the Metals

METALS

Our Use ofMetals Chemical Activity

of the Metals

Patterns of thePeriodic Table

QuantityCalculations

the MoleExtracting Metals

from Ores

CONCEPT DIAGRAM (“Mind Map”) OF TOPICSome students find that memorising the OUTLINE of a topic helps them learn and remember

the concepts and important facts. As you proceed through the topic, come back to this page regularly to see how each bit fits the whole.

At the end of the notes you will find a blank version of this “Mind Map” to practise on.


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1. OUR USE OF METALSkeep it simple science

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Human Progress has always been linkedto our use of Metals.

Progress in metal usage has always beenlinked to the availability of energy

to extract the metals.

The First Uses of MetalsFor most of human existence, people used tools ofstone, wood and bone. Primitive tribes were familiarwith gold which occurs uncombined in nature, but it istoo soft to be useful for anything but jewellery anddecoration.

About 5,000 years ago, in the Middle East, somepeople accidentally discovered that if certain rockswere roasted by fire, small amounts of copperwould be found later in the ashes. Copper is toosoft to be really useful, but there was a brief“Copper Age” around the eastern end of theMediterranean Sea. Copper was used fordecoration, jewellery, small utensils, andoccasionally for knives and spear points.

The big breakthrough was the discovery by thesecopper-using people that if they roasted copper-bearing rocks (ores) with tin ores, the resulting“alloy” (mixture) of copper and tin produced amuch harder metal, “bronze”, which could be castin moulds, and hammered to shape many usefultools and weapons.

The Bronze Age (approx 4,500 to 2,500 years ago)It is no accident that the rise of the greatancient civilizations occurred about thistime. The stone blocks of the pyramids andtemples of ancient Egypt were cut and shapedwith bronze chisels. Egyptians, and laterGreeks, dominated their world because theirsoldiers were armed with bronze swords,spears and arrowheads.With bronze tools they built better ships and wagons fortransport and trade, which brought wealth and power.

Sad as it might be, thefacts of human historyare that progress hasbeen marked by conflict,war and conquest, andmetals have been a vitalpart of that development.

Metal has manyadvantages over stone,wood, or bone:

• metal is harder, stronger, and flexible, not brittle.

• metal can be cast, hammered or drawn into shapes notpossible in stone, such as saw blades, swords and armour.

• when tools become blunt, metal can be re-sharpened.

Basically, a warrior with a bronze sword always beats a blokewith a stone axe... we call that progress!

The Iron Age (approx. 2,500 to 1,500 years ago)About 1,000 B.C. the extraction of iron from its oreswas discovered. This requires much highertemperatures, and the breakthrough was probably theinvention of the bellows, a device to pump air into afurnace so the wood or charcoal burns hotter.

Iron is stronger and harder than bronze. A warriorarmed with iron weapons will usually beat a bronze-armed man. Iron tools and even the humble nailallowed new developments in buildings, ships,wagons... remember that towns, trade and commercegive wealth and power. An iron plough allows moreland to be cultivated to grow more food, to feed abigger army... and so on.

It is no accident that the dominant world power of thistime was ancient Rome, because their technologywas based on iron.

From the Medieval to the ModernAfter the collapse of the Roman Empire the variouscultures that dominated the “Dark Ages” still had iron-based technologies.

The next great technological change was the“Industrial Revolution” which began about 1750 inEngland. This had many aspects, but the big changein technology was the use of coal (instead of wood) forfuel. As well as steam engines, coal allowed for largescale smelting of iron and the invention of steel (analloy of iron with carbon).

The engines, tools and machinery of the greatfactories were based on steel. Transport wasrevolutionised by steel locomotives running on steelrails. Steel ships replaced wooden ones, and steelweapons (machine guns, tanks and artillery) achievednew heights (depths?) in warfare and mass destruction.

In the 20th century, new metals and alloys became available... aluminium, titanium,chromium, and many more.

This was made possible by electricity, which isneeded in large amounts to extract some metals fromtheir ores, or to purify and process them onceextracted.

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The Metals We Use TodayIn one sense, we are still in the “Iron Age”. Ironis still the metal we use the most, but nearlyalways it is mixed with other elements in avariety of alloys, notably steel.

Steel is used for bridges, tools and machinery,bolts, screws and nails, reinforcing insideconcrete structures, engines, vehicle bodies,trains and their rails, ships, and “tin” cans.

Why is steel so widely used?• Iron ore occurs in huge deposits, so iron is

common and economical to produce.• Steel (in its various forms) is hard and strong.• It can be cast, milled, rolled, worked, bent, cut

and machined into any shape or size.

As always, our usage of the different steel alloysis linked to their particular properties:

Steel Iron, Properties UsesAlloy with...

Mild steel 0.2% strong, but car bodies,carbon malleable pipes, roofing

Tool steel 1-1.5% very hard drills, knives,carbon hammers

Stainless 20% nickel resists food utensils,Steel & chromium corrosion, medical tools

hygenic

Brassis a common “non-ferrous” (no iron) alloy.

Brass is an alloyof copper andzinc (about 50%each)

Brass is very hard, but easily machined for screwthreads, etc. It is more expensive than steel, but iscorrosion resistant, so it is ideal for taps andfittings for water and gas pipes.

Solder is an alloy of 30-50% tin with lead.

Its most notable property is a very low meltingpoint, around 150-200oC.

Its major use is in plumbing for sealing the jointsbetween pipes, and in electronics for connectingsmall components on a “circuit board”.

Metals That Are Used in Their Pure State

Although we use a wide range of alloys, there aresome important metals we use in their pure,elemental state.

Aluminium is very lightweight, yet strong andcorrosion resistant

Its lightweight strength isperfect for aircraftconstruction.

Lightweight and a goodconductor, it is used forelectricity power lines.

Malleable and corrosion resistant, it is ideal forwindow frames and drink cans.

Copper is used for electrical wiring in buildings andappliances, because of its great electrical conductivityand its ductility for ease of wire-making.

Metal Extraction Needs EnergyOur use of different metals through history can belinked to the availability of energy.

In topic 1, you learned about the process ofchemical decomposition; where a compoundbreaks down into simpler substances.

Decomposition is generally an endothermicprocess; energy is absorbed by the reactantsduring the reaction. Generally, you must supplyenergy to make the process happen.

Metal ores are mineral compounds. To obtain theelemental metal involves decomposition, which isendothermic and requires energy. Somecompounds require more energy than others fordecomposition.

Copper and tin ores require little energy. A decentwood fire can “smelt” the metal from its ore. This whycopper and bronze were used in ancient times.

Iron ore requires more energy for decomposition.That’s why the “Iron Age” came later.

Aluminium and other “modern” metals requireeven more energy, and electricity works betterthan heat, so these only became available in quiterecent times.




Before metals, people used tools mainlymade from a)............................. or................................. The first metal usedwas probably b).................................,because it occurs in the elemental statein nature. However, it is too soft to beused for tools, so was just used forc)................................

Metallurgy (the technology of metals)began with the extraction ofd).............................. from ores that weresimply e).........................................................................................A big improvement was the mixing ofores of f)....................... and ......................This produced the alloy g).......................,which made tools and weapons withmany advantages over stone:

• metal is h).................... and ....................and is not i)........................ like stone.

• metal can made into intricate shapes,such as j)..........................., not possiblein stone.

Later, bronze was replaced byk)...................... which is l)...................................... and....................., butrequires more m)............................ for itsextraction.

During the “Industrial Revolution”, theuse of n)................. for energy led to theproduction of o)............................ whichis iron with a small amount ofp)........................... in it. This allowed thedevelopment of machinery, trains andthe modern industrial world.

In the 20th century new metals such asq).............................. became availablebecause the r)..................................needed to extract it from itss)................... was available.

Today, the metal we use most is stillt)...................., in the form of the alloyu)................... Its widespread use isbecause:• it is common and v)................................to produce.• it is very w).................. and .....................Steel comes in a variety of alloys,including x).................. steel (car bodies,pipes, roofing) and y)....................... steelused for food utensils and medicaltools.

Other alloys used widely include: • brass, a mixture of z).................... and........................• aa)................................., with a very lowmelting point, is an alloy ofab)........................ and ..............................and is used in ac).....................................and ....................................

As well as many alloys, there are somemetals commonly used in their pure,elemental form:• Aluminium, which has the advantagesof being ad)......................... and resistantto ae)...........................Uses includeaf)..................................... and .............................................• ag)......................... is used for electricalwiring because of its goodah)............................... and because it isai)................................ so it is easy todraw out into wires.

Chemically, the extraction of metalsfrom ores involves aj)...............................reactions, which are ak).............-thermic.Some metals, such asal)............................. require very littleenergy, others such asam)...................................... require muchmore. In many cases an)...........................works better than heat in the extractionand purification processes. Thechanges in ao)............................ usagethrough history can be directly linked tosociety’s changing sources and uses ofap)......................................

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Practice Test Questions are at the endof the next section

Worksheet 1 Our Use of MetalsFill in the blank spaces. Student Name...........................................

