C2 exam questions

1. Structures and bonding2. Structures and properties3. How much?4. Rates and energy5. Salts and electrolysis

Chapter 1- structures and bonding

1. What is a compound?2. How can you observe if a chemical reaction has occurred or not?3. What part of an atom is involved in bonding?4. How many electrons can the first energy level/shell hold?5. How many electrons can the second energy level/shell hold?6. If an atom gains electrons, what does it become?7. If an atom loses electrons, what does it become?8. What is the overall charge of an ionic compound?9. How are the atoms in a metal held together?10. What is metallic bonding?11. Describe ionic bonding.12. The atoms in group 1 form +1/+ ions. What to the atoms in group 2, 6

and 7 form?13. Metals for m___________ ions and non-metals form __________

ions14. What is covalent bonding- describe it in detail.

1. Two or more elements chemically bonded together2. bubbles/fizzing, colour change, temperature change or a precipitate (solid) is formed3. electrons

4. Two 5. Eight

6. A negative ion.An ion is a CHARGED ATOM BECAUSE IT HAS EITHER LOST OR GAINED ELECTRONS7. A positive ion8. It is zero!9. The metallic bond is the force of attraction

between these free electrons and metal ions.10. The metal atom loses its outer shell electrons to become a positive ion. The force of attraction between the electrons (neg) and the positive ions.

11. Ionic bonds form when a metal reacts with a non-metal. Metals form positive ions (because the donate their electron to the non-metal atom); non-metals form negative ions (because they gain an electron from the metal atom). So now both the metal atom and the non-metal atom are ions as they have less/more electrons than they normally do. Ionic bonds are the electrostatic forces of attraction between oppositely charged ions.

12. Group 2 = + 2 ionsGroup 6 = -2 ions (it is easier to gain two than lose 6)Group 7= -1 ions (gain one more to get a full outer shellGroup 8= do not form ions as they have a full outer shell

13. Metals form positive ions (lost electrons) and non-metals form negative ions (gain electrons)14. Shared pair of electrons (in the exam you must say all of this statement to gain two marks).

It occurs between two non-metals to form a covalent molecule. It is their outer electrons that are shared.

proton + (1)

neutron 1

electron - (1)

2.8.3

24

electron -(1)

1 0

proton +(1)

protons

electrons

protons

neutrons

4

9

sodium........ positive or +

chloride... negative or –

positive

any reference to loss of electrons

for 1 mark

reference to charge being +2 (in (a)) or to loss of 2

electrons (in (b))

for 1 mark

covalent bonds

any reference to shared electrons

gains 1 mark

but idea that bond is shared pair of

electrons

gains 2 marks

element

compound

an / one electron from the sodium atom

is lost / transferred to form a sodium ion

because oppositely charged ions attract each

other

or

because chloride ions are negative and sodium

ions are positive

13

14

4

nucleus

it has 2 more neutrons or converse

or

O-16 has 8 neutrons (1 mark)

O-18 has 10 neutrons (1 mark)

because ammonia is made of small molecules

/ simple

molecules / simple molecular structures

1

and so there are weak forces between the

molecules

1

or

and so the intermolecular forces are weak

incomplete answers that link only size of

molecule or strength of intermolecular forces

with boiling point only gain 1 mark

can be from diagram chlorine (2.8).7.

accept chlorine needs one more electron

1

can be from diagram shares a pair of electrons

1

shared pair of electrons is a covalent bond

do not accept ionic bond

1

can be from diagram and appropriately annotated sodium (2.8). 1.

