Unit 9F

Patterns of Reactivity

Learning outcome

Explain the process of tarnishing and state the scientific name for it

Carry out an experiment to place certain metals in order of reactivity

Tarnishing

What is tarnishing?

Look at the pictures below

In all of these images the metal has reacted.

What have they reacted with?

In the laboratory this process can be speeded up by adding heat – i.e. burning.

Most metals react with oxygen (tarnish) – but they may do so in very different ways. Some react faster than others and some may not react at all.

The reaction of a metal with oxygen is scientifically called

CORROSION.

All metals corrode but the corrosion of iron (and it’s alloys) has a special name – RUSTING.

Using corrosion to determine reactivity

We will now carry out an experiment to determine the reactivity of 3 metals.What we will need:

•Iron filings

•Copper turnings

•Magnesium strips

•Bunsen burner

•Tongs

•Crucible

•Tripod stand

Using corrosion to determine reactivity

What we will do:

1. Light the Bunsen burner

2. Using the tongs hold a piece of magnesium in the hot part of the flame.

3. Observe

4. Now put some iron turnings in to the crucible

5. Roast on a tripod stand

6. Observe

7. Repeat with the copper turnings

Reaction with oxygen - observations

Copy the table below and add your observations

The iron filings glowed red and sparkled leaving a brown-black looking solid.

Iron

The copper turnings went through reds and oranges and then slowly got a permanent coating of black.

Copper

The ribbon burned with a dazzling white flame giving grey-white smoke and ash.

Magnesium

They are all forming metal oxides.

Look at your observations and put these three metals in order of reactivity with oxygen - magnesium, copper, iron.

1.

2.

3.

magnesium

iron

copper

Activity

Reaction with oxygen - equations

The equations are:

magnesium oxideoxygen+magnesium

2Mg + O2 2MgO

copper oxideoxygen+copper

2Cu + O2 2CuO

iron oxideoxygen+iron

4Fe + 3O2 2Fe2O3

Learning outcome

Describe the reactions of metals in water and create a reactivity series

Observing reactions with water

Some metals (like lead and copper) react only slowly with water. The word plumbing comes from plumbum (Latin for lead) because the ancient Romans used lead for their water pipes.

However, even lead does slowly dissolve and it is very poisonous. Because of this plumbers don’t use lead any more. (Should we re-name them coppers!)

Modern pipes – not lead but copper or plastic

Reaction with water

No reactionSilver

No reactionCopper

No rapid reaction but gradual conversion of the iron to rust

Iron

This is, of course, relevant to the use of copper for plumbing and of silver and of gold for jewellery.

No reactionGold

Reaction with water - observations

Potassium immediately produced a lilac flame as it skimmed around making a fizzing noise.

Potassium

The sodium melts and skims over the surface producing a stream of small bubbles. Sometimes a yellow-orange flame appeared.

Sodium

Bubbles of hydrogen gas are given off quite quickly. The neutral water becomes alkaline.

Calcium

All the metals are reacting to form metal hydroxides and hydrogen gas.

Other metals reaction with water

Watch the demonstration with the alkali and alkali earth metals

Why are alkali metals stored under oil?

http://www.youtube.com/watch?v=m55kgyApYrY

Put the following metals in order in terms of their reaction with water.

Iron, sodium, potassium, silver, copper, calcium, gold

1.

2.

3.

4.

5

potassium

sodium

calcium

iron

Copper, silver, gold

Activity

Reaction with water – equations

Equations for these reactions are:

hydrogen+lithium hydroxide

water+lithium

2Li + 2H2O 2LiOH + H2

hydrogen+sodium hydroxide

water+sodium

2Na + 2H2O 2NaOH + H2

hydrogen+potassium hydroxide

water+potassium

2K + 2H2O 2KOH + H2

Learning outcome

Describe the reactions of metals in acid and create a reactivity series

Observing reactions with acid

The very first chemists were called alchemists. They spent much of their time trying to find methods of changing cheap metals into gold. Some were very good at making metals look gold.

