patterns of reactivity

© OUP: To be used solely in purchaser’s school or college

9F Patterns of reactivity

Metals and the air

The reactivity series


Metal extraction



Metals and the air


The trouble with cars...

9F The trouble with cars...

is that most cars are made of steel, which is mainly iron.

Why do we make cars out of steel?

Do you think these materials would last longer than iron?

zinc aluminium gold

plastic wood glass


9F Corrosion

Many metals react with oxygen in the air. Over time, a thin layer of metal oxide covers the surface of the metal. We call this tarnishing.

Some metals carry on reacting below the surface and their structure is destroyed. This corrosion wears away the metal.

You can prevent this by painting the metal. How does the paint stop the metal tarnishing?

Or you can choose a metal that does not react with the air – like gold.

But a gold bridge would be very expensive!


Meet the starters in the metal-corrosion Gold Cup!

9F The metal-corrosion Gold Cup

The hot favourite is potassium.Gold has poor prospects – people say it won’t run well.

Who’s your money on?

They’re under starters orders...


9F The metal-corrosion Gold Cup

Which metal corroded fastest? Which didn’t corrode at all?Were your predictions correct?


9F Keywords

Match each word or phrase with its correct meaning.

metal oxidetarnishing

unreactivepatinarusting

corrosion

a compound containing only a metal and oxygen

a metal breaking down by reacting with oxygen (and sometimes moisture)

to gather a thin layer of discoloration by reacting with the air

describes a material that does not react

a thin layer of green on the surface of copperthe corrosion of iron, which reacts with oxygen and water to form flaky iron oxide

rusting corrosionunreactive metal oxidetarnishing patina


We use the word ‘rusting’ for the corrosion of iron, since the flaky red iron oxide that forms is called rust.

TRUE!

1. Rusting is a type of corrosion reaction.2. Nitrogen from the air is the gas that iron reacts with when it starts to corrode.

3. Metals will not corrode if air and water cannot get to them.

4. All metals corrode at the same rate at the same temperature.

5. Aluminium is special because of its oxide layer.

True or False?

9F What can you trust about rust?

It’s oxygen!FALSE! Corrosion needs oxygen from the air, and sometimes water takes part in the reaction too.

TRUE! Metals corrode at different rates: the more reactive a metal is, the more quickly it will corrode.

FALSE! Aluminium doesn’t corrode because its oxide layer protects it.

TRUE!


The reactivity series



9F He’s just so reactive!

Anyone like to explain what reactivity means?Which is the more reactive atom?


What does reactivity mean?

9F Reactivity in chemistry

But an element might react very quickly with one chemical and hardly at all with another. So is it reactive or not?To compare the reactivity of different elements, we might see how easily they react with oxygen.

Some metals corrode in minutes out on the bench.

Others take longer to corrode, unless you heat them.

Elements that are reactive readily take part in reactions with other chemicals.


9F The Gold Cup again?

We can list metals in order of how quickly they react with oxygen.

This ranking of metals according to reactivity is called the reactivity series. speed of reaction with oxygen

least reactive

most reactive


What if we react different metals with acid?

9F Reaction of metals with acid

copper – no bubbles, no reaction with acid magnesium – the metal reacts quickly with the acid, producing lots of bubbles

iron – the metal reacts slowly, producing a few bubblessodium – the metal bursts into flames, a very strong reactionlead – the metal reacts very slowly, producing very few bubbles


9F What about water?

We can also rank metals by their reaction with water.Compare with the reactivity series for oxygen and acid.

The reactivity series is very useful. How can we learn it?

reactivity series withoxygen acid waterpotassiumsodiummagnesiumzincironleadcoppergold

potassiumsodiummagnesiumzincironleadcoppergold

potassiumsodiummagnesiumzincironleadcoppergold


9F Remembering the series

Come on, you can think of a better mnemonic!

metal symbol useful mnemonic?potassiumsodiummagnesiumaluminiumzincironleadhydrogencoppergold

KNaMgAlZnFePbHCuAu

KangaroosNaturallyMuckAbout inZoosForPurpleHipposChasingAardvarks


9F Test your reactivity

Put each metal in the correct box in the reactivity series.

magnesium zinciron potassium

potassium

magnesium

zinciron

sodium

aluminium

leadhydrogencoppergold


The reactivity series allows you to make predictions.