Metals React With OxygenOne of the most familiar laboratory reactions isthe burning of magnesium:

In fact, many metals will burn, some a lot morereadily and violently than magnesium:

In these cases there is a violent exothermicreaction, with light and heat energy produced.The product is often a powdery, crumbly solid.

Other metals, such as aluminium and zinc, reacton the surface and the oxide compound formedis airtight and prevents further reaction. That’swhy these metals are often dull-looking... thesurface coat of oxide is dull.

Other metals, such as copper, react with oxygenvery slowly and only if heated strongly. Some,like gold, will not react at all.

The point is, that different metalshave different chemical activities.

Metals React With WaterAnother favourite school reaction is when sodiumreacts with water. This is often done outdoors,because it results in an exciting little explosion.

What happens is:

(In fact this is NOT the explosion reaction. Theexplosion is the reaction of the hydrogen withoxygen, to form water)

Once again, some metals react easily andrapidly and form the metal hydroxide, whileothers react slowly if heated in steam, and formoxides.

Metals like copper and gold do not react at all.

There is an “Activity Series” of metals.

Metals React With AcidsThe different activity levels of the metals is mostclearly seen when metals are reacted with dilute acids.

You may have done experimental work toobserve how vigorously different metals reactwith a dilute acid.

Metals like calcium andmagnesium reactvigorously.

Zinc and iron are slower.

Lead is very slow indeed.

Copper does not react atall.

When there is a reaction,the gas produced ishydrogen.

The metal is “eaten away”and dissolves into the liquid.This is because it forms asoluble ionic compound. Exactly what thecompound is, depends on which acid is used.

The ionic compounds formed are collectivelyknown as “salts”, so the general pattern of thereactions is

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2. CHEMICAL ACTIVITY OF THE METALSkeep it simple science

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It will help you greatly to learnthe common laboratory acids

Common Name Chem Name FormulaHydrochloric = Hydrogen chloride HClSulfuric = Hydrogen sulfate H2SO4Nitric = Hydrogen nitrate HNO3

Bubbles ofgas are

produced.

A flame testgives a “pop”

explosion

Metal + Acid Hydrogen + a Salt

WORKSHEET at end of section

Magnesium + Oxygen Magnesium oxide2 Mg + O2 2 MgO

Examples:

Zinc + Hydrochloric Hydrogen + Zincacid chloride

Zn + 2 HCl H2 + ZnCl2

Magnesium + Nitric Hydrogen + Magnesiumacid nitrate

Mg + 2 HNO3 H2 + Mg(NO3)2

Iron + Sulfuric Hydrogen + Iron(II)acid sulfate

Fe + H2SO4 H2 + FeSO4

Sodium + Oxygen Sodium oxide4 Na + O2 2 Na2O

Aluminium + Oxygen Aluminium oxide4 Al + 3 O2 2 Al2O3

Sodium + Water Hydrogen + Sodium(gas) hydroxide

2 Na + 2 H2O H2 + 2 NaOH

Zinc + Water Hydrogen + Zinc oxideZn + H2O H2 + ZnO

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The Activity Series of the MetalsFrom these 3 patterns of reaction, it seems thereis a further, underlying pattern. Certain metals,like sodium, always seem to react readily andvigorously. Others, like copper, always reactslowly or not at all.

From this, and other reaction studies, thecommon laboratory metals can be arranged inan “Activity Series”:

Electron Transfer in Metal Reactions

The chemical reactions that allow us to see thepattern of the Activity Series are just part of aneven greater pattern in Chemistry... the processof electron transfer.

To understand this, look again at the reactionbetween a metal and an acid:

HCl and ZnCl2 are both ionic compounds. Hereis the equation re-written to show the individualion “species”.

Study this carefully and make sure youunderstand why there have to be 2 of some ionsto agree with the original balanced equation.

Notice that the chloride ions (Cl-) occur on bothsides of the equation unchanged. Nothing hashappened to them at all. We say they are“spectator ions”. Like by-standers at a car crashthey are not involved, while other atoms andions undergo serious changes.

Since they aren’t actually involved, we can leavethe spectators out. This is called a “netequation”.

Now we can see what really happened; • a zinc atom became a zinc ion

and • 2 hydrogen ions became a (covalent)hydrogen molecule.

To do this, the zinc atom has to lose 2 electrons,and the hydrogen ions must gain a pair ofelectrons to share.

Now it should be clear what really happened: thezinc atom gave a pair of electrons to somehydrogen ions. Electrons were transferred fromone “species” to another.

The equations above are “Half-Equations” andare often used to describe what is reallyhappening in a reaction.




KNaLiBaCaMgAlZnFeSnPbCuAgAu

MostActive

LeastActive

If you look for these metals on the Periodic Tableyou will notice a further pattern.

Positions of the first 6 metalsof the ActivitySeries.

The highly active metals all lie to the extreme left ofthe table, AND the higher their activity, the lower downthe table they are within each column.

This is one of many patterns that allows you to usethe Periodic Table instead of learning many smallfacts. For example, instead of memorising the ActivitySeries fully, you can remember the pattern above andalways be able to figure out the order of the mostactive metals.

Zinc + Hydrochloric Hydrogen + Zincacid (gas) chloride

Zn + 2 HCl H2 + ZnCl2

Zn + 2H+ + 2Cl- H2 + Zn2+ + 2Cl-

Zn + 2H+ H2 + Zn2+

Zn Zn2+ + 2e-

2H+ + 2e- H2

123

4

56

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Oxidation and ReductionThe transfer of electrons from one species toanother is one of the most fundamental andimportant general reactions of Chemistry.

The reaction between zinc and acid can bevisualised like this:

The zinc atom has lost 2 electrons,

and the hydrogen ions have gained electrons.

Neither process can occur alone... they mustoccur together

The zinc oxidation allows the hydrogen to bereduced, and the hydrogen reduction allows thezinc to be oxidised.

The total reaction is an “Oxidation-Reduction”and is commonly abbreviated to “REDOX”.

Note that the syllabus does NOT require you toknow these definitions yet, but it is worthknowing about Redox for future topics. You ARErequired to know about electron transfer and itsinvolvement in metal reactions.

First Ionisation EnergyAlthough you’re not yet required to knowabout Oxidation and Reduction, this bit youhave to learn.

DefinitionThe Ionisation Energy of an element is theenergy required to remove an electron froman atom.

For technical reasons, the measurement of thisenergy is carried out for atoms in the gas state.

We know that zinc atoms normally lose 2electrons to form the Zn2+ ion. However, theformal definition for this process involvesjust the loss of 1 electron.

Every element has its own characteristicvalue, even those elements which would notnormally lose electrons, such as non-metalslike chlorine.

Even the inert gases, which normally do notform ions at all, can be forced to lose anelectron if energy is added. They too have a1st Ionisation Energy value.

Ionisation Energy Determines the Activity SeriesIn order for a metal to begin reacting with anacid, (or with water or oxygen) it must lose anelectron. This will require the input of its 1stIonisation Energy.

If the value for 1st Ionisation energy is verylow, the metal will gain this energy easily andquickly from its surroundings. It will readilyenter the reaction, and the reaction willproceed vigorously.

If its value for 1st Ionisation energy is higher,the atom cannot react so readily orvigorously... its activity is lower.




+

+2

+

Zinc atom

Zinc ion

electrons transferred

2 Hydrogen ions

Hydrogen molecule

Covalent bond(2 electrons being shared)

Zn Zn2+ + 2e-

For historical reasons, the loss of electrons is called “Oxidation”

Cl(g) Cl+(g) + e-

Normally a chlorine atom forms a negative ionby gaining an electron.

Technically though, it is possible for it to losean electron if energy is added.

This energy is the “1st Ionisation Energy”

Zn(g) Zn+(g) + e-

The energy required for this to happen is the“1st Ionisation Energy”

2H+ + 2e- H2

The gain of electrons is called “Reduction”

WORKSHEET at the end of section The ACTIVITY SERIES of the Metalsis determined by

1st IONIsATION ENERGY

KNaLiBaCaMgAlZnFeSnPbCuAgAu

Incr

easi

ng v

alue

s fo

r 1s

t Io

nisa

tion

Ener

gy

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Choice of Metals Based on Activity

Sometimes which metal is chosen for aparticular application is based on its position inthe Activity Series.

ExampleIn critical electronic connections, such ascomputer network plugs, it is essential that theelectric signals get through without loss ordistortion.

Normally we use copper for electrical wiring, butin a critical connection plug it is worth the extraexpense of using gold.

Copper is a low activity metal, but can slowlyreact with oxygen to form a non-conductingoxide layer in the connection. Gold is lowerdown the activity series and will not react at all,so the plug connection cannot corrode.

Gold’s extremely low chemical activity (due toa relatively high 1stIonisation Energy)is part of thereason it hasalways been usedfor jewellery.

Gold’s low activitymeans it will nottarnish or corrode,so it retains itsbeautiful colour andlustre.

Another example is the choice of metals forwater pipes.

Steel is cheap, butsince iron is about themiddle of the ActivitySeries it will corrode(rust) by contact withwater. Is it better tochoose a lower activitymetal such as copper,which will not corrodeas quickly, but is moreexpensive?

