CIE IGCSE Chemistry

Topic Questions

IGCSEChemistryCIETopic Questions4. Electrochemistry4.2 Applications of Electrolysis

4.2 Applications of Electrolysis

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1a1 mark
Hydrogen and oxygen react together to form water.

Complete the word equation for this reaction:

hydrogen   +   ____________________   →   water

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1b2 marks

The reaction between hydrogen and oxygen is used in hydrogen fuel cells.

Complete these sentences about hydrogen fuel cells using words from the list.

reduction combustion electricity
     
temperature change gas oxidation


Water is produced when hydrogen undergoes .......................................................

This causes the fuel cell to produce  ..................................................

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1c3 marks

The diagram below shows a hydrogen fuel cell.
aqa-gcse-5-2e-tq3c-hydrogen-fuel-cell


Complete the table to show the functions each of the substances perform in a hydrogen fuel cell using words from the list.

electrolyte electrode waste product
     
source of oxygen fuel anode

Substance Function
Potassium hydroxide solution  
Hydrogen  
Water  

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1d2 marks

Extended Only

Give two advantages of using hydrogen fuel cells compared with using petrol engines to power motor vehicles.

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2a1 mark

The diagram below shows a fuel cell.

fuel-cell

Hydrogen can be used as the fuel.

Complete the balanced symbol equation for the reaction that occurs in a hydrogen fuel cell.

___ H2   +   O2   →   ___ H2O

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2b1 mark

Extended Only

The graph below shows the reaction pathway diagram for the reaction of hydrogen and water in a hydrogen fuel cell.

reaction-profile-v-to-z

Which of the labels represents hydrogen and oxygen? 

Tick one box.

V  
   
W  
   
X  
   
Y  
   
Z  

How did you do?

2c1 mark

Extended Only

Which of the labels in the reaction pathway diagram in part (b) represents water? 

Tick one box.

V  
   
W  
   
X  
   
Y  
   
Z  

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2d2 marks

Extended Only

The first vehicle powered by a hydrogen fuel cell was built in 1966 by General Motors. It could travel at up to 70 mph in 30 seconds. 

Suggest two disadvantages of using a hydrogen fuel cell in a car.

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3a1 mark

Separate: Chemistry Only

An application of electrolysis is electroplating.

Which of the these statements about electroplating is correct?
Tick one box.

It is used to extract metals from their ores  
   
It is a process used to break down a substance using heat  
   
It is used to coat the surface of one metal with a layer of a different metal  
   
It is a method of sacrificial protection  



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3b3 marks

Separate: Chemistry Only

The diagram shows the equipment needed to electroplate a metal spoon with silver. 

Complete the labels in the boxes using words from the list.

anode power supply electrolyte
     
electrolysis cathode  

fTV0_z57_4-2-3b-e-electroplating-diagram-a

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3c1 mark

Separate: Chemistry Only

Which one of these substances would be a suitable electrolyte when plating an iron spoon with silver?
Tick one box. 

Silver  
   
Iron  
   
Silver nitrate  
   
Iron(II) nitrate  

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3d1 mark

Separate: Chemistry Only

Give one change that would need to be made to the equipment in part (b) to coat the metal spoon with nickel instead of silver.

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4a3 marks

Chemistry Only

A student wanted to use electrolysis to electroplate an object with nickel.

Match the part of the apparatus used for electroplating on the left with its correct identity on the right.

electroplating-parts

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4b1 mark

Chemistry Only

Which of the following equations shows the correct half-equation for the reaction that occurs at the cathode?
Tick one box.

Ni2+ → Ni + e–  
   
Ni + e– → Ni2+   
   
Ni2+ + 2e– → Ni   
   
Ni + 2e– → Ni2+   

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4c1 mark

Chemistry Only

What occurs at the anode, oxidation or reduction?

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4d2 marks

Chemistry Only

Which two of the reasons about why objects are electroplated are correct.
Tick two boxes.

It improves the appearance of the object  
   
It is more expensive  
   
It increases the melting point of the object  
   
It makes the object more resistance to corrosion  
   
It makes the object harder  

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5a2 marks

Separate: Chemistry Only

A student wants to electroplate objects made out of different materials.

Which of the following materials would not be suitable for electroplating?
You may tick more than one box.

Glass  
   
Copper  
   
Poly(ethene)  
   
Iron  

How did you do?

5b1 mark

Separate: Chemistry Only

The student sets up the following equipment to electroplate an iron rod with nickel.

4-2-5b-e-incorrect-electroplating-diagram

What error did they make when setting up the equipment?
Tick one box.

The solution should contain iron ions  
   
The circuit should contain a switch  
   
Both electrodes should be made from iron  
   
The strip of nickel and iron rod are connected to the   
wrong terminal of the power supply  

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5c1 mark

Extended Only

In a different experiment, copper was used to electroplate a metal spoon. This was the half-equation on the surface of the spoon.

Cu2+ + 2e– → Cu

Explain how this equation shows that copper is reduced.

