5.1 Transition Metals, Alloys & Corrosion

Pure iron is mixed with carbon and other metals to make alloys.

Explain, using the arrangement of metal particles, why iron alloys are stronger than pure iron.

A stainless steel contains 0.10% carbon, 16.4% chromium, 19.8% nickel, 4.2% molybdenum and iron.

Calculate the percentage of iron in the alloy.

Calculate the mass of molybdenum contained in a 30 g sample of this alloy.

State why stainless steel, rather than pure iron, is used to make cutlery.

A student wanted to investigate what variables affect rusting.
They set up the three test tubes shown in Figure 1.
They left the tubes for five days.

Figure 1

For each test tube, predict if you think the nail will rust.

Give a reason for each prediction.

The student set up test tube A again but this time used a painted nail.

Explain why painting a nail will protect it from rusting.

Aluminium forms a layer of aluminium oxide on its surface.
This protects it from corrosion.

Write a balanced symbol equation for this reaction.

Other than its corrosion resistance, give one reason why aluminium is a good choice for making window frames.

Iron is a transition metal.
Iron is used to build bridges.

Evaluate using iron for this function.

Iron objects can be covered with a layer of zinc to protect them from rusting.

Name this process.

If a zinc-covered nail is scratched, the nail is still protected by sacrificial protection.

Explain how this works.

Higher Only

During sacrificial protection zinc is oxidised to form zinc ions.

Write the half equation to show this.

Higher Only

A teacher used the apparatus in Figure 2 to explain how electroplating works.

Figure 2 

The half equation for what happens at the copper rod is:

Cu → Cu²⁺ + 2e^-

What type of reaction is this?

Give a reason for your answer.

Higher Only

Explain what you would see happen to the iron nail.

Include a half equation in your explanation.

Higher Only

Explain why the colour of the copper sulfate solution does not change during the experiment.

Give one reason why electroplating is used.

Transition metals are located in the middle of the periodic table and have certain properties.

Which two properties do most transition metals have? 

Alloy steels are made when iron is alloyed with other transition metals such as cobalt and chromium.

Which row of the table shows the typical properties of a transition metal?

Figure 1 shows the chain on a bicycle.

Figure 1

Explain how lubricating the chain with oil prevents corrosion of the steel chain.

Iron fences can be galvanised by coating them with a layer of zinc.
When the layer of zinc is scratched exposing the iron to the weather, the iron does not rust.

Explain why the exposed iron does not rust.

Metals have high melting points.

Explain, in terms of their structure and bonding, why metals have high melting points.

Many metals corrode.

When a metal corrodes

An experiment is carried out to see if magnesium ribbon wrapped around a piece of iron rod has an effect on the rate at which the iron rod rusts.

The apparatus is shown in Figure 4.

• an iron rod, with magnesium ribbon wrapped around it, is placed in a boiling tube labelled A
• 10 cm³ water from a measuring cylinder is poured into this boiling tube
• an identical rod but with no magnesium ribbon wrapped around it is placed in a second boiling tube labelled B
• 10 cm³ water from a measuring cylinder is poured into this boiling tube.

(1)

Hydrazine, N₂H₄, reacts with oxygen.

A metal in water corrodes faster than an identical piece of metal in the same volume of water containing dissolved hydrazine.

Use the information to explain how hydrazine slows corrosion.

Higher Only

Ammonia is used to make hydrazine.

In the industrial process to manufacture ammonia, nitrogen and hydrogen are combined in the presence of an iron catalyst.

N₂ + 3H₂  2NH₃ 

Nitrogen and water are produced when ammonia reacts with oxygen. 

A metal oxide catalyst is used to speed up the rate of reaction.

Which of the following metal oxides would most likely be used for this reaction?

Transition metals have many uses.

The pie chart in Figure 6 shows the uses of one transition metal.

Figure 6

Calculate the percentage of this transition metal used in construction.

percentage of this transition metal used in construction = ..................................................

Figure 7 shows five statements about iron.