The decision is usuallyto use cheap steelpipes for longer,outdoor uses like yourgarden taps.

Indoors, wheredistances are shorter,copper is chosen,especially for hot watersupply. Indoors arusted-out leaking steel pipe would be adisaster, so it’s worth paying more for copper.

Interestingly, sometimes the higher activitymetals corrode less. Aluminium and zinc arehigher up the Activity Series than iron. Theyreact rapidly when exposed to oxygen, but thesurface layer of oxide is airtight and waterproof,and prevents oxygen or water getting to themetal underneath. Therefore, these metals canbe used in situations where corrosion needs tobe prevented.

“Galvanised” steel is coated with a thin layer ofzinc to prevent (or slow down) corrosion of steelroofing, fence wires, nails, bolts, etc.




Brass fittings

Copper pipe

Bronze & Gold have been used throughout history

in Art and Religion


When a metal reacts with oxygen it forms ana)......................... compound.

Some metals will also react with water, formingc)..................................... gas and ad)...................................... compound.

Most metals will react with acids, forminge).......................... gas and an ionic compoundcalled a “f)...........................”

In all these reactions the various metals react atg)............................... rates, showing an order ofchemical h)......................... From these reactionsand others, the “Activity Series” has beendetermined.

Metals such as i).............................. and............................. are the most active. These arethe elements located in the j)...........................columns of the Periodic Table.

Some metals such as k)....................... and......................... have very low activity, and oftendo not react at all. Other common metals likel).................................. and ....................................are in the middle of the series. They will react,but generally do so m).......................................

4. All the following equations are Metal + Acidreactions.Fill in all blank spaces, then re-write in symbols andbalance.

a) Zinc + Sulfuric acid ................. +.....................

b) Calcium + Hydrochloric ................. +...................acid

c).................. +...................... Hydrogen + Bariumnitrate

d).................... + .................... Hydrogen + iron(II)chloride

5. For each of the reactions in Q4, which chemicalspeciesa) lost electrons?

b) gained electrons?

c) was a “spectator”?

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METAL + OXYGEN b) .............................

METAL + WATER c).................. + d).................

METAL + ACID e)....................... + f).................

Worksheet 2 Chemical Activity of the MetalsFill in the blank spaces. Student Name...........................................

Worksheet 3 Practice Problems Student Name...........................................

All these reactions involve the transfer ofn)......................... In the case of the Metal + Acidreaction, the metal atoms alwayso)......................... electron(s) while a pair ofp)............................ ions gain 2 electrons (whichthey share in a q)......................... bond) and forma r)...................... molecule with formula s)...........

“Oxidation” is the technical term fort)..................... ................................. The oppositeis “u)...................................”In the Metal + Acid reaction, the metal is alwaysv).............................................. whilew).............................. ions are alwaysx)..................................................

The “1st y)........................... Energy” of anelement is defined as the energy required toz)......................................... ................... fromatoms in the aa)................. state. The very activemetals are like that because they have veryab).................... (high/low) values for this. Metalsfurther down the series do not react asvigorously because their values areac)...........................................

Sometimes the choice of which metal to use isdetermined by the activity level. An example isad)............................... .... ....................................................................................

1. Write a balanced, symbol equation for the reactionof each of the following metals with oxygen.

a) Lead (assume lead(IV) ion forms)

b) Iron (Assume iron(III) ion)

c) Lithium

2. a) Arrange the metals in Q1 in order of decreasingchemical activity.

b) Which one(s), if any, might ignite easily and burnin air with a visible flame?

3. Write a word equation AND a balanced, symbolequation to describe the reaction of:a) calcium metal with water (reacts spontaneously atroom temperature)

b) Tin metal with water (heated in steam) (Assumetin(II))

Multiple Choice1.Which list shows metals used by humans in thecorrect chronological order of their history of usage?A. bronze, aluminium, ironB. copper, bronze, ironC. gold, iron, bronzeD. copper, steel, bronze

2.Which list correctly identifies an alloy, and theelements it contains?A. Steel; iron and tinB. Bronze; tin and zincC. Solder; copper and leadD. Brass; copper and zinc

3.The metals used by humans have changed over thecourse of history. The availability of new metals hasoften been dependent on the:A. availablity of energy to extract metals from ores.B. discovery of new minerals as people explored

the world.C. invention of new alloys.D. development of new technologies to use

the metals.

4.A metal which reacts readily and vigorously withoxygen, water and dilute acids would probably:A. have a high value for 1st ionisation energy.B. be from the “Transition” block of the

Periodic Table.C. have a very low 1st ionisation energy.D. be located at extreme right of the Periodic Table.

5.If nickel reacted with sulfuric acid, the products of thereaction would be:A. hydrogen gas and nickel sulfateB. carbon dioxide gas and nickel sulfate.C. nickel sulfide and hydrogen gas.D. sulfur dioxide gas and nickel hydroxide.

6.During the reaction in Q5, the basic underlyingchange occurring is:A. the breaking covalent bonds.B. the transfer of electron(s) from one species

to another.C. chemical changes in “spectator ions”.D. physical dissolving of metal in the acid.

Longer Response QuestionsMark values shown are suggestions only, and are togive you an idea of how detailed an answer isappropriate. Answer on reverse if insufficient space.

7. (5 marks)Give an example of

a) a metal used in its elemental state, and

b) a non-ferrous alloy (naming its components)in common use. For each, relate the properties of themetal to its particular use(s).

8. (3 marks)Give a reason whya) metal tools are superior to stone tools.

b) iron replaced bronze in the history of metallurgy.

c) aluminium did not come into common use until the20th century.

9. (6 marks)The most common metal in use today is steel, whichcomes in a variety of forms, with different propertiesand uses. Compare 3 different types of steel, statingthe composition of each and relating its properties toa common use.

10. (5 marks)Give an outline of an experiment you have done toinvestigate the relative chemical activity of somemetals. Include the observation(s) you made toassess metal activity, and state the conclusion(s)reached.

11. (6 marks)Write a balanced symbol equation for the reaction of:a) magnesium with hydrochloric acid.

b) calcium with water (reacts at room temperature).

c) potassium with oxygen.

12. (4 marks)When barium metal reacts with an acid there is anexchange of electrons such that hydrogen gas andbarium ions are formed. Write 2 “half-equations” toshow clearly the species gaining, and the specieslosing, electrons.

13. (4 marks)a) Write an equation (including states) for the firstionisation of i) magnesium

ii) oxygen

b) Describe how the Activity Series of Metals isrelated to the values of 1st Ionisation Energy.

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Worksheet 4 Test Qestions sections 1 & 2 Student Name...........................................


Electrons = Protons = “Atomic Number”

Each element’s atoms have a different,characteristic, number of protons (andelectrons). Therefore, each element has adifferent Atomic Number.

In the Periodic Table the elements are arrangedin order of Atomic Number.

Protons + Neutrons = “Mass Number”(Electron mass is insignificant)

The Mass Number is always a whole number,but in the Periodic Table the “Atomic Weight” isshown instead.

(How and why this is different will be explained in a later topic)

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3. PATTERNS OF THE PERIODIC TABLEkeep it simple science

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In orbit aroundthe nucleus arethe Electrons

In the NucleusareProtons & Neutrons

Atomic Structure, Atomic Number and MassHere is a quick reminder of some basics about atoms you need to know:

The Periodic Tableis firstly a list of the elements, arranged in order,and showing all the basic details.

However, the Periodic Table is far more than asimple list. Why is it such a complicated shape?

The shape and arrangement of the PeriodicTable is a very clever device to allow manypatterns and groupings to be accommodated.You have already learnt one pattern in theposition of the most active metals, and their 1stIonisation Energies.

There are lots more...

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ArArgon39.95

Atomic NumberEqual to the number of protonsin each atom. (Also equals thenumber of electrons in theneutral atom.)

Chemical Symbol

Element Name

“Atomic Weight”NOT the “Mass Number”

History of the Periodic TableThe modern concept of a chemical elementdeveloped almost exactly 200 years ago.

By 1830 there were about 40 known elements.Even with such a small sample, people began tonotice patterns:

Dobereiner (German) pointed out that therewere several groups of 3 elements withremarkably similar properties:

Lithium, sodium & potassium was one “triad”.Chlorine, bromine and iodine formed another “triad”.

By 1860, with over 60 known elements,Newlands (English) proposed a “Law ofOctaves”.

If the elements were arranged in order of relativeweights, Newlands found that every 8th element(an “octave”) was similar in properties. Thesesimilar elements included Dobereiner’s triads.

The system worked well for the first 20 elements,but then became confused.

The basis of the modern Periodic Table wasdeveloped by the Russian, Dmitri Mendeleevin 1869.

Mendeleev used many physical and chemicalproperties:• atomic weight • density• melting point • formula of oxide compound• density of oxide and many more,

and arranged the elements in order of weight, butwith elements with similar properties under eachother.

Mendeleev’s genius was to realise that there wereprobably missing elements that hadn’t beendiscovered yet. He cleverly left gaps in his table forthese undiscovered elements.