and chlorine (2.8).7

1

sodium loses one electron and chlorine gains one electron

1

Na+ and Cl– formed

1

bond formed between oppositely charged ions or ionic bond

is formed

do not accept covalent bond

1

same element

different number of neutrons

same number of protons and electrons

4 mark question

• the layers / atoms can slide over each

other

• because there are only weak /

intermolecular forces (of

attraction) / bonds between layers

• graphite conducts electricity because the

electrons are

delocalised or electrons free

• this is because each carbon / atom is

joined / bonded to

three other carbon / atoms or each carbon

forms 3 bonds /

one electron on each carbon is not used for

bonding

in pure copper the atoms are arranged in layers

accept a correct diagram

1

therefore copper is soft because copper atoms can slide over each

other

1

in bronze the tin atoms disrupt / distort the structure

accept a correct diagram

1

therefore bronze is harder than copper because the metal atoms

cannot slide over each other

1

Carbon dioxide

4

A

because nano-sized particles are smaller than

normal sized particles

may cause harm when they are inside the

body

the sodium atom loses / transfers an / one

electron

1

the chlorine atom gain(s) this / an / one

electron

1

involves electrons in the outer energy levels /

shells of

both the sodium atom and the chlorine atom

1

sodium chloride has a giant structure / lattice

of oppositely

charged ions / positive and negative ions

1

the electrostatic forces of attraction / bonds

between ions

are strong

1

therefore sodium chloride has a high melting

point because a

large amount of energy is needed to make the

ions mobile

1

increase (owtte) or gets hotter

ignore gives out heat / takes in heat

CH4

4 mark question

any four points from:

• high melting point owtte

ignore boiling point

• many or all atoms joined together

• each silicon (atom) joined to four oxygen (atoms) or

each oxygen joined to two silicon

• covalent (bonds)

• many bonds would need to be broken

• strong bonds

allow hard to break bonds

• lot of energy / heat needed to break bonds

allow high temperature needed to break bonds

• giant / macromolecular / lattice / diamond structure

• unreactive

allow doesn’t react with materials within furnace = 1 mark

• rigid / hard structure

• no free electrons

• poor conductor of heat

2.8.3 on diagram as Xs / dots

any two from:

• electrons in highest energy level or

electrons in outer shell

• electrons are delocalised or sea of

electrons

• electrons are free or electrons move

around / flow

• electrons carry charge / current

H2 + Cl2 → 2HCl

MgCl2

because magnesium chloride is made of ions

or is ionic

accept there are strong forces of attraction

between the ions / particles in MgCl2 or strong

electrostatic attractions

accept more energy to separate particles in

MgCl2

answers apply to:

accept diagrams and/or descriptions

carbon dioxide CO2

ammonia NH3

methane CH4

water H2O

*outer electronic structure of one atom correct or needs

correct number of electrons to complete outer shell

1

*outer electronic structure of other atom correct or needs

correct number of electrons to complete outer shell

1

*one shared pair of electrons (as one covalent bond)

use of ions or reference to ionic bonding negates this mark

1

*outer electronic structure of compound correct or each atom now

has a full outer shell/noble gas electron structure

1

5 mark question

calcium atom loses two electrons

accept diagrams with correct labelling

1

(each) fluorine atom gains one electron

accept two electrons transfer from a calcium atom to the

two fluorine atoms for these first two marks

1

forming full (outer) shells of electrons

accept forming full (outer) energy levels or noble gas

electronic structures

1

giving the ions Ca2+ and F-

1

attraction between ions of opposite charges

any (must be named)

F2

–/F–

covalent

electrons

covalent

made of small molecules:

usually gas or liquid ) dependent on

have low melting points ) having first

have low boiling points ) point above

forces between molecules are weak

C16 H34

electron

gains 1 mark

but shared electrons

gains 2 marks

Group 2 / Alkaline Earth Metals

MgCl2/Mg2+ (Cl–)2

(or equation with correct answer)

for 1 mark

ionic / electrovalent

covalent/description of covalent

forces/bonds between the molecules/particles

(not atoms) are weak

some electrons from outer shells

(some electrons) free to move/mobile

through whole structure/between atoms/sea

of electrons

hold atoms together

for 1 mark each

or positive ions in a sea of electrons (owtte)

2 marks

atoms in regular structure/layers

giant structure

close packed

credit diagrams – look for labels

electrons,

free to move

layers/atoms can slide over each other

free electrons hold atoms strongly

together/strong forces of attraction/bonds

(between atoms)/tight packing of atoms

made of layers

of carbon atoms

weak forces of attraction between layers

(owtte) / weak

vertical bonds i.e.