Put ticks () in the boxes in Figure 7 to show which statements are true and which statements are false.
The first one has been done for you.

	true	false
iron is a poor conductor of heat
iron can act as a catalyst
iron forms compounds that are coloured
iron has a low density
iron has a very high melting point

Figure 7

Most iron produced is converted into alloys of iron.

mass of molybdenum = ................................................. g

Many transition metals are used to make the reactants in chemical cells.

Figure 8 shows a graph of the voltage produced by a chemical cell as it is used in a torch for many hours.

Suggest an explanation for the shape of the graph.

Iron rusts when it is left in certain conditions.

Figure 9

Explain why the iron nail in tube A would rust but the iron nails in tubes B and C would not rust.

(3)

Figure 10

State what would happen to this iron nail.

(1)

Give one reason why metals are electroplated.

The pure metals aluminium, copper and gold and the alloys brass and magnalium are used to make many useful articles.

The way in which these metals and alloys are used is related to their properties, such as their density, electrical conductivity, resistance to corrosion and strength.

State some uses of aluminium, copper, gold, brass and magnalium and explain how each use is related to their properties.

Brass is an alloy of which metals?

Alloys of gold are often used to make jewellery.
The purity of gold is measured in carats.
Different alloys of gold have different carats.

Figure 2 shows the relationship between the purity of gold in carats and the percentage of gold in the alloy.

A necklace with a mass of 5.0 g was found to contain 2.9 g of gold.

Determine the purity of the gold necklace in carats.
Show your working.

Higher Tier Only 

A gold ring contains 3.94 g of gold.

Calculate the number of gold atoms in the ring.
(relative atomic mass: Au = 197,
Avogadro constant = 6.02 × 10²³)

Show your working.

number of gold atoms = ...........................................

Why are alloys harder than the pure metals from which they are made?

This question is about the metal gold.

(1)

(1)

A gold alloy contains 78% gold by mass.

Calculate the mass of gold in 2.00 kg of this alloy.

Give your answer in grams.

mass = .............................................................. g

A substance used to purify gold is kept in a container.

There are some hazard symbols on the container.

Draw one straight line from each hazard symbol to its meaning.

Some gold alloys contain copper.

Copper reacts with oxygen when heated.

copper + oxygen → copper oxide

A teacher calculates that 1.20g of copper reacts completely with oxygen to form 1.50g of copper oxide.

A student heats 1.20g of copper pieces in a container.
Then they heat 1.20g of copper powder in another container.
After heating, the mass of the solid in the containers is found.

The results are shown in Figure 7.

Figure 7

Explain the observations and give reasons why the masses after heating are less than expected.

Aluminium alloys are used instead of pure aluminium in aircraft manufacture.

Explain, in terms of the arrangement of metal particles, why aluminium alloys are stronger than pure aluminium.

A 695.0 g sample of an aluminium-magnesium alloy contains 2.00% by mass of magnesium.

Calculate the mass of aluminium in this sample.

Figure 12 shows a graph of the relative strength of aluminium-magnesium alloys
when the percentage by mass of magnesium in the alloy is changed.

Figure 12

(2)

Metal objects can be electroplated with gold.

Give two reasons why metal objects are electroplated with gold.

Complete the sentence on corrosion.

When a metal corrodes

Higher Only

Objects made from transition metals are sometimes coated with a thin layer of another transition metal to improve their appearance and to protect against corrosion.

The voltage of a cell is 1.5V.

Give a reason why this voltage of the cell decreases when the cell is left connected in a circuit.

Duralumin is an alloy of aluminium and copper.

The radii of the aluminium and copper atoms are shown in Figure 11.

Figure 11

Explain why copper added to aluminium to form the alloy makes the alloy stronger than pure aluminium.

Gold is often alloyed with other metals when it is used to make jewellery.

The proportion of gold in a piece of gold jewellery is measured in carats.

Pure gold is 24 carats.

A 9 carat gold ring has a mass of 12 g.

Calculate the mass of gold in this ring.