The most famous case was that of the “missing”element Mendeleev called “eka-silicon”. He used thepatterns in his table to predict, very precisely, theproperties for eka-silicon. Scientists went looking forsuch a substance and soon found a new element(which was named “Germanium”) with propertiesexactly as predicted.

Similar elements placed invertical columns Inert Gases had NOT

been discovered

Mendeleev’s vertical “families”included Dobereiner’s “triads”and Newland’s “octaves”, but

had one big difference...




13

Patterns of the Periodic TableIn Mendeleev’s day no-one could explain why these patterns existed.

However, when scientists see patterns in nature like this, they know there must beunderlying “rules” or “laws of nature” causing and controlling the patterns.

Perhaps Mendeleev’s great contribution was not just the Periodic Table itself, but the stimulus it gave other scientists to investigate the reasons behind the patterns.

Within 40 years Science had unravelled the secrets of atomic structure, the electron energy levels, and more.

At this stage, your task is to learn some of the patterns.

Electrical ConductivityAs you go across any row (“period”) of the table,you will move through a number of metals, then oneor two semi-metals, then into the non-metals.

Therefore, the conductivity will start out high, butrapidly decrease as you encounter a semi-metal,and become extremely low at the non-metals.

Conductivitydecreasing

Semi-Metals

Melting PointYou learned in topic 1 how melting point is determined bythe bonding within a substance.

At the left side of the table are the very active metals of theActivity Series. They are also usually soft, and haverelatively low (for metals) melting points.

Moving to the right across a period you enter the “TransitionBlock” containing typical hard, high melting point metals,held strongly together by “metallic bonding”.

Further right you hit the Semi-Metals. These often have veryhigh melting points because of their covalent latticestructure.

Then you enter the Non-Metals which have covalentmolecular structures and quite low mp’s. At the far rightcolumn, each period ends with an Inert Gas which are allsingle-atom molecules, and have the lowest mp of eachperiod.

This pattern repeats itself along each period.

Mel

ting

Poin

t (o C)

01,

000

2,

000

Atomic Number

Sketch Graph. Melting Points of Elements

Periods 3

Period 4

Na

Si

K

Ar

V

Kr

Rb

Inert Gases

Boiling Points follow a similar pattern to

Melting Points

Chemical Bonding, Valency & ReactivityWhat you’ve already learnt about the Activity Series, Ionic and Covalent Bonding and Valency

will help you make sense of the following:

+1

+2 -11-33+3 4 -22

0

Valencies are the samedown each group

Group 8 Inert GasesNo chemical reactions,

no bonding

Activity of Metals

Most active at bottom-lleft.

Activity (generally)decreases upwardsand to the right.

Activity of Non-MMetals

Most active at top-rright(Fluorine)

Activity (generally)decreases downwards

and to the left.

Peaks are Transition Metalsor Semi-MMetals

MetalsNon-

Metals

Non-MMetals(Covalent or (-vve) ions)

Semi-MMetals(Covalent only)

Bonding

Metals(+ve ions)




14

Atomic RadiusThe size of an atom is the distance across its outer electron shell.

You might think that the atoms along each period would be thesame size, because it’s the same orbit being added to.

However, the increasing amount of positive charge in thenucleus pulls that orbit inwards closer and closer to the centre.

The following diagramsare to scale and show

the relative sizes of thefirst 20 elements

H37

He50

Li152

Be112

B88

C77

N70

O66

F68

Ne70

Mg160

Al143

Si118

P110

S102

Cl99

Ar94

Radius decreasing across a period

Radi

us in

crea

sing

dow

n a

grou

p

Down each group the radius increases.This is because, as you go down a group, you have addedan entire electron shell to the outside of the previous layer.

The numbers given are the atomic radii in picometres.1 picometre = 1x10-112 metre

Na186

K231

Ca197

The Syllabus requires that youproduce a table and a graph ofthe changes in a property

• across a period,and • down a group

When you do, you can clearlysee how the Periodic Table gotits name.

“Periodic” means “recurring atregular intervals”.

This graph shows what aspreadsheet plot gives for theradii of the first 37 elements.

Notice how the same graphicalpattern keeps recurring... it is aperiodic pattern.

There are a number of irregularities and “glitches”apparent on the graph. It is beyond the scope of

this course (and way beyond the K.I.S.S. Principle)to attempt an explanation of these.

RbK

NaLi

He NeAr

Kr

Decreasing Trend

across a period

Increasing Trend

down a group

Increasing Trend

down a group

1 10 20 30

Atomic Number

Spreadsheet Plot of Atomic Radii

Atom

ic R

adiu

s (p

icom

etre

)0

10

0

20

0

30

0




15

Ionisation EnergyThe meaning of the “1st Ionisation Energy” wasexplained previously in relation to the ActivitySeries of Metals.

Any atom can lose an electron if enough energyis supplied... even atoms which do not normallylose electrons.

The Periodic Trend in 1st Ionisation Energy

You should remember that the very activemetals are the ones with low 1st ionisationenergies. They easily lose their outer electron(s)and so react readily.

The trend for the whole Periodic table is:

Explanations:1st I.E. increases to the right because each atomacross a period has more and more (+ve)nuclear charge attracting and holding electronsin the orbit concerned. Therefore, it requiresmore energy to remove an electron.

1st I.E. decreases down each group because, ateach step down, an extra whole layer of electronshas been added to the outside of the atom. Theouter shell is further away from the nucleus, andis partially “shielded” from nuclear attraction bythe layers of electrons underneath it. Therefore, itbecomes easier and easier to remove an electron.

Successive Ionisation EnergiesHaving added the energy of 1st I.E. and removedan electron from any atom, it is then possible toadd more energy and remove a 2nd electron,and a 3rd, and so on.

Once the first electron is removed, theremaining electrons are pulled in tighter to thenucleus. Each one experiences increased forceof attraction, so it requires more energy toremove the next electron. Therefore, eachsuccessive ionisation requires more energy.

Once the entire outer orbit has been strippedaway, the next ionisation must remove anelectron from an underlying orbit, whichrequires a huge increase in the next ionisationenergy. This results in an interesting pattern:

Notice how the values “jump” (underlined data)as the next ionisation has to remove an electronfrom the next lower orbit.

A(g) A+(g) + e-

where “A” stands for any atomin the gas state

1st I.E. A(g) A+(g) + e-

2nd I.E. A+(g) A2+

(g) + e-

3rd I.E. A+2(g) A3+

(g) + e-

...and so on,according to how many electrons

the atom has

Highest value

Lowest increasing

decr

easi

ng

1st IonisationEnergy

Patterns in Successive Ionisation Energy Data(values shown are energy units)

Successive Elements on Period 3

Element Electron 1st 2nd 3rd 4thConfig. I.E. I.E. I.E. I.E.

Sodium 2.8.1 0.5 4.5 6.9 9.6

Magnesium 2.8.2 0.7 1.4 7.7 10.5

Aluminium 2.8.3 0.6 1.8 2.8 11.6

Highest Value Inert gasesFluorine not included

Electronegativityis a value assigned to each element to

describe the power of an atom toattract electrons to itself.

Atoms with a tendency to gainelectrons and form negative ions have

high values.Atoms with a tendency to lose

electrons easily (low 1st I.E.) and form(+ve) ions have very low values.

Once again, there is a pattern in thesevalues in the Periodic Table.

2.2

2.5

2.8

3.0

4.03.53.02.52.0Electronegativity Values

of selected elements(values decrease to left)

1.51.0

0.9

0.8

0.8

0.7

0.7

(val

ues

decr

ease

dow

n)




As early as 1830, the Germana)....................................... noticedpatterns in the properties of theelements. In 1860, the English scientistb)................................ proposed a “Lawof c)..............................” describing therepeating pattern of properties.

It was the Russian d).................................who invented the e)............................................, in more or less its modernform. He realised that there wereprobably many elements that had notf)........................, so he g).............................. in his table for lateradditions. By studying the details ofknown elements, he was able toh)........................ very precisely theproperties of the missing elements.

Sure enough when discovered, themissing elements were found to haveproperties i)............................................

The patterns in the Periodic Tableinclude:

Conductivity, which generallyj)............................ to the right, as you gofrom metals to k).................................and ...............................

Melting Points: tend to l)........................to about the middle of each period, thenm)............................. The highest value isusually a n)..................... metal or one ofthe o)............................... elements. Thelowest value on each period is alwaysthe p)............................. gas member onthe extreme q)......................... (right/left)

Valencies are r)............................... downeach vertical group. Bonding followsthe pattern of the main categories ofelements. s)........................... formt)........................... bonds when they loseelectrons and become u)....................ions. The Semi-metal elements formonly v)........................... bonds. The Non-metals can bond w)................................or can x).................. electrons to formy)................. ions.

Chemical Reactivity is different formetals and non-metals. The most activemetals are located at the leftz)......................... (top/bottom) of thetable. Generally, activity decreasesaa)...................... and to theab)............................. The Inert Gasesshow no chemical activity. Apart fromthem, the most active non-metals arelocated on the right ac)............................(top/bottom) of the table. Activitygenerally decreases as you movead).......................... and ...........................