candidate refers to the diagram

layers can slide over each other

layers peel off

because there are electrons

which are free (to move)

reason for free electrons / each carbon atom

has 3 covalent bonds

8 electrons in outer shell

accept anywhere in outer shell

accept dots or crosses

1

negative sign outside bracket

1

(metal) atom / ion

electron

free electrons or electrons move

1

(allow metal) atoms / ions to slide over each

other

OR

bonding non - directional for 2 marks

any two from

• large numbers of covalent bonds

allow giant lattice / structure

• between atoms

do not accept between molecules

• (covalent) bonds strong

accept need much energy to break

lithium + water � hydrogen + lithium hydroxide

any three from:

one / the carbon (atom)

reject molecules once

four hydrogen (atoms)

shape / properties neutral

CH4

hydrocarbon

saturated / single bond

covalent bond / shared electrons

alkane

1

weak forces

accept weak bonds

1

between molecules / intermolecular

reject intramolecular

1

Chapter 2- structures and properties

1. Describe how ionic compounds form giant ionic lattices.2. Why do ionic substances conduct electricity when moltenor in

solution but not when solid?3. What are the two types of covalent structures?4. Describe simple covalent molecules 5. Describe giant covalent structures6. Describe giant metallic structures7. What is a polymer?8. How are polymers formed?9. What is the difference between thermosoftening and

thermosetting polymers?10. What is nanoscience?11. What is a nanoparticle?12. What are the advantages and disadvantages of nanoscience?

1. bonding: between a metal and a non-metal which lose and gain electrons respectively to form an ionic compound. Held together by strong electrostatic forces of attraction between positive ions and negative ions. Structure: forms a regular structure known as a giant ionic lattice.

2. Because it is only when they are molten or in solution do they have free electrons, therefore can carry charge and conduct electricity4. Covalent bonding: shared pair of electrons Simple covalent structure properties:a) DON’T CONDUCT ELECTRICITY: no free electrons and no

ions so they don't conduct electricity.b) LOW MELTING AND BOILING POINTS: This is because the

weak intermolecular forces break down easily.

Hydrogen, ammonia, methane and water are also simple molecules with

covalent bonds. All have very strong bonds between the atoms, but much

weaker forces holding the molecules together. When one of these

substances melts or boils, it is these weak 'intermolecular forces' that break,

not the strong covalent bonds. Simple molecular substances are gases,

liquids or solids with low melting and boiling points.

3. Simple molecules and giant covalent structures.Simple molecules consist of a small number of atoms joined by covalent bonds. For example, water and carbon dioxide exist as simple molecules The covalent bonds joining the atoms together in a simple molecule are strong. However, the intermolecular forces between simple molecules are weak.

5. Giant covalent structures contain a lot of non-metal atoms, each joined to adjacent atoms by covalent bonds. The atoms are usually arranged into giant regular lattices - extremely strong structures because of the many bonds involved. The graphic shows the molecular structure of diamond and graphite: two allotropes of carbon, and of silica (silicon dioxide).PROPERTIES: a) Very high melting and boiling points: because a lot of strong

covalent bondsb) ONLY SOME CONDUCT ELECTRICITY- e.g. graphite- because

it has free electrons.Examples: diamond, graphite, silicon dioxide, Buckminsterfullerene

6. Metals form giant structures in which electrons in the outer shells of the metal atoms are free to move. The metallic bond is the force of attraction between these free electrons and metal ions. Metallic bonds are strong, so metals can maintain a regular structure and usually have high melting and boiling points.Metals are good conductors of electricity and heat, because the free electrons carry a charge or heat energy through the metal. The free electrons allow metal atoms to slide over each other, so metals are malleable and ductile.