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5d1 mark

Separate: Chemistry Only

Which of the following substances could be used as the electrolyte when electroplating an iron spoon with copper?
Tick one box.



an iron rod  
   
aqueous iron nitrate  
   
a copper rod  
   
aqueous copper nitrate   



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1a1 mark

A fuel cell produces electrical energy by the oxidation of a fuel by oxygen.
The fuel is usually hydrogen but methane and methanol are two other fuels which may be used.
A diagram of a hydrogen fuel cell is given below in Figure 1.

hydrogen-fuel-cell

Figure 1

When the fuel is hydrogen, the hydrogen is oxidised to form water, which is the only product.

Suggest what additional product would be formed if methanol was used.

How did you do?

1b1 mark

Give the chemical equation for the reaction that takes place in a hydrogen fuel cell.

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1c2 marks

Extended Only

In a hydrogen fuel cell, hydrogen loses electrons at the anode.

Write the half equation to show the reaction at the anode.

How did you do?

1d
Sme Calculator3 marks

Extended Only

Hydrogen and oxygen can also react in a combustion reaction forming water vapour.

Calculate the mass of water vapour produced when 500 cm3 of hydrogen combusts in excess oxygen.


Mass of water vapour ...................................... (g)

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2a3 marks

Extended Only

The Gemini and Apollo moon probes use hydrogen fuel cells to generate an electric current and do not need to be electrically recharged. The product of this reaction can be used to supplement the drinking water for astronauts.

Deduce the half equations for the reactions at each electrode in a hydrogen fuel cell, and then the overall equation for the hydrogen-oxygen fuel cell, to show the product used to supplement drinking water.

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2b1 mark

A hydrogen fuel cell is an electrochemical device that converts chemical energy into electrical energy. A continuous supply of fuel is supplied to one electrode and a continuous supply of air is supplied to the other electrode.

Suggest why a fuel cell does not need to be recharged.

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2c2 marks

Extended Only

The General Motors Electrovan was built in 1966. It was the first vehicle powered by a hydrogen fuel cell and could travel at up to 70 mph for 30 seconds.

Suggest two environmental advantages of using a hydrogen fuel cell rather than an internal combustion engine.

How did you do?

2d1 mark

Extended Only

Hydrogen fuel cells are commonly considered to be carbon neutral by the general public because they do not release any carbon dioxide or other greenhouse gases when they are used. This is not technically correct.

Suggest why hydrogen fuel cells cannot be classed as carbon neutral.

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3a2 marks

Separate: Chemistry Only

Electrolysis can be used to silver-plate metal cutlery.

Give two reasons why metal cutlery is sometimes silver-plated.

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3b4 marks

Separate: Chemistry Only

The apparatus used to electroplate a metal spoon with silver is shown. The apparatus has not been set up correctly.

 
CkgdjNgX_4-2-3b-h-incorrect-silver-plating-a-spoon
 

The metal spoon erodes and a thin layer of copper forms on the pure silver electrode.

Explain two changes that should be made to this apparatus in order to be able to silver plate the metal spoon. 

How did you do?

3c1 mark

Separate: Chemistry Only

Suggest why it is difficult to electroplate a plastic object.

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4a1 mark

Hallmarked precious metals such as gold, silver, platinum and palladium are often plated on jewellery. It is usually cheaper to have plated jewellery than solid pieces made from these heavy, expensive and precious metals.

A base metal, often copper or nickel, is manipulated into the desired shape for the piece of jewellery. The precious metal is then plated onto the piece of jewellery.

Give the name used to describe the electroplated base metal.

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4b
Sme Calculator3 marks

Around 85% of female wedding rings are 1.5 - 2.5 mm wide. The depth of a female wedding ring depends on the shape of the ring. The dimensions of a flat profile ring are shown.

 
4-2-4b-h-ring-dimensions
 

With wedding rings, electroplating to a depth of 8 microns (0.008 mm) is considered thick plating.

 
i)
Calculate the cross-sectional area of:
  • an average female, flat profile wedding ring.
  • an average female, flat profile wedding ring with thick plating.
 
[2]
 
ii)
Calculate the percentage of the ring that is plating.
 
[1]

How did you do?

4c
Sme Calculator2 marks

Extended Only

Most wedding rings contain between 4 and 6 g of metal. Wedding rings that are 18-carat gold are plated with gold that contains 750 parts per 1000 of gold.

Using your answer to part (b), calculate the number of moles of gold that is required to plate an average wedding ring with 18-carat gold.

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4d2 marks

Separate: Chemistry Only

The wedding ring can be electroplated using the apparatus shown.

 
4-2-4d-h-electroplating-a-ring-a
 

Label the anode and the cathode on the diagram. Explain your answer in terms of gold ions.

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5a1 mark

Extended Only

Electroplating is generally done for decorative purposes or for protection.

Food cans are generally made from three different materials:

  • aluminium
  • tin-coated steel / tinplate
  • electrolytic chromium coated steel
4-2-5a-h-food-tin-cans
 

Explain why aluminium food cans do not need to be electroplated.

How did you do?

5b3 marks

Extended Only

Tin-coated steel food cans and electrolytic chromium coated steel food cans that contain acidic foods can bulge as shown. The bulging is a result of a redox reaction inside the can forming a gas.