Atomic Radius ae) ....................................across a period because eachsuccessive element has af)......................(more/less) positive charge in theag)........................ to attract the electronshell and pull it inwards. As you godown a group the radiusah)........................... as each newelectron shell is added.

First ai)........................ Energiesaj)....................... across a period, as theincreasing amount of nuclear chargemakes it more and more difficult toak)............................ an electron. Thevalues al)...................... down a groupbecause each extra shell of electrons isam)................. (more/less) strongly heldthan the previous.

Successive Ionisation Energiesmeasure the energy required toan)............................ another,subsequent electron from an atom. Theenergy required to remove the nextelectron is always ao)...............................(higher/lower). When the next electronhappens to be in the next lower shell,the value ap)................................ by ahuge amount.

aq).................................... is a valuewhich describes the power of an atom toar)............................. electrons. Theelement with the highest value isas)............................, and valuesdecrease as you move to theat)......................... and as you moveau)............................ the Periodic Table.

16

Worksheet 5 Patterns of the Periodic TableFill in the blank spaces. Student Name...........................................

WHEN COMPLETED, WORKSHEETSBECOME SECTION SUMMARIES

Multiple Choice1.The scientist most responsible for thedevelopment of the Periodic Table was:A. Avogadro B. NewlandsC. Gay-Lussac D. Mendeleev

2.Element “X” is in Group 2 and element “Y” in Group 7.

If X & Yformed a compound,you would expect it to be

A. ionic, with formula X2YB. covalent, with formula X2YC. ionic, with formula XY2D. covalent, with formula Y2X

3.If the elements “X” & “Y” in Q2 lie in the sameperiod of the table, you would expect:A. X to have a smaller radius than Y.B. Y to have a higher electronegativity than X.C. X to have a higher 1st ionisation energy than Y.D. Y to have a higher melting point than X.

4.The reason for the trend in atomic radius as youmove across a period to the right, is:A. increasing nuclear charge.B. addition of extra electron shells.C. decreasing attraction of electrons to the nucleus.D. increasing mass of the atoms.


5. (5 marks)a) Write equations to represent the 1st, 2nd, 3rd& 4th ionisations for a calcium atom.

b) Between which two of these successiveionisations would you expect a huge increase inthe required energy?

6. (5 marks)a) Sketch a graph (values are not required) toshow the general changes in melting points ofthe elements across one period of the PeriodicTable.

b) Briefly explain the general trend shown inyour graph.

7.On each of the following Periodic Tablediagrams label the arrows with the word“increasing” or “decreasing” to correctlydescribe the trend in the direction shown.

a) Atomic Radius

17




Worksheet 6 Patterns of the Periodic Table Test Questions Student Name...........................................

b) Electronegativity

Also indicate (“H”&“L”) the position of elements with highest & lowest values.

c) 1stIonisationEnergy

Show“H”&”L”

i)

ii)

i)

ii)

i)

ii)

Quantities in Chemical Calculations

Atoms, molecules and ions always react with eachother in fixed, whole-number ratios. That’s whybalancing an equation is so important... it actuallybrings the equation into line with what is happeningat the particle level.

For example, when hydrogen and oxygen react toform water, the balanced equation is

2H2 + O2 2H2O

This is a true description of what is happening to themolecules:

However, when we carry out chemical reactions in thelaboratory or in Chemical Industry, we cannot see orcount the molecules. Instead, we measure the massor volume of substances.

To measure out the correct numbers of particles for areaction we need a simple way to convert masses andvolumes to numbers of molecules, and vice-versa.That’s the purpose of

The Mole1 mole is a quantity of a chemical substance.

1 mole of any element or compound containsexactly the same number of particles.

1 mole of each substance has a different mass,because the atoms and molecules all weighdifferently.

The really clever and convenient thing about themole is its link to the Periodic Table and the“Atomic Weights” shown.

1 mole 1 mole 1 mole= 12.01 grams = 39.95 grams = 207.2 grams

Defining the MoleFor technical reasons, the “atomic standard”used to compare the masses of all atoms is thecarbon atom, which contains

6 protons6 neutrons6 electrons

Atomic Number = 6Mass Number = 12

The mass of this atom isdefined to be exactly 12.000000atomic mass units (a.m.u.) and all other atomsare given masses relative to this one.

Since this is the standard of comparison, theformal definition of the mole is:

“the number of atoms contained in exactly 12 grams of carbon-12”

Avogadro’s NumberJust how many atoms are in 1 mole?

Obviously, it is a very large number. We nowknow that it is about 6,000 billion trillion.

This number is named in honour of an Italianscientist who you will learn about soon.

18

4. QUANTITY CALCULATIONS & THE MOLEkeep it simple science

®



1 Molecule of O2

2 Molecules of H2

2 Molecules of H2O+

6C

Carbon12.01

18ArArgon39.95

82PbLead

207.2

6p+

6n0

Note: In Topic 1 it was pointed out that the MassNumber for any atom is a whole number. It has stillnot been explained why the “Atomic Weights” in the

Periodic Table are mostly not whole numbers.

This WILL be explained in a later topic. If you cannot wait, go find out about “Isotopes”.

Avogadro’s Number6.022 x 1023

particles in 1 mole of anything

207.2 grams ofLead

contains6.022 x 1023

Lead atoms

39.95 grams ofArgon

contains6.022 x 1023

Argon atoms

12.01 gramsof

Carboncontains

6.022 x 1023

Carbon atomsEACH OF THESE HAS THE SAME NUMBER OF ATOMS

19

Calculating Mole QuantitiesYou need to be able to calculate mole quantitiesin terms of both mass and number of particles.

Molar MassThe “Molar Mass” of any chemical species is themass (in grams) of 1 mole of the substance.

You need to add up all the Atomic Weights of allthe atoms given in the formula.

Examples:Name Formula Molar Mass (g)Argon Ar 39.95 Sodium Na 22.99

(for elements like these just use Atomic Weight)

Oxygen O2 (16.00 x 2) = 32.00Chlorine Cl2 (35.45 x 2) = 70.90

(these elements are diatomic molecules... 2 atoms each)

Water H2O (1.008x2 + 16.00) = 18.016Carbon Dioxide CO2 (12.01 + (16.00x2)= 44.01Sodium chloride NaCl (22.99 + 35.45) = 58.44

(add up At.weights of all atoms in the formula)

Number of Moles in a Given MassWhen you weigh a chemical sample you thenneed to be able to calculate how many molesthis contains.

Moles and Numbers of ParticlesSince one mole of any substance containsAvogadro’s Number of particles:




No. of moles = mass of substance you havemolar mass

n = m MM

No. of moles = No. of particles you haveAvogadro’s Number

n = N NA

Worksheet at the end of this section


Example Calculations1. How many moles in a) 5.23g of magnesium?

b) 96.7g of water?

Solution a) n = m = 5.23 = 0.215 molMM 24.31

b) n = m = 96.7 MM (2x1.008 + 16.00)

= 96.7/18.016= 5.37 mol

2. What mass is needed if you want to have 1.50moles of salt (sodium chloride)?

n = m so m = n x MM = 1.50 x (22.99 + 35.45)MM = 1.50 x 58.44

= 87.7 g

Example Calculations1. How many moles are present in a sample of leadcontaining 7.88 x 1024 atoms?

Solution n = N = 7.88x1024

NA 6.022x1023

= 13.1 mol

2. a) How many atoms of lead are needed to make 0.0250 mole?

b) What would be the mass of this quantity?

Solutiona) n = N so N = n x NA = 0.0250 x 6.022x1023

NA = 1.51 x 1022 atoms

b) m = n x MM = 0.0250 x 207.2 (molar mass of Pb)= 5.18 g

Mole Quantities in Chemical Equations

When you consider an equation like

2H2 + O2 2H2Oyou know it means

However, the number of molecules reacting isreally just a ratio. The actual numbers might be

2 million H2 + 1 million O2 2 million H2O

or, 200 zillion H2 + 100 zillion O2 200 zillion H2O

or, (let’s use Avagadro’s number) (2 x NA) H2 + NA O2 (2 x NA) H2O

= 2 moles H2 + 1 mole O2 2 moles H2O

The Balancing Coefficients in a Chemical EquationMay be Interpreted as

Mole Ratios

1 Molecule of O2

2 Molecules of H2

2 Molecules of H2O+




20

Mole Quantities in Chemical Equations (cont.)

The balancing coefficients of an equation canbe interpreted as the mole ratio of reactants andproducts.

So, 2 H2 + O2 2 H2O

means 2 mol. reacts with 1 mol. to form 2 mol.or, 4 mol. reacts with 2 mol. to form 4 mol.or, 100 mol. reacts with 50 mol. to form 100 mol.or any other proportional quantities.

Calculating Mass Quantities in Reactions

Mole calculations allow you to calculate the mass ofproducts and reactants involved in a reaction.

Example Problema) If 0.50 mol of sodium reacted completely withhydrochloric acid, how many moles of productswould be formed?

b) What mass of each product would be formed?