7. Many monomers bonded together8. Polymers have properties which depend on the chemicals they are made from, and the conditions in which they are made. For example, poly(ethene) can be low-density or high-density depending upon the catalyst and reaction condition used to make it

9. Thermosoftening polymers soften when heated and can be shaped when hot. The shape will harden when it is cooled, but can be reshaped when heated up again. Poly(ethene) is a thermosoftening polymer. Its tangled polymer chains can uncoil and slide past each other, making it a flexible material. Thermosetting polymers have different properties to thermosoftening polymers. Once moulded, they do not soften when heated and they cannot be reshaped. Vulcanised rubber is a thermoset used to make tyres. Its polymer chains are joined together by cross-links, so they cannot slide past each other easily.

10. A nanometre, 1 nm, is one billionth of a metre (or a millionth of a millimetre). Nanoparticles range in size from about 100 nm down to about 1 nm. They are typically the size of small molecules, and far too small to see with a microscope.Properties and uses of nanoparticlesNanoparticles have a very large surface area compared with their volume, so they are often able to react very quickly. This makes them useful as catalysts to speed up reactions. They can, for example, be used in self-cleaning ovens and windows.Nanoparticles also have different properties to the same substance in normal-sized pieces. For example, titanium dioxide is a white solid used in house paint and certain sweet-coated chocolates. Titanium dioxide nanoparticles are so small that they do not reflect visible light, so cannot be seen. They are used in sun screens to block harmful ultraviolet light without appearing white on the skin.

11. Very tiny particles/nanoparticles range in size from about 100 nm down to about 1 nm.12. Nanoparticles are used in products that are currently available.sports equipment: nanoparticles are added to materials to make them stronger whilst often being lighter. They have been used in tennis rackets, golf clubs and shoesclothing: silver nanoparticles have been added to socks. This stops them from absorbing the smell of sweaty feet as the nanoparticles have antibacterial propertieshealthcare: nanoparticles are used in sunscreens. They offer protection and can be rubbed in so there are no white marks.Harmful effectsThere are some concerns that nanoparticles may be toxic to people. They may be able to enter the brain from the bloodstream and cause harm. Some people think more tests should take place before nanoparticles of a material are used on a wider scale.

layers / lattice / giant structure / regular

pattern of atoms (diagram)

allow layers / lattice / giant structure / regular

pattern of ions

do not accept particles

1

outer (shell) electrons

accept valence electrons

1

(free to) move (through whole structure)

accept delocalised / mobile / free

1

3 mark question

covalent

four

hard

three

soft

electron

any three from

• (is a) giant structure/lattice structure

• crystalline / hard

accept just 'crystals(s)’

• high melting point / solid

• high boiling point

• conductor (of electricity) when dissolved

in water

or conductor (of electricity) when ions are free

to move

• conductor (of electricity) when molten

• soluble in water

4 mark question

heat

1

then mould / extrude into a new shape /

object

1

plastic made of polymer chains that can move

(when heated)

1

because plastic / polymer has weak

intermolecular forces

1

hard

carbon dioxide

because nano-sized particles are smaller than

normal-sized particles

1

may cause harm when they are inside the

body

any two from:

• (new) computers

• (new) catalysts

• (new) coatings

• highly selective sensors

• stronger / lighter

construction materials

small or few atoms thick or size in the range 1–

100 nanometres

sensible idea of passing through smaller gaps owtte

eg can pass through skin / pores / cells or more easily absorbed

there are delocalised electrons / free electrons

/ electrons

which move within the aluminium / metallic

structure

1

therefore these electrons are able to carry the

current / charge

1

any two from:

• good at absorbing UV light / radiation

• spread more easily

• cover better

• save money / use less

• transparent

• less chance of getting skin cancer or

stops skin cancer

toxic to (cells / specific cells)

1-100 nm in size

or

a few (hundred) atoms in size

accept very / really small / tiny

C3H8

reduce wear of metal ie don’t get damaged

or other sensible answer

or

stop / reduce friction

accept stop metal heating up

accept move more smoothly

ignore make it slippery / rub more smoothly

or

prevent seizing

layers (of atoms)