 
4-2-5b-h-bulging-food-can
 
i)
Give the ionic equation forming the gaseous product during the reaction between the metal food can and the acidic food.
 
[1]
 
ii)
Explain how this shows that there is a break in the tin coating or chromium plating.
 
[2]

How did you do?

5c1 mark

Separate: Chemistry Only

Common electroplated gifts used to include items such as jewellery, jewellery boxes, shaving kits, cutlery, hip flasks, candlesticks and other ornamental pieces.

More recent developments in electroplating mean that plastic and organic items, such as the rose shown, can be metal plated.

 
silver-plated-rose
  

Plastic and organic items are sprayed or coated with a fine film to allow electroplating to occur.

Name a material that the film must contain. Explain your answer.

How did you do?

5d2 marks

There are a number of steps in the process of gold-plating a rose.

  • Surface Cleaning
  • Surface Preparation
  • Electro Cleaning and Steam Cleaning
  • Water Rinse
  • Flashing / Striking
  • Applying Base Coat
  • Electroplating
  • Final Rinse and Drying
  • Final Polish

During the flashing / striking step, a thin layer of high-quality nickel is plated on to the rose. This step improves the bonding between the rose and the gold-plating due to the electrical conductivity of the nickel.

Suggest another reason for applying a thin layer of nickel. Explain your answer. 

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1a3 marks

Separate: Chemistry Only

Electroplating steel objects with silver involves a three-step process.

electroplating-steel
step 1   A coating of copper is applied to the object.
step 2   A coating of nickel is applied to the object.
step 3   The coating of silver is applied to the object.

A diagram of the apparatus used for step 1 is shown.

The chemical process taking place on the surface of the object is

Cu2+ (aq) + 2e– → Cu (s)

i)
Explain whether this process is oxidation or reduction.

[1]

ii)
Explain why the concentration of copper ions in the electrolyte remains constant throughout step 1.

[2]

How did you do?

1b2 marks

Separate: Chemistry Only

Give two changes which would be needed in order to coat nickel onto the object in step 2.

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1c3 marks

Copper, nickel and silver are transition elements.

Typical physical properties of transition elements are a high density and a high melting point.

Give three different properties of transition metals which are not typical of other metals.

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2a1 mark

A fuel cell produces electrical energy by the oxidation of a fuel by oxygen.
The fuel is usually hydrogen but methane and methanol are two other fuels which may be used.
A diagram of a hydrogen fuel cell is given below.

hydrogen-fuel-cell

When the fuel is hydrogen, the only product is water.

What additional product would be formed if methane was used?

How did you do?

2b1 mark

Write the equation for the chemical reaction that takes place in a hydrogen fuel cell.

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2c2 marks

Extended Only

Fuel cells are used to propel cars.

Give two advantages of a fuel cell over a gasoline-fuelled engine.

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3a4 marks

Chromium is a transition element.
 

i)
Predict two differences in the physical properties of chromium and sodium.

[2]
ii)
Predict two differences in the chemical properties of chromium and sodium.
[2]

How did you do?

3b8 marks

Chromium is used to electroplate steel objects. The diagram shows how this could be done.

electroplating-steel-2-

i)
Give two reasons why steel objects are plated with chromium.

[2]
ii)
The formula of the chromium(III) ion is Cr3+ and of the sulfate ion is SO42–. Give the formula of chromium(III) sulfate.

[1]
iii)
Write the equation for the reaction at the negative electrode (cathode).
 
[2]
iv)
A colourless gas, which relights a glowing splint, is formed at the positive electrode (anode). Name this gas.
[1]
v)
During electrolysis, it is necessary to add more chromium(III) sulfate but during copper-plating using a copper anode, it is not necessary to add more copper(II) sulfate. Explain. 
 
[2]

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4a4 marks

Separate: Chemistry Only

Metal objects can be electroplated with silver.

Describe how a metal spoon can be electroplated with silver.
Include:

  • what to use as the positive electrode and as the negative electrode
  • what to use as the electrolyte
  • an ionic half-equation to show the formation of silver.

You may include a diagram in your answer.

How did you do?

4b1 mark

Separate: Chemistry Only

Give one reason why metal spoons are electroplated with silver.

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5a2 marks

Extended Only

Some cars use hydrogen–oxygen fuel cells as a source of energy.

Explain one advantage to the environment of using a hydrogen–oxygen fuel cell instead of a petrol engine.

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5b1 mark

Extended Only

Fuel cells can be used with alternative fuels. One alternative fuel is the liquid fuel, methanol, CH3OH.


Suggest an advantage of using methanol instead of hydrogen in a fuel cell to power vehicles.

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5c4 marks

Extended Only

When methanol reacts with oxygen in a methanol-oxygen fuel cell, carbon dioxide and water are produced. Draw the reaction pathway diagram for the reaction on the axes below.

Label the following:

  • reactants
  • products
  • activation energy
  • overall energy change

2-4m-q2c-reaction-pathway-diagram

How did you do?

5d2 marks

Write the balanced symbol equation for the reaction between methanol and oxygen in a methanol-oxygen fuel cell.

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