Solutiona) The balanced equation is

2 Na + 2 HCl H2 + 2 NaClmoleratio 2 mol : 2 mol : 1 mol : 2 mol.

so, 0.50 mol : 0.50 mol : 0.25 mol : 0.50 mol

Answer: 0.25 mol of H2 and 0.5 mol of NaCl

b) Mass of Hydrogen: m = n x MM = 0.25 x 2.016= 0.50 g

Mass of salt: m = n x MM = 0.50 x 58.44= 29 g

Example ProblemAluminium burns to form aluminium oxide.If 4.29g of aluminium was burned, a) what mass of oxygen would be consumed?b) what mass of aluminium oxide would be formed?

SolutionAlways start with the balanced equation:

4 Al + 3 O2 2 Al2O3moleratio 4 : 3 : 2

No. of moles of Aluminium: n = m = 4.29 MM 26.98

= 0.159 mol

a) Mass O2 consumed:mole ratio Al : O2 = 4 : 3

∴ moles of O2 = 0.159 x 3 = 0.119 mol4

∴ mass of O2: m = n x MM = 0.119 x 32.00= 3.81 g

b) Mass Al2O3 produced:mole ratio Al : Al2O3 = 4: 2 (i.e. 2:1)

\ moles of Al2O3 = 1/2 x 0.159 = 0.0795 mol

∴ mass of Al2O3: m = n x MM = 0.0795 x 101.96= 8.11 g

Practical Work: Using Mass & Mole Ratios to Determine a Formula

A common experiment is to burn a piece of magnesium in a crucible, assuggested by the diagram.

Reaction: Magnesium + Oxygen Magnesium oxide

Careful measurement of mass allows the empirical formula for magnesiumoxide to be determined.

ceramiccrucible

Typical MeasurementsMass of empty crucible = 42.74 gMass of magnesium = 2.05 gMass of crucible + product after burning = 46.22 g

∴ Mass of magnesium oxide formed = 3.48 g

∴ Mass of oxygen incompound = 1.43 g

Analysis of ResultsRemember that to convert any mass to moles:

n = m / MM

Elements Magnesium : Oxygen Ratio of masses: 2.05 g : 1.43 g Ratio of moles: 2.05 / 24.31 : 1.43 / 16.00 (divide by Atomic Weight)

= 0.0843 mol : 0.0894 molSimplified ratio = 0.0843/0.00843 : 0.0894/0.0843 (divide both by the

= 1.0 : 1.06 smaller)Nearest whole number ratio 1 : 1∴ Empirical Formula is MgO There is often a large error

due to incomplete burning

Worksheet at the end of this section Worksheet at the end of this section


21

Gay-Lussac’s LawJoseph Gay-Lussac was a French scientist withan unfortunate name by modern standards. Helived 200 years ago, and was very interested inflight using balloons, so he investigated the waygases react chemically.

After a series of clever experiments, in which thevolumes of reacting gases were measured, in1808 he proposed the “Law of CombiningVolumes”:

The volume of a gas is easily changed by temperatureand pressure, so it is very important that the volumesare all measured at the same conditions.

Examples of Gay-Lussac’s Law

Hydrogen(g) + Chlorine(g) Hydrogen chloride(g)1 litre 1 litre 2 litres

Hydrogen(g) + Oxygen(g) Water(g) (vapour)2 litres 1 litre 2 litres

Hydrogen(g) + Nitrogen(g) Ammonia(g)3 litres 1 litre 2 litres

Notice that in every case, that the volumes arealways in a simple, whole number ratio to eachother.

Now consider the balanced equations for thesethree example reactions:

H2(g) + Cl2(g) 2 HCl(g)

2 H2(g) + O2(g) 2 H2O(g)

3 H2(g) + N2(g) 2 NH3(g)

The mole ratios are the same as the volumeratios discovered by Gay-Lussac!

Why should this be?

... enter Avogadro!



When measured at constant temperature and pressure, the volumes of gases in achemical reaction show simple, whole-

number ratios to each other.

A Little History... How the Mole was InventedAvogadro’s HypothesisThe Italian, Amadeo Avogadro (1776-1856) was trained inLaw, but became very interested in Science.

In 1811, he noticed the similarity between Gay-Lussac’s Law (an empirical “law” based onexperiment) and the concept that atoms mustcombine in simple, whole number ratios to formcompounds.

This led him to make an hypothesis:

This was a vital breakthrough in the history ofChemistry.

For example, consider the reaction:

Hydrogen(g) + Chlorine(g) Hydrogen chloride(g)

Prior to Avogadro, it was assumed that the thereaction involved single atoms, like this:

H(g) + Cl(g) HCl(g)

but the combining volumes (discovered byexperiment) were

Hydrogen(g) + Chlorine(g) Hydrogen chloride(g)1 volume : 1 volume : 2 volumes

Now, reasoned Avogadro, gases react in simple,whole-number volume ratios because each litreof gas has the same number of molecules in it.Therefore, to get the volume ratios shownabove, each hydrogen molecule, and eachchlorine molecule, must have 2 atoms!

i.e. Hydrogen is H2(g) and Chlorine is Cl2(g), andthe correct equation is

H2(g) + Cl2(g) 2 HCl(g)

Then, for the same reaction, scientists couldmeasure the masses of these gases as well asvolumes. This showed that chlorine atoms mustbe about 35 times heavier than hydrogen...chemists were on the way to figuring out therelative atomic weights of elements, and beingable to calculate chemical quantities.

Although he did not invent the concept of themole, we name the number of particles in 1 molein Avogadro’s honour... Avogadro’s Number.

Equal Volumes of all GasesContain Equal Numbers of Molecules

(when measured at the same conditions of temperature and pressure)


22

Molar Volume of a GasIf 1 mole of any chemical species contains thesame number of particles (Avogadro’s Number)AND if equal volumes of gases contain equalnumber of particles (Avogadro’s Hypothesis),then it follows that

1 mole of any gas must occupy the same volume,

if measured at the same temperature and pressure.

This volume is the “Molar Volume” and is thesame for every gas. Usually, the volume ismeasured at 25oC and a pressure of 100 kPa.(kPa = kilopascals, the normal unit formeasuring gas pressures in Chemistry.)

Mole Calculations Involving GasesThis additional knowledge opens up theopportunity to carry out quantity calculationswhich involve mass and volumes of gases.



1 mole of any gas = 24.79 litresat 25oC and 100 kPa

Example Problems1.If 15.65g of calcium carbonate (CaCO3) wascompletely decomposed by heat, what volume ofcarbon dioxide gas would be produced (ifmeasured at 25C, 100kPa)?

SolutionAlways begin with the balanced equation for thereaction.

CaCO3(s) CO2(g) + CaO(s)mole ratio = 1 : 1 : 1Moles of CaCO3: n = m = 15.65 = 0.1564 mol

MM 100.09Mole ratio is 1 : 1, so moles of CO2 formed = 0.1564

∴ Volume of CO2 = 0.1564 x 24.79 = 3.877 L (at 25C, 100kPa)

2.What volume of hydrogen gas (at 25C, 100kPa)would be produced if 10.00g of lithium metal wasreacted with sulfuric acid?

Solution2 Li(s) + H2SO4(aq) H2(g) + Li2SO4(aq)

2 : 1 : 1 : 1

Moles of lithium: n = m = 10.00 = 1.441 molMM 6.941

Mole ratio is 2:1, so moles of H2 = 1/2 x 1.441=0.7204

∴ Volume of H2 = 0.7204 x 24.79 = 17.86 L (at 25C, 100kPa)

Comparing Mass Changes When Metals Burn

Atoms always react in simple whole-numbermole ratios, but atoms have different masses,and compounds have various formulas, so theresult is that chemicals do NOT react in simpleratios by mass.

That’s why we need the mole... we measurequantities by their mass, but this makes nosense until moles are calculated.

The syllabus requires that you should considerthe mass changes involved when variousmetals combine with oxygen to form their oxidecompound.

The following table shows the mass changes for100g of the metal in each case:

100g of Formula Mass O2 Mass ofMetal of oxide needed(g) Oxide formed

Lithium Li2O 115 215

Iron Fe2O3 43 143

Zinc ZnO 49 149

Lead PbO2 15 115

Empirical & Molecular FormulasYou are reminded that a molecular formula reallydoes describe the atoms present in a molecule.

The molecular compound methane,has formula CH4, because that’s exactly what each molecule contains...1 carbon atom and 4 hydrogen atoms.

Lattice structures, either ionic or covalent are NOT molecular. Example: sodiumchloride, NaCl

The formula does NOTdescribe a molecule, but only gives the simplest ratio between thebonded atoms... this is an empirical formula.

Earlier was an example of how formulas aredetermined by analysing the mass compositionof a compound.

You should note that this method can onlyproduce an empirical formula. (In fact, the word“empirical” means something determined byexperiment, not by theory.)

If a molecular compound, with molecularformula X2Y6 was analysed by massmeasurements, its empirical formula would becalculated to be XY3... simplest ratio of atoms.

