Corrosion & its prevention

This question is about the transition metals iron and copper.

When iron rods are left out in the rain for a few weeks, the rods corrode and become covered in a brown solid.

State the name of this brown solid.

Place ticks () in boxes to show which two substances in the air react with iron to form the brown solid.

State one way to prevent the corrosion of iron rods that will be used outside.

In an experiment, 5 iron rods were left outside in the rain for a few weeks.

The mass of the iron rods was found before they were left outside and again after a few weeks.

Figure 12 shows the recorded masses.

Use this information to calculate the mean increase in mass of one iron rod.

mean increase in mass of one iron rod =_........ g

Figure 13 shows the atoms in pure gold and in a gold alloy.

State the meaning of the term alloy.

*(ii) Using Figure 13, compare pure gold and the gold alloy by

• describing how their atoms are arranged

• explaining the differences between the strength of the pure gold and the gold alloy.

Copper, iron, nickel and zinc are all metallic elements.

Which row of the table applies to copper?

Many ships are made of steel. Steel is an alloy that contains iron. Figure 4 shows blocks of zinc attached to a steel ship.

Explain how iron is protected from rusting by the zinc blocks.

Alloys of copper and nickel are used for some coins.

Figure 5 shows the relative strengths of copper and nickel and some of their alloys.

On Figure 6

• add suitable scales to the vertical and horizontal axes

• plot a graph of relative strength against percentage of nickel

• draw a curve of best fit.

A coin is made from an alloy that contains 70% copper and 30% nickel.

Determine the relative strength of this coin from your graph on Figure 6.

relative strength of the coin =_........

Explain, using Figure 6, how the percentage of nickel affects the relative strength of the alloys of copper and nickel.

A student investigated the rusting of iron rods using the following method.

step 1 find the mass of two identical iron rods

step 2 wrap magnesium ribbon around one of the iron rods

step 3 place each rod in separate boiling tubes containing 10 cm3³ of water

step 4 leave the iron rods for one week

step 5 find the new mass of the iron rods.

Figure 10 shows the apparatus used.

Figure 11 shows the results of the investigation.

Use the results in Figure 11 to calculate the percentage increase in the mass of the iron rod in boiling tube B.

percentage increase in mass of iron rod =_........

Which gas from the air has reacted with the iron rod in boiling tube B ?

The iron rod did not rust in boiling tube A.

Explain why.

*(b) Figure 12 shows some uses of copper metal.

Describe how the properties of copper metal make it a suitable material for the uses shown.

Your answer should include

• uses of copper metal shown in the photographs

• properties of copper metal including:

– chemical reactivity

– electrical conductivity

– malleability

– thermal conductivity

Steel is an alloy containing iron.

When exposed to damp air, some steels will corrode to form rust.

Which gas in the air is needed for corrosion to occur?

What type of reaction happens when the iron in steel corrodes?

Rust can be removed from steel by treating it with dilute hydrochloric acid.

One product formed in this reaction is iron chloride, FeCl₃.

Calculate the relative formula mass of this iron chloride.

(relative atomic masses: Fe = 56.0, C l = 35.5)

Figure 6 shows the composition of one type of steel that has a low resistance to corrosion and another type of steel that has a high resistance to corrosion.

Using Figure 6, state which non‑metal is in both types of steel.

Using Figure 6, state which metal is added to steel to increase its resistance to corrosion.

Explain one other way that corrosion of steel can be prevented.

A student is given two nails of the same size but made of different types of steel.

They are also given two boiling tubes and some distilled water.

Devise an experiment to show which nail corrodes more quickly.

Buildings sometimes have water sprinklers to put out fires.

The pipes in some water sprinklers are filled with nitrogen gas to prevent corrosion when the system is not in use.

State what is meant by the term corrosion.

Nitrogen can be made from sodium azide, NaN₃.

Calculate the maximum volume, in cm³, of nitrogen produced from 110 g of sodium azide.

(relative formula mass: NaN₃ = 65;

1 mol of gas occupies 24 dm³ in the conditions used)

*(b) Compare and contrast the properties and uses of pure aluminium and pure copper with the alloys of aluminium and the alloys of copper.

Include in your answer an explanation of the similarities and the differences in the properties and the uses of a pure metal and its alloy.

When iron wool reacts with oxygen from the air, the iron corrodes and iron oxide is formed.

What happens to the iron in this reaction?

A piece of damp iron wool was placed in a measuring cylinder with 50 cm³ of air, as shown in Figure 12.

Figure 13 shows the apparatus one week later.

Complete the table of results.

Use these results to calculate the percentage decrease in the volume of gas in the measuring cylinder after one week.