1

can slide / slip over each other

allow slip off

or

weak forces of attraction / weak bonds (between layers)

intermolecular forces / bonds

1

are weak

(covalent) bonds are weak = 0

or

forces between molecules or bonds

between molecules (1)

(attractive) forces are weak = 1

are weak (1)

to check the safety of the perfume (owtte)

accept references to possible harmful /

dangerous effects of perfume or possible

reactions on skin

eg to show it does not damage skin / cause

cancer etc.

allow to see what it smells like on the skin

allow so the company do not have to test on

animals

fertilisers

nitrogen

accept N or N2

Chapter 3- How much?1. What is the mass of a proton, neutron and electron?

2. What is the charge of a proton, neutron and electron?

3. What is the mass number and atomic number of Na?

4. What is the difference between relative atomic mass (Ar) and relative formula mass (Mr)

5. What is the percentage of magnesium in magnesium oxide. The Ar of Magnesium is 24 and the Ar of O is 16.

6. What is the difference between empirical formula and molecular formula of a compound?

7. What is a mole?

8. How can you calculate moles?

9. What is a reversible reaction? Give an example.

10. What are food additives and how can we identify them?

11. Describe methods of instrumental analysis to detect substances in a sample mixture

1. proton= 1, neutron= 1, electron= 1/1849 (0.0005)2. proton= +, neutron= 0, electron= -!

3. Na- mass number= 23, atomic/proton number= 11 4. Relative atomic mass is of the element (Ar) e.g. Na, the Ar= 23, Cl, the Ar= 35.5. Relative formula mass (Mr) of NaCl is (23+ 35.5= 58.5)

5.

Mr of MgO= (24+16)= 40Ar of Mg is 24.Percentage of magnesium in magnesium oxide= 24/40= 60%

6. Empirical formula is the simplest form of the molecular formula. For example,

Molecular formula: C6H12

Empirical formula: CH2 (divided by 6)

7. One mole is a substance contains 6.02 x 1023

This number is known as the Avogadro constant.9. In a reversible reaction, the products can react to produce the original reactants again.For example,

ammonium chloride ammonia + hydrogen chloride

The equation shows that ammonium chloride (a white solid) can break down to form ammonia and hydrogen chloride. It also shows that ammonia and hydrogen chloride (colourless gases) can react to form ammonium chloride again.

10. A food additive is a substance added to food to make it look or taste better. The food additives that are legal to use in Europe are given E numbers. Paper chromatography can be used to detect substances in food. It works because some compounds dissolve better than others in particular solvents and so they travel up the paper differently and can therefore be compared. Instrumental analysis is faster and more accurate than paper chromatography.

11. Instrumental analysis- Many substances are made up of a mixture of compounds.- So scientists have thought of a way called gas-chromatography and

mass spectrometry to separate the substances.- First they use gas chromatography to separate substances (like paper

chromatography but the substances need to be vaporised (turned into gas)

- Then pass the separated substances through a mass spectrometer so the elements and compounds can be identified. The pattern of peaks it produces will help you identify what the element or compound is.

157

correct answer with or without working

(2 × 19 + 119) for 1 mark only

allow (119 + 19 =) 138 for 1 mark only

ignore units

160 ignore units

(2 × 56) + (3 × 16) for 1 mark

70

700

measure volume / mass of gas produced (1)

in a certain time period

or measure decrease in mass of flask and

contents at regular time intervals (1)

or time taken for the mass to decrease by

certain amount (1)

349

RFM

160

112

70

neutralisation/acid base reaction

17 (tonnes)

give 80 (tonnes) (even if only in working)

for 1 mark each

320 (tonnes) or alternative method)

3 marks for correct answer

(if 17 and 80 not given allow 1 mark for correct

answer using their figures)

correct named instrumental method

eg

atomic absorption spectroscopy / spectrometry

accept atomic / absorption spectroscopy

accept aas

or

mass spectrometry / spectroscopy

accept mass spec

or

infrared (spectrometry) / IR

or

ultraviolet / spectroscopy / UV

or

nuclear magnetic spectroscopy / nmr

or

gas-liquid chromatography / GLC

any one from:

• fast / quick or comment about speed

ignore lost

ignore human error

• small amount

accept operators do not need chemical skills

• sensitive / accurate / precise

ignore safe / easier to use

• ease of automation

• reliable / efficient

• can be left to run / continuous analysis

144

accept TiCl4 = 190 for 1 mark

accept another correct step in calculation

eg 570/190 = 3 for 1 mark

1000 × 1000 / 0.065

gains 1 mark

but

15384615g (accept answer rounded to

minimum of 2 sig. figures)

(accept answer with no units or correct units

but incorrect unit loses one mark)

(answer correctly worked out in kg is

acceptable)

gains 2 marks

Empirical formula

4 mark question

C H O

0.60 0.15 0.40

12 1 16

= 0.05 = 0.15 = 0.025

2 6 1

C2H6O

Chapter 4- Rates of reaction1. What do we mean by the rate of a chemical reaction?2. How can we measure the rate of a chemical reaction in the lab?3. What affects the rate of chemical reaction?4. What is the collision theory?5. How does surface area affect the rate of a chemical reaction?6. How does temperature affect the rate of a chemical reaction?7. How does a catalyst affect the rate of a chemical reaction?8. How does concentration affect the rate of a chemical reaction?9. What is the difference between an exothermic and endothermic

reaction?10. What happens in the energy transfers in a reversible reaction?11. How can we use the energy from exothermic reactions?12. How can we use the cooling effect of endothermic reactions?13. What are the advantages and disadvantages of each type of hand

warmer.

1. The phrase ‘rate of reaction’ means ‘how fast is the reaction’ or 'the speed of the reaction'.

2. It can be measured as the 'rate of formation of product' (e.g. collecting gaseous product in a syringe) or the 'rate of removal of reactant'. The speeds of reactions are very varied.

3. - Temperature- Surface area- Pressure - Concentration - Use of a catalyst

4. For a chemical reaction to occur, the reactant particles must collide. But collisions with too little energy do not produce a reaction.The particles must have enough energy for the collision to be successful in producing a reaction.The rate of reaction depends on the rate of successful collisions between reactant particles. The more successful collisions there are, the faster the rate of reaction.

5. Surface area:If a solid reactant is broken into small pieces or ground into a powder: - its surface area increases- more particles are exposed to the other reactant- there are more collisions- the rate of reaction increases

6. temperature:If the temperature is increased: - the reactant particles move more quickly- they have more kinetic energy- the particles collide more often, and more of the collisions result in a reaction- the rate of reaction increases

7. catalyst:A catalyst is a substance that can increase the rate of a reaction. The catalyst itself remains unchanged at the end of the reaction it catalyses. A catalyst speed up the rate of a chemical reaction by lowering the activation energy (the minimum amount of energy needed to start a chemical reaction).

8. concentration:If the concentration of a dissolved reactant is increased, or the pressure of a reacting gas is increased: the reactant particles become more crowdedthere is a greater chance of the particles collidingthe rate of reaction increases

9.Exothermic reactionsThese are reactions that transfer energy to the surroundings. The energy is usually transferred as heat energy, causing the reaction mixture and its surroundings to become hotter. The temperature increase can be detected using a thermometer. Some examples of exothermic reactions are:burningneutralisation reactions between acids and alkalisthe reaction between water and calcium oxideEndothermic reactionsThese are reactions that take in energy from the surroundings. The energy is usually transferred as heat energy, causing the reaction mixture and its surroundings to get colder. The temperature decrease can also be detected using a thermometer. Some examples of endothermic reactions are:electrolysisthe reaction between ethanoic acid and sodium carbonatethe thermal decomposition of calcium carbonate in a blast furnace

10. Reversible reactions are where the products can react to remake the original reactants. If the forward reaction is exothermic, the reverse reaction is endothermic.The decomposition of ammonium chloride is a reversible reaction:ammonium chloride ammonia + hydrogen chlorideAmmonium chloride decomposes when it is heated, so the forward reaction is endothermic - energy must be transferred from the surroundings for it to happen. The backward reaction is exothermic -energy is transferred to the surroundings when it happens.