Molar Vol. ofall gases at

25C, 100kPa



1. Molar MassesCalculate the molar mass of:

a) potassium b) kryptonc) tin d) bromine (Br2)e) nitrogen gas f) magnesium oxideg) sodium iodide h) iron(III) sulfidei) ammonia j) copper(II) sulfatek) aluminium oxide l) glucose (C6H12O6)

2. No. of Moles in a Given MassHow many moles in:

a) 100.0g of lead?b) 100.0g of zinc?c) 100.0g of water ?d) 100.0g of copper(II) nitrate?e) 38.55g of magnesium fluoride?f) 60.00g of carbon dioxide?g) 1.000g of zinc oxide?h) 500.0g of glucose (C6H12O6)?i) 3.258 x 10-3g of salt (sodium chloride)?j) 128.6g of ammonium carbonate?

2. Mass Quantities in Reactionsa) Calcium burns in oxygen to form calcium oxide:

2Ca + O2 2CaOIf 8.50g of calcium reacted, what mass of calciumoxide would be formed?

b) Silver carbonate decomposes when heated:2Ag2CO3 2CO2 + 4Ag + O2

If 20.0g of silver carbonate was decomposedi) what mass of silver metal would form?ii) what mass of CO2 would be produced?iii) what mass of O2 would be formed?

c) Aluminium reacts with hydrochloric acid:2Al + 6HCl 3H2 + 2AlCl3

If 6.50g of aluminium reactedi) what mass of HCl would be consumed?ii) what mass of hydrogen gas produced?iii) what mass of aluminium chloride produced?

d) Tin reacts with steam as follows:Sn(s) + 2H2O(g) 2H2(g) + SnO2(s)

If 14.8g of tin reactedi) what mass of tin(IV) oxide would be formed?ii) What mass of steam would be consumed?iii) what mass of hydrogen would be produced?

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Worksheet 7 Masses, Moles & Particles Practice Problems Student Name...........................................

Worksheet 8 Mole Ratios & Mass in Reactions Practice Problems Student Name .........................................

3. Moles and Number of Particlesa) How many particles (atoms/molecules) in:

i) 3 moles of water?ii) 2.478 mol of CO2?iii) 5 mol of salt?iv) 0.007862 mol of copperv) 1/1000 mol of helium

b) Convert between mass, moles and no.of particles.

i) If there are 8.800x1025 atoms of tin, how many molesis this, and what would be the mass?

ii) You have a sample containing 2.575x1024

molecules of water. How many moles is this, and whatis its mass?

iii) If you weigh out 400.0g of water, how many molesis this, and how many molecules are present?

iv) If you have 2.569g of pure nickel, how many atomsare there?

v) What mass of sulfur would contain 2.500x1023

atoms?

1. Mole Ratios in Equations

Sodium reacts with water as follows:2Na + 2H2O H2 + 2NaOH

a) If 1 mole of sodium reacted, how many moles ofi) hydrogen formed? ii) water consumed?

b) If 0.25 mol of NaOH formed, how many moles ofi) sodium consumed? ii) hydrogen formed?

c) If 0.75 mole of hydrogen formed, how many moles ofi) sodium consumed? ii) NaOH produced?

Aluminium reacts with oxygen:4 Al + 3 O2 2 Al2O3

d) If 0.5 mole of Al used, how many moles ofi) Alum.oxide formed? ii) oxygen used?

e) If 0.1 mole of alum.oxide formed, how manymoles of

i) aluminium used? ii) oxygen used?

FOR MAXIMUM MARKS SHOWFORMULAS & WORKING,

APPROPRIATE PRECISION & UNITS IN ALL CHEMICAL PROBLEMS


1. A compound containing only copper andchlorine is decomposed, and the massesmeasured to find the mass composition:Mass of copper present = 12.84gMass of chlorine present = 7.16gi) Find the empirical formula.ii) Name the compound.

2. i) Find the empirical formula of a compoundcontaining carbon and hydrogen; a sample wasfound to contain 1.5g of carbon and 0.5g ofhydrogen.ii) Name the compound, given that its empiricaland molecular formulas are the same.

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Worksheet 9 Empirical Formulas Practice Problems Student Name .........................................

Worksheet 10 Reactions Involving Gases Practice Problems Student Name .........................................

3. A compound was found to contain 30%nitrogen and 70% oxygen by mass.

i) Find the empirical formula.

ii) It is later found that its molecular formula is a2 times multiple of the empirical. Write themolecular formula.

iii) Name the compound.

1. Volumes of Reacting Gases ( Assume all gases are measured at the

same temperature & pressure)

2 H2(g) + O2(g) 2 H2O(g)

a) If you used 5 litres of hydrogen, how manylitres:i) of oxygen consumed?

ii) of water vapour formed?

b) If you used 0.25 litres of oxygen, how manylitres ofi) water vapour formed?

ii) hydrogen consumed?

c) If this reaction produced 20 litres of steam,how many litres of i) hydrogen consumed?

ii) oxygen consumed?

Ammonia gas is formed by reaction of hydrogenwith nitrogen

3 H2(g) + N2(g) 2 NH3(g)

d) In order to make 9 litres of ammonia, whatvolumei) of hydrogen needed?

ii) of nitrogen needed?

e) If 0.6 litre of hydrogen reacted, what volumei) of ammonia formed?

ii) of nitrogen need?

2. Mass & Gas Volume CalculationsAll volumes measured at 25oC, 100kPa

a) To “scrub” the air and remove poisonous CO2on board the Space Shuttle, the air is continuallypumped through canisters containing 5.00kg oflithium oxide. The reaction is

Li2O(s) + CO2(g) Li2CO3(s)

i) How many moles of lithium oxide in eachcanister?

ii) How many moles of CO2 can this absorb?

iii) What volume of CO2(g) is this?

b) Iron reacts with oxygen:4Fe(s) + 3O2(g) 2Fe2O3(s)

i) If 10.0L of O2 reacted, what mass of iron(III)oxide would be formed?

ii) If 100g of iron reacted, what volume of oxygenwould be needed?

c) The electrolysis of water causesdecomposition:

2H2O(l) 2H2(g) + O2(g)

i) If 1.00g of water was decomposed, whatvolumes of each gas (measured at 25C, 100kPa)would be formed?

In an electrolysis experiment, 50mL (0.050 L) ofoxygen was produced. (at 25C, 100kPa)

ii) What volume of hydrogen (at 25C, 100kPa) wasproduced?iii) What mass of water must have beendecomposed?

Multiple Choice1.An atom of argon is about twice as heavy as an atomof neon. You would expect:A. a mole of argon to contain about half as many

atoms as a mole of neon.B. equal masses of each element to contain about the

same number of atoms.C. 2g of argon to contain about the same number of

atoms as 1g of neon.D. the molar mass of neon to be about twice the molar

mass of argon.

2.Which line shows correctly the molar mass (to thenearest gram) of the named substance?A. water, 18gB. carbon dioxide, 28gC. oxygen gas, 16gD. helium gas, 8g

3.Aluminium reacts with oxygen to form aluminiumoxide.

4 Al + 3 O2 2 Al2O3

If 1 mole of aluminium (about 27g) was to be reacted,you would need how many moles of oxygen gas?A. 0.75 mol B. 3 molC. 1 mol D. 1.3 mol

4.Avogadro’s number can be described by theabbreviation NA. If you had 2 moles of methane (CH4),then the number of hydrogen atoms present is:

A. 2 x NA B. 4 x NAC. 8 x NA D. 10 x NA

By converting between the h).......................... ofsubstances and the number ofi)..............................., it becomes possible tocalculate all the quantity relationships during achemical j).................................... From the masscomposition it is also possible to determine thek).................................. formula of compounds.

Historically, the mole concept arose from thework of 2 men: The Frenchman l).................-............................. discovered that “them)........................... of gases in chemicalreactions always show simple,n)............................... ratios to each other”. Soonafter, the Italian o)................................. suggestedthat “Equal p)......................... of all gases containq)....................... numbers of r)...........................(when measured at the same conditions ofs).............................. and ..........................)

The standard conditions usually used are apressure of t)................ and temp. of u)........oC.

25




The formal definition of the mole is “thea)...................... of atoms in 12.00 grams ofb)..................................”

One mole of any substance contains the samenumber of c)............................ The massof 1 mole of any substance is equal to itsd)................................... in grams. The actualnumber of particles in one mole of anything isknown as “e)...................................’s Number”and has a value of f).......................

In a balanced chemical equation, the “balancingnumbers” (coefficients) may be interpreted asbeing g)........................... .............................. ofreactants and products.

Worksheet 11 Mole ConceptFill in the blank spaces. Student Name...........................................

Worksheet 12 Calculations & the Mole Test Questions Student Name...........................................

5. Carbon monoxide gas reacts with oxygen gas toform carbon dioxide gas as follows:

2CO(g) + O2(g) 2CO2(g)

If 100mL of carbon dioxide was produced, then thetotal volume of reactants (all measured at the sametemp. & pressure) before the reaction would havebeen:A. 100mL B. 150mLC. 50mL D. 250mL

Longer Response Questions6. (6 marks)a) Write a balanced equation for the reaction ofaluminium metal with hydrochloric acid.b) If 6.58g of aluminium reacted fully, calculate:

i) the number of aluminium atoms involved.ii) the mass of aluminium chloride formed.

iii) the volume of hydrogen gas. (at 25C, 100kPa)

7. (4 marks)It was found by experiment that a compoundcontaining only tin and oxygen, contained 88% tin, bymass. Showing your working, determine the empiricalformula for this compound, and give its correctchemical name.