Not all of the oxygen in the air in the measuring cylinder has reacted with the iron.

Give a reason why.

*(c) Pure metals can be made more useful by converting them into alloys or by electroplating them.

Explain what alloying and electroplating are and how they can make metals more useful.

Hydrogen and oxygen are reactants in some fuel cells.

Which word equation shows the overall reaction that occurs in these fuel cells?

A torch contains a chemical cell. The torch is turned on and then left on for many hours.

Describe what you would see happen when the torch is turned on and then left for many hours.

A chemical cell can be made by placing two metals into an electrolyte.

Figure 3 shows how the voltage of a simple chemical cell can be measured.

A student investigated how the voltage of this cell was affected by the metal used for the rods.

Which is the only variable that should be changed in the investigation?

Explain why covering iron tools with a thin layer of grease prevents rusting.

Sacrificial protection is another way of preventing rusting.

An example of sacrificial protection is when lumps of zinc are connected to the iron-containing structure of an oil rig.

Explain how the zinc protects the iron from rusting.

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.

mass of aluminium =_........

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.

percentage by mass of magnesium in alloy

Figure 12

Describe what Figure 12 shows about the relative strength of these alloys when the percentage by mass of magnesium changes.

Determine, using Figure 12, the percentage by mass of aluminium in an aluminium‑magnesium alloy with a relative strength of 103.

percentage by mass of aluminium =_........

Metal objects can be electroplated with gold.

Give two reasons why metal objects are electroplated with gold.

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.

mass of aluminium =_........

Figure 5 shows a graph of the relative strength of aluminium-magnesium alloys when the percentage by mass of magnesium in the alloy is changed.

percentage by mass of magnesium in alloy

Figure 5

Describe what Figure 5 shows about the relative strength of these alloys when the percentage by mass of magnesium changes.

Determine, using Figure 5, the percentage by mass of aluminium in an aluminium‑magnesium alloy with a relative strength of 103.

percentage by mass of aluminium =_........

Metal objects can be electroplated with gold.

Give two reasons why metal objects are electroplated with gold.

Iron rusts when it is left in certain conditions.

Figure 9 shows the apparatus used to investigate the rusting of some iron nails.

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

Magnesium is more reactive than iron. Figure 10 shows an iron nail with a strip of magnesium wrapped around it, placed in some water. The tube was left for a few days.

State what would happen to this iron nail.

When iron rusts, a brown solid forms on the surface of the iron.

What happens to the iron as the rust forms?

Give one reason why metals are electroplated.

*(c) 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.

In a hydrogen-oxygen fuel cell, hydrogen and oxygen react at the electrodes.

The overall reaction occurring in this fuel cell is a reaction of hydrogen with oxygen.

Write the balanced equation for this reaction.

The electrodes of a fuel cell are in contact with water and air. The electrodes are made of platinum rather than iron.

State why iron is not a suitable metal for the electrodes of the cell.

Platinum acts as a catalyst.

State, in terms of its position in the periodic table, why you would expect platinum to act as a catalyst.

Some metal objects are electroplated.

State two reasons for electroplating a metal object.

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.

The method used is

• 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.

Both boiling tubes are left for a few days.

Explain why iron rod rather than stainless steel rod is used in this experiment.

State why it is not necessary to use a pipette to measure out 10 cm³ water in this experiment.

After a few days the two boiling tubes were examined.

The results are shown in Figure 5.

Explain the results of this experiment.

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.

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.

State the name of the industrial process to manufacture ammonia.

Predict the effect that adding the catalyst has on the rate of attainment of equilibrium.

Predict the effect that adding the catalyst has on the equilibrium yield of ammonia.

7 *(a) Pure metals are often converted into more useful alloys. For example, aluminium is converted into an alloy used in aircraft, iron is converted into an alloy used in cutlery and gold alloys are used in jewellery. These processes of alloying change the structures of the metals.

Some properties of pure aluminium, iron and gold are shown in Figure 12.

Explain how alloying changes these pure metals to make the alloys more suitable for the given uses.

Iron objects can corrode when exposed to the atmosphere.

Corrosion involves the oxidation of iron.

State what is meant by oxidation.

Painting iron objects prevents corrosion.

Explain why painting iron objects prevents corrosion.

Corrosion of iron objects can be prevented by painting them or by electroplating them.

State one other way of preventing the corrosion of iron objects.

The apparatus shown in Figure 13 was used to electroplate a spoon with nickel.

State to what the anode and cathode have to be connected in order to carry out the electroplating.

Predict the name of a substance that could be dissolved in water to form the electrolyte for this electroplating.

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.

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.