9F Using the series

Choose from the box below. What will happen when you mix...

nothing happens gas bubbles form slowlyfast reaction nothing happensvery violent reaction

...a metal …and an acid?

potassium hydrochloric acid

magnesium hydrochloric acid

iron hydrochloric acid

copper hydrochloric acid

gold hydrochloric acid

very violent reaction

fast reaction

gas bubbles form slowly

nothing happens

nothing happens


9F Feeling a bit displaced?

A displacement reaction happens when one metal replaces another one in a compound.

Magnesium is more reactive than copper.

Complete the word equation.

magnesium + copper sulphate magnesium sulphate + ?

What evidence can you see that a reaction has happened?

Magnesium displaces copper from copper sulphate solution.


9F Predicting displacement reactions

A more reactive metal displaces a less reactive one.

potassium most reactive

sodiummagnesiumzincironleadcoppergold least reactive

Magnesium displaces copper from copper

sulphate, and the blue colour disappears.

True or false?

True!

Copper displaces sodium compounds

from solution.

False!

Iron displaces gold but cannot displace

magnesium.

True!

Zinc displaces magnesium from magnesium nitrate

solution.

False!


9F A model for displacement reactions

Write a word equation for this reaction.

This model will help explain displacement reactions. Think of reactivity as aggression!


Metal extraction



9F Finding metals

All the metals we use are found in the Earth.

To extract the metal, we first dig up the ore.

The cost of a metal depends on:• how hard it is to find and dig up the ore• how reactive the metal is.

Why is the reactivity so important?

Then we carry out chemical reactions to get the pure metal out of its compound.


9F The easy ones are at the bottom

You can also find copper metal in some rocks. Sometimes you find copper oxide in ore, but it’s easy to extract.

potassiumsodiummagnesiumaluminium(carbon)zincironleadcoppersilvergold

Carbon is cheap and plentiful (as coal). If you heat copper oxide with carbon, the carbon takes the oxygen to make carbon dioxide and leaves copper metal. What sort of reaction is this?

Write a word equation for copper oxide reacting with carbon.

Gold and silver are simple to extract. You might find lumps lying around in river beds (if you’re lucky!). You just pick them up.


9F Getting tougher

The carbon takes the oxygen from the metal to make carbon dioxide. It often needs a very high temperature: about 700°C for iron.

Zinc needs a higher temperature than lead. Why?

Write a word equation to show the displacement reaction when lead oxide reacts with carbon.

Zinc, iron and lead are found in the Earth as compounds, in ores. Like copper, they can be extracted by heating with carbon.potassium

sodiummagnesiumaluminium(carbon)zincironleadcoppersilvergold


9F The downright awkward are at the top

Carbon cannot displace these elements no matter how hard you heat it. Why not?

We use electrolysis to extract these metals from their ores. An electric current passes through the molten mineral. This breaks it down so we get out the pure metal. The process is very expensive.

Potassium, sodium, magnesium and aluminium are very difficult to extract. They are very reactive. They hold on tightly to the other elements in their compounds.

potassiumsodiummagnesiumaluminium(carbon)zincironleadcoppersilvergold


Iron is less reactive. It just needs heating with carbon. Sodium needs electrolysis.

TRUE!

1. Iron is easier to extract from its ore than sodium.2. More reactive metals are more difficult to extract from their minerals than less reactive metals.

3. Gold occurs in a mineral that is difficult to break down. That is why gold is so expensive.

4. A metal that corrodes quickly will be easy to extract from its ore.

True or False?

9F Extract the truth!

Think about the ‘reactivity dog’. The scarier the dog (the more reactive the metal), the more difficult it is to remove the bone (the other elements).

TRUE! Gold often exists as the pure metal and needs no extraction. It’s expensive because it is rare.

FALSE! If a metal corrodes easily it means it is very reactive. So it will be difficult to extract.

FALSE!

patterns of reactivity

Education