8. (4 marks)In the reaction of nitrogen and hydrogen gases toform ammonia gas, it was found by experiment that300mL of hydrogen reacted completely with 100mL ofnitrogen. 200mL of ammonia gas was produced. Allthe gas volumes were measured at a pressure of 10standard atmospheres and 150oC.

a) Write a balanced equation for the reaction.b) Explain how the experimental measurements are inagreement with Gay-Lussac’s Law.

Ores and Minerals... and now back to the metals.

Minerals are naturally occurring compounds.“Rocks” are mixtures of various minerals. Mostminerals are lattice structures, both ionic andcovalent. Some very common minerals include:

• Silica, which is chemically silicon dioxide(SiO2) and is the most common mineral onEarth. Other compounds are often included inthe silica lattice to make “silicate” minerals.These occur in virtually all rocks.• Calcite, which is calcium carbonate (CaCO3) isthe main mineral in limestone and marble.

Some minerals contain significant quantities ofmetal(s), chemically combined in the compound.

Ores are rocks and/or minerals from which it iseconomically worthwhile to extract a desired metal.

It is the economic part of this definition which iscritical. For example, there are many rocks andminerals that contain significant amounts of iron andaluminium. These are not “iron ore” or “aluminiumore” unless it is economically worthwhile to mine andprocess them to get the metal.

What Makes It Economically Worthwhile?Basically, economic feasibility is the balancebetween:

• the Commercial Price for which the metal canbe sold and• the Production Costs of mining andtransporting the ore, and chemically extractingand purifying of the metal.

Another factor is the abundance of the metaland its ores on Earth. For example, iron isrelatively cheap because it is very common inhuge deposits of iron ores.

Platinum is very rare, so it commands a highprice. This makes it worthwhile to mine evenvery low-grade ores. A low-grade iron ore wouldnot be worth mining!

The Importance of Predicting Yield from an Ore

The whole situation of economic feasibilitymakes the science of Analytical Chemistry vitalin the mining and metals industry.

Mining operations cost millions of dollars to setup. To do so, the operators need to be sure thatthe ore contains enough metal to be profitable.Chemical analysis in the laboratory is used tomeasure the mineral content of the ore body, topredict the final yield of the metal.

Ores are Non-RenewableResources

Minerals and ores have been formed overmillions and billions of years of geologicalprocesses on Earth.

Because of that time-frame, the ores are non-renewable in the sense that once we use themup, they cannot be replaced.

There is no immediate concern for running outof the most important ores, but unlimitedexploitation of any non-renewable resource is:

• irresponsible, to future generations.• unsustainable, because all non-renewable

things must eventually run out.• economically stupid, because it may be

cheaper to re-use and recycle, than to constantly extract “new” materials.

• environmentally damaging, because miningand metal smelting have a history of pollutionand ecosystem destruction.

In the not-too-distant future it may becomeeconomically worthwhile to begin “mining” theold rubbish dumps around our cities, to recoverthe discarded metals in society’s garbage.

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5. METALS FROM THEIR ORESkeep it simple science

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Case Study: Extraction of Copper from its Ores

Copper Ores include a variety ofcompounds of copper, including:

• copper(I) sulfide, Cu2S• copper(II) hydroxide mixed with

copper(II) carbonate, Cu(OH)2.CuCO3

These compounds usually occur as thin“veins” of blue-green minerals embedded in

masses of worthless silicate rock.

The copper content of the entire ore bodymight be only 3% or less. Therefore, the firststep after mining is to separate the copper

minerals from the “rock”.

Final Purification by ElectrolysisThe major use of copper is for electrical wiring. For this it needs to be 99.9% pure.

Copper is purified by electrolysis:

Chemistry of SmeltingThe concentrated copper minerals now

undergo Decomposition Reactions.

In Australia, the main copper ores containcopper(I) sulfide. If this is heated in a furnace

supplied with plenty of air the reaction is:

Copper(I) sulfide + oxygen Copper + Sulfur dioxideCu2S + O2 2Cu + SO2

The copper collected is about 98% pure.

Froth Flotation to Concentrate the OreThe ore is crushed into a powder and the copperminerals are separated from the silicates by a processof “Froth Flotation” which relies on differences in“wettability” and density.

Compressed air creates a froth of bubbles in a detergent solution.

Copper minerals, sprayed with a special oil, cling to the bubbles and are carried upwards to

overflow with the froth.

Silicate minerals are wetted by the water and, being denser, sink to the bottom.

The collected froth is then treated to separate the oil and detergent for re-use.

The ore concentrate is now about 30% copper.



Compressed air blown in tocreate a froth of bubbles

+ -

Cu+2 ionsmigrate throughCuSO4 solution

Impurities

ImpureCopper

dissolvesinto

solution

PureCopperdeposits

onelectrode

The impure copper isimmersed in CuSO4solution and electrified:

Cu Cu2+ + 2e-

The copper dissolvesinto the solution, butimpurities do not.

After migratingthrough the solution,

the ions are re-deposited as pure

copper metal on theother electrode:

Cu2+ + 2e- Cu

Sulfur dioxide is a serious pollutant if released from the smelter.

These days it is collected and used tomanufacture sulfuric acid... a useful by-pproduct.

Frothoverflows

forcollection

WasteMineralSlurry

CrushedOrein a

slurry ofwater and“wetting

oil”

Froth




28

The Case for RecyclingThe point that mineral ores are non-renewable has already been made.Eventually, any non-renewable resourcemust run out, so recycling is inevitable.

There is also a strong environmentalcase for recycling of metals, especiallyaluminium.

Extractingaluminium fromits ore requires

about 200kJ(kilojoules) ofenergy per kgof metal. This

energy ismainly in the

form ofelectricity,

which isneeded in huge

quantities forthe electrolytic

smeltingprocess.

Producing the electricity usuallyinvolves the burning of coal at a powerstation. The burning of fossil fuels likecoal is a major contributor to the“Greenhouse Effect” which manyscientists are now convinced is causingmassive climate changes to the entireEarth.

Recycling aluminium requires about 7kJof energy, a saving of about 96% inenergy and environmental impact!

Most local councils now operate “Recycling Centres” which can sort out paper,glass, plastic, etc from our garbage, as long as we remember to put recyclables in

the correct bin. Aluminium (mainly drink cans) collected this way is returned toscrap-metal businesses which clean and re-melt the metal to return it to

manufacturing industry for re-use.

Scrap Metal awaiting recycling.

Photo by Pawel Grabowski

Multiple Choice1.The “smelting” of a metal ore always involves:A. separating the metal mineral from the rock.B. decomposing a compound of the metal.C. purifying the extracted metal by electrolysis.D. all of the above.


2. (5 marks)a) Differentiate between a “mineral” and an“ore”.

b) Outline the role of Chemical Science inassessing the economic feasibility of mining amineral resource.

c) Briefly discuss the sustainability of using theEarth’s mineral resources, and outline astrategy for conservation.

3. (8 marks)a) Give the name and formula for a compoundcommonly found in copper ores.

b) Name, and briefly describe the process bywhich a copper ore is concentrated andseparated from the surrounding “rock”.

c) Write a chemical equation to describe thereaction which occurs in the smelting of the ore.(Involving the compound you named in part (a))

d) Name the process by which the smeltedcopper is purified, and relate the need forpurification to a common use of the metal.

29




“Minerals” are naturally occurringa).............................. which are mixed together inrocks.

An “ore” is a b)............................. from which itis c)................................ worthwhile to extract adesired d)..............................

Whether it is worthwhile (or not) to mine an oredepends on the balance between thee)........................................ and the f)........................................................ of mining, transportingand g)........................... the metal.

h)........................... analysis of an ore deposit isvital to predict the i)..................................... fromthe ore, to determine if it is worth mining.

Ores are j)........................................... resourcesbecause once used, they cannotk)........................................... due to the immensetime it takes for l).......................................processes to form them.

Copper ores contain compounds such asm)........................... and ......................................

After mining, the ore is crushed, thenconcentrated by “n)..................................................................”. This process uses afroth of bubbles to separate theo).............................. density copper compoundsfrom the worthless rock which is mainlyp)................................. minerals.

The “smelting” process involvesq)...................................... reactions. For a sulfideore, it reacts with r)....................... to forms)...................... metal and t).............................gas.

The final step is to u)........................... the copperby a process of v)............................................

There are many good reasons to w)......................metals, especially x)............................ whichrequires large amounts of y).................................energy to extract from its ore. Producing theelectricity required is often done by burningz).......................... fuels such as aa)......................This contributes to the “ab).................................Effect”, responsible for global climate changes.Recycling aluminium requires only a fraction ofthis energy.

Worksheet 13 Metals from OresFill in the blank spaces. Student Name...........................................

Worksheet 14 Metals from OresTest Questions Student Name...........................................

kiss metals na

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