11. Exothermic reactions can be used for everyday purposes. For example, hand warmers and self-heating cans for drinks (such as coffee) use exothermic reactions.

12. Endothermic reactions can be used for everyday purposes. For example, certain sports injury cold packs use endothermic reactions.13. The disposable hand warmer lasts longer when activated than the

reusable warmer. However, it can only be used once. The opposite applies to the re-usable hand warmers.

because this is an endothermic reaction

1

that takes in energy from the surroundings as

the ammonium

nitrate dissolves

1

any two from:

• A has four colours(*)

• B has three colours(*)

(*) if first two bullets not stated

accept A has more colours (than B) or B has less colours (than

A) for 1 mark only

• A / B have two colours the same

• B has one different colour

drinks / colours B and C are safe

1

drinks / colours A and D are not safe

1

use of solvent / solution / water / any named solvent

1

separates / carries colour(s) / dye(s)

allow any idea of movement

eg runs / moves

1

match against Rf value / known chromatogram / similar pattern

or comparison to permitted additive / colour

removal of coloured additive from salmon does not gain any marks

ignore reasons for separation

maximum 2 if technique clearly doesn’t work

1

any three from:

accept colour 3 is a mixture of colours 1 and 2 for 3 marks

• colour 1 is made up of only one colour / dye

• colour 2 is made up of only one colour / dye

• colour 3 is made up of two colours / dyes

or

more colours (than colours 1 and 2)

• colours 1, 2 and 3 are all different

• colour 1 is less dark than colour 2

gives out

heat

chromium and aluminium oxide

chromium oxide

oxygen removed/gains electrons

Chapter 5- salts and electrolysis

1. What is the difference between an acid and an alkali?2. What is the difference between an alkali and a base?3. Give examples of acidic products.4. Give examples of alkali products.5. Give an example of a substance that is neutral.6. What is a state symbol?7. How can we test the pH of a substance?8. What ions do all acids form when we add them to water?9. What ions do all alkalis form when we add them to water?10. Metal + acid � ______ + ________11. Acid + base/alkali � ___________ + _________12. What is electrolysis?13. How is aluminium obtained from aluminium oxide? Why is

cryolite used in the process?14. What is produced in the electrolysis of brine?15. Why do we electroplate objects?

1. Acids have a pH below 7 and alkalis have a pH above 72. Alkalis and bases both neutralise acids. If a base does dissolve in water, we call it an alkali.

3. Vinegar (ethanoic acid)Fizzy drinks (carbonic acids)Tea (tannic acid)In the lab: sulphuric acid and hydrochloric acid

4. Drain cleanerBleach Sea water

5. Water

Symbol Meaning

(s) solid

(l) liquid

(g) gas

(aq) aqueous (dissolved in water)

7.Litmus paper:red litmus: stays red if acid, stays red is neutral, turns blue if alkali.Blue litmus: stays blue if alkali, stays blue if neutral, turns red is acidic

Universal indicator

pH meter (most accurate)

8. H + ions9. OH- ions

10. MASH

METAL+ ACID� SALT + HYDROGEN

11. ACID + BASE � SALT + WATER

12. Splitting of a compound using electricity13. By electrolysis:• aluminium oxide (bauxite) is melted / made liquid• aluminium ions are attracted to the negative electrode• at the negative electrode aluminium is formed oraluminium ions gain electrons• oxide ions are attracted to the positive electrode• oxygen is formed at the positive electrode or oxideions lose electrons

• the oxygen reacts with carbon to make carbon dioxide orcarbon dioxide formed at positive electrode.

Aluminium oxide has a very high melting point (over 2,000°C), so it would be expensive to melt it. Instead, it is dissolved in molten cryolite, an aluminium compound with a lower melting point than aluminium oxide. The use of cryolite reduces some of the energy costs involved in extracting aluminium.