But gold is so un-reactive that it wont dissolve even in really strong acids. Other metals do.

• This became known as “the acid test” because it stopped tricksters making false claims that something was gold.

• We still use the phrase “the acid test” to mean something that will show up fakes.

Most metals dissolve in strong acid – but gold doesn’t

Experiment

What you need… 4 test tubes Test tube stand 0.1M HCl Safety glasses Pieces of

•Copper

•Magnesium

•Lead

• iron

What to do….. Add a small amount

of each metal to the bottom of a test tube

Half fill the test tube with acid

Observe the reaction

Acids and metals

Reaction with acid

Metal Cold Acid (HCl) Hot Acid (HCl)

Magnesium Fizzed rapidly -

Aluminium - Bubbled quickly

Copper No reaction No reaction

Iron No reaction Slow bubbling

Lead No reaction Occasional bubble

Calcium Really fast -

Zinc Moderate Bubbling

-

Match up the metals listed with the correct photo.Copper, magnesium, iron, zinc

copper Magnesium iron zinc

All the reactions involve the formation of a salt and hydrogen gas.

Activity

Reaction with acid - equations

Here are equations for some of the reactions

hydrogen+magnesium chloride

hydrochloric acid

+magnesium

Mg + 2HCl MgCl2 + H2

hydrogen+aluminium chloride

hydrochloric acid

+aluminium

2Al + 6HCl 2AlCl3 + 3H2

hydrogen+zinc chloridehydrochloric acid

+zinc

Zn + 2HCl ZnCl2 + H2

Reaction with acid - equations

Here are equations for some of the reactions

hydrogen+magnesium chloride

hydrochloric acid

+magnesium

Mg + 2HCl MgCl2 + H2

hydrogen+aluminium chloride

hydrochloric acid

+aluminium

2Al + 6HCl 2AlCl3 + 3H2

hydrogen+zinc chloridehydrochloric acid

+zinc

Zn + 2HCl ZnCl2 + H2

Reaction with acid – more equations

We get similar equations with sulphuric acid

hydrogen+magnesium sulphate

sulphuric acid+magnesium

Mg + H2SO4 MgSO4 + H2

hydrogen+aluminium sulphate

sulphuric acid+aluminium

2Al + 3H2SO4 Al2(SO4)3 + 3H2

hydrogen+zinc sulphatesulphuric acid+zinc

Zn + H2SO4 ZnSO4 + H2

And with nitric acid…

hydrogen+magnesium nitrate

nitric acid+magnesium

Mg + 2HNO3 Mg(NO3)2 + H2

hydrogen+aluminium nitrate

nitric acid+aluminium

2Al + 6HNO3 2Al(NO3)3 + 3H2

hydrogen+zinc nitratenitric acid+zinc

Zn + 2HNO3 Zn(NO3)2 + H2

Reaction with acid – more equations

Learning outcome

Predict and create a reactivity series of metals using previous evidence

Explain displacement

Based on the reactions with acid, put the metals magnesium, aluminium, copper, iron, lead, calcium, zinc in order of reactivity (most reactive first).

1 5

2 6

3 7

4

calcium

magnesium

aluminium

zinc

iron

lead

copper

Activity

The Activity Series

We can combine all the information from the reactions with air, water and acid to get an overall activity seriesactivity series.

With Oxygen

magnesium

iron

oxygen

With water

potassium

sodium

lithium

With acid

calcium

magnesium

aluminium

zinc

Iron

Lead

copper

More complete studies give us the activity series shown on the next slide.

The Reactivity Series

Incr

easi

ng r

eact

ivity

Potassium

Sodium

Calcium

Magnesium

Aluminium

Zinc

Iron

Lead

Copper

Silver

Gold

Please

Send

Charlies

Monkeys

And

Zebras

In

Lead

Cages

Securely

Guarded!

One way of helping to remember this order is to learn the silly sentence:

Make your own mnemonic to help you learn the Reactivity series!!

The Activity Series - uses

We can use the activity series to make predictions about reactions we have not yet been able to try out.

This will apply both to simple reactions of the metals with oxygen, water and air.

It will also apply to more complex reactions where one metal is competing with another.

Learning outcome

Use the reactivity series to predict displacement reactions

Displaced metals

Displaced persons is an old-fashioned word for refugees: people who have lost their homes and possessions - often as a result of wars.

In chemistry we sometimes have displaced metals. These are metals that have lost a competition.

To start with such metals are bonded to a non-metal as part of a compound.

Along comes a more reactive metal and takes the non-metal away.

+

Can you predict what will happen?

Metal React with

Prediction

gold acid

calcium water

sodium oxygen

Silver oxygen

zinc oxygen

Potassium

Sodium

Calcium

Magnesium

Aluminium

Zinc

Iron

Lead

Copper

Silver

Gold

No reaction

fizzing

Burns vigorously

Very slow reaction

Burns moderately

Activity

Activity Series – displacement reactions

We get situations where two metals are competing to be combined with a non-metal or non-metal group like nitrate or sulfate.

In such cases the more active metal wins the competition. E.g.

copper+magnesium chloride

copper chloride

+magnesium

• The more reactive magnesium displaces the less reactive copper to “win” the chloride.

• What will happen in this reaction?

No reactionmagnesium chloride

+silver

Displacement Reactions - predictions

We can predict what will happen if we add metals to solutions of various metal sulphates in the table.

For example,

copper+magnesium sulphate

copper sulphate

+magnesium

Metal/ Solution

MgSO4 ZnSO4 FeSO4 CuSO4

Magnesium

Zinc

Iron

Copper

= reacts = no reaction

Copper s

ulphat

e

Iron s

ulphat

e

Zinc

sulp

hate

Mag

nesiu

m s

ulphat

e

1. The solutions are added to a dip tile .

Mg Mg Mg

Zn Zn Zn

Fe Fe Fe

Cu

Cu

Cu

2. Pieces of metal are added to each dip.

3. Reaction either does or does not take place.

4. Can you predict the outcomes?

Mg Mg Mg

Zn Zn Zn

Fe Fe Fe

Cu

Cu

Cu

Activity

Displacement Reactions - photos

1. Same reactions can, of course be carried out on a larger scale

Reaction between copper sulphate and magnesium.

Why does the blue copper sulphate colour gradually disappear?

The copper in the copper sulphate is turning into red copper metal.

Magnesium

copper+magnesium sulphate

copper sulphate

+magnesium

Mg + CuSO4 MgSO4 + Cu

zinc+magnesium sulphate

zinc sulphate+magnesium

Mg + ZnSO4 MgSO4 + Zn

iron+magnesium sulphate

iron sulphate+magnesium

Mg + FeSO4 MgSO4 + Fe

Zinc

No reactionmagnesium sulphate

+Zinc

Zn + MgSO4 - -

iron+zinc sulphateiron sulphate+Zinc

Zn + FeSO4 ZnSO4 + Fe

copper+zinc sulphatecopper sulphate

+Zinc

Zn + CuSO4 ZnSO4 + Cu

Iron

No reactionmagnesium sulphate

+iron

Fe + MgSO4 - -

No reactionzinc sulphate+iron

Fe + FeSO4 - -

copper+iron sulphatecopper sulphate

+iron

Fe + CuSO4 FeSO4 + Cu

Copper

No reactionmagnesium sulphate

+copper

Cu + MgSO4 - -

No reactionzinc sulphate+copper

Cu + FeSO4 - -

No reactioncopper sulphate

+copper

Cu + CuSO4 - - -

Copy the table below

Solution

Metal

Copper

Sulphate

Iron Sulphate

Magnesium Sulphate

Zinc Sulphate

Copper

Iron

Magnesium

Learning Outcome

Explain how less reactive metals are extracted

Describe the process used to extract more reactive metals