14.Brine is a solution of sodium chloride (NaCl) and water (H2O). The process of electrolysis involves using an electric current to bring about a chemical change and make new chemicals. The electrolysisof brine is a large-scale process used to manufacture chlorinefrom salt. Two other useful chemicals are obtained during the process, sodium hydroxide (NaOH) and hydrogen (H2).It is important that the chlorine and sodium hydroxide produced in the process are separated they react when they come into contact with each other. Chorine: disinfectant (swimming pools)Sodium hydroxide: manufacture of paperHydrogen: manufacture of hydrochloric acid and potential as a pollution-free fuel

15.Electrolysis is used to electroplate objects. This is useful for coating a cheaper metal with a more expensive one, such as copper or silver.How it worksThe negative electrode should be the object that is to be electroplatedThe positive electrode should be the metal that you want to coat the object withThe electrolyte should be a solution of the coating metal, such as its metal nitrate or sulfateHere are two examples.Electroplating with silverThe object to be plated, such as a metal spoon, is connected to the negative terminal of the power supply. A piece of silver is connected to the positive terminal. The electrolyte is silver nitrate solution.

hydroxide

nitric

Mg MgSO4 H2

to remove the (excess) magnesium

breakdown / decomposition / splits into elements (1)

using electricity (1)

lead bromide melted / free ions

(+) bromine

(–) lead

substance brokendown / separates / splits into elements

by electric current / electricity

ions free to move e.g. when molten / in solution

allow 1 mark for “a substance that conducts electricity”

hydrogen (ion)

H+

neutralisation

NaOH HCl NaCl H2O

Nitric acid

Potassium hydroxide water

6 mark question

examples of the chemistry points made in the response

• aluminium oxide is melted / made liquid

• aluminium ions are attracted to the negative

electrode

• at the negative electrode aluminium is formed or

aluminium ions gain electrons

• oxide ions are attracted to the positive electrode

• oxygen is formed at the positive electrode or oxide

ions lose electrons

• the oxygen reacts with carbon to make carbon

dioxide or

carbon dioxide formed at positive electrode.

6 mark question

examples of the chemistry points made in the

response

• aluminium oxide is melted / made liquid

• aluminium ions are attracted to the

negative electrode

• at the negative electrode aluminium is

formed or

aluminium ions gain electrons

• oxide ions are attracted to the positive

electrode

• oxygen is formed at the positive

electrode or oxide

ions lose electrons

• the oxygen reacts with carbon to make

carbon dioxide or

carbon dioxide formed at positive electrode.

H2SO4 or red (acidic) pH < 7

accept names of compounds

accept correct use of acidic

1

NaOH or purple (alkaline) pH > 7

alkaline and neutral without any mention of

pH for 1 mark only

1

NaCl or green (neutral) pH 7

ignore high or low pH

1

nitric (acid)

accept HN03

sodium hydroxide / caustic soda / NAOH

negative ions move to the positive electrode etc.

/because it is negative

/opposite charges attract

loss of electrons

chloride ions lose electrons to form chlorine

Cl– – e– → Cl

1

hydrogen ions gain electrons to form hydrogen

H+ + e– → H

1

sodium hydroxide remains in solution

Na + and OH– remain in solution to form sodium hydroxide

1

bulb lights up

bubbles / fizz / gas or chlorine given off

in solid, ions

1

are not free to move / (charged) particles

cannot move or converse

atoms / electrons cannot move worth 0 marks

breakdown / decomposition / splitting up (1)

not separation

by using electricity (1)

gas A = chlorine / oxygen

1

deposit B = copper

any one from:

• manufacturer of chlorine / sodium

hydroxide / hydrogen / sodium

• electroplating of steel / reference to

plating

not galvanising

• extraction of aluminium / metal

reactivity series specified

• purification of copper

not making copper

H+(aq) + OH– (aq) → H2O(l) or

H3O+(aq) + OH–(aq) → H2O(l)

nitric acid and ammonia (solution)