AQA GCSE Chemistry

Topic Questions

GCSEChemistryAQATopic Questions3. Quantitative Chemistry3.3 Yield & Atom Economy

3.3 Yield & Atom Economy

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1a4 marks

This question is about the yield of chemical reactions.

In practice, scientists aim for a 100% yield but this is rarely achieved.

Complete the sentences to explain why a 100% yield is not achieved. 

Choose answers from the box. 

side reactions reversible  incomplete
purification transfer

 

Reactants and products can be left behind during _______________ from one container to another.

_______________ reactions can never have a 100% yield because the products are forming reactants.

A reaction might not go to completion because of _______________ or the presence of an impurity. These reactions are described as _______________ .

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1b2 marks

There are different types of yield.

The percentage yield compares the actual yield to the theoretical yield. 

Draw one line from each yield to its description.

 
aqa-gcse-3-3e-q1b-yield-definitions-

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1c1 mark

What is the correct equation to calculate percentage yield? 

Circle one equation. 

begin mathsize 14px style fraction numerator actual space yield over denominator theoretical space yield end fraction end style                    fraction numerator size 14px actual size 14px space size 14px yield over denominator size 14px theoretical size 14px space size 14px yield end fraction size 14px cross times size 14px 100                    fraction numerator theoretical space yield over denominator actual space yield end fraction cross times 100

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2a1 mark

A student completed an experiment using magnesium to displace copper from copper(II) sulfate.

Complete the symbol equation. 

Mg + CuSO4 → ________ + ________

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2b
Sme Calculator1 mark

The student added 4.8 g of magnesium to a solution of copper(II) sulfate.

Calculate the number of moles of magnesium that the student used. 

Relative atomic mass (Ar):     Mg = 24

Use the equation:

begin mathsize 14px style moles equals mass over M subscript straight r end style

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2c
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Using your answer to part (b), calculate the theoretical yield of copper. 

Relative atomic mass (Ar):     Cu = 63.5 

 
Theoretical yield of copper = ________ g

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2d
Sme Calculator2 marks

Another student completes the same experiment using 4.8 g of magnesium.

They obtain 10.16 g of copper.

What is the percentage yield of this student's experiment? 

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3a1 mark

This question is about atom economy.

What does atom economy measure?

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3b
Sme Calculator2 marks

Silver nitrate and sodium iodide can react to form silver iodide.

The equation for the reaction is:

AgNO3 (aq) + NaI (aq) → AgI (s) + NaNO3 (aq)

A student looks at the useful silver iodide product of this reaction and concludes that the percentage atom economy is 50%. 

How might the student mistakenly arrive at this conclusion?

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3c
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Calculate the relative formula mass of silver iodide, AgI. 

Relative atomic masses (Ar):     Ag = 108;     I = 127

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3d
Sme Calculator2 marks

Calculate the relative formula mass of sodium nitrate, NaNO3. 

Relative atomic masses (Ar):     N = 14;     Na = 23;     O = 16

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3e
Sme Calculator3 marks

Calculate the percentage atom economy for making silver iodide.

Use the equation: 

Percentage atom economy = fraction numerator relative space formula space mass space of space desired space product over denominator total space mass space of space all space products end fraction cross times 100

Give your answer to 3 significant figures.

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4a
Sme Calculator3 marks

Copper sulfate can be made by reacting copper oxide with sulfuric acid.

CuO + H2SO4 ⟶ CuSO4 + H2O

Calculate the percentage atom economy for making copper sulfate. 

Use the equation: 

Percentage atom economy = fraction numerator size 14px relative size 14px space size 14px formula size 14px space size 14px mass size 14px space size 14px of size 14px space size 14px desired size 14px space size 14px product over denominator size 14px total size 14px space size 14px mass size 14px space size 14px of size 14px space size 14px all size 14px space size 14px reactants end fraction size 14px cross times size 14px 100 

Relative formula masses (Mr):     H2SO4 = 98;     CuO = 79.5;     CuSO4 = 159.5

Give your answer to 3 significant figures.

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4b1 mark

Reacting copper carbonate, CuCO3, with sulfuric acid forms copper sulfate and two other products.

CuCO3 + H2SO4 → CuSO4 + H2O + CO2 

What type of reaction is this? 

Tick (✓) one box. 

Combustion  
Endothermic  
Neutralisation  
Decomposition  

 

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4c
Sme Calculator2 marks

The two methods of forming copper(II) sulfate using sulfuric acid are:

Method 1: CuO + H2SO4 → CuSO4 + H2O

Method 2: CuCO3 + H2SO4 → CuSO4 + H2O + CO2 

Which method has the highest atom economy? Explain your answer. 

Method: _____ 

Explanation: ____________________________________________________

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4d5 marks

High atom economy is a desirable attribute in industrial chemical processes.

Sort the following attributes of chemical reactions into the correct columns in Table 1.

  • Produce useful byproducts
  • High percentage yield
  • High energy costs
  • Efficient reactions
  • Use expensive raw materials

Table 1

Desirable attribute  Undesirable attribute
   
   
   

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5a
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To produce a sample of hex-1-ene, 10.2 g of hexan-1-ol is dehydrated by heating with an excess of phosphoric(V) acid.

Hexan-1-ol → Hex-1-ene + water

C6H13OH → C6H12 + H2O

After purification, 5.04 g of hex-1-ene was produced.

Calculate the number of moles of hexan-1-ol. 

Relative molecular masses (Mr):     C6H13OH  = 102;       C6H12 = 84

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5b
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Calculate the mass of hex-1-ene that could be produced.

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5c
Sme Calculator2 marks

What is the percentage yield for the production of hex-1-ene from hexan-1-ol in this experiment?

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5d
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What is the percentage atom economy for the production of hex-1-ene from hexan-1-ol in this experiment?

C6H13OH → C6H12 + H2O

Relative molecular masses (Mr):     C6H12 = 84;     H2O = 18

Give your answer to three significant figures.

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1a
Sme Calculator5 marks

In the Haber process, nitrogen and hydrogen are reacted together in conditions of high pressure and temperature to produce ammonia. 

The equation for the reaction is as follows:

N2 (g) + 3H2 (g) → 2NH3 (g)

Hydrogen is produced for the Haber process by reacting methane with steam:

CH4 (g) + H2O (g) → 3H2 (g) + CO (g)

Calculate the percentage atom economy for the production of ammonia. Give your answer to three significant figures.

 

Relative formula masses (Mr):  N2 = 28;  H2 = 2;  NH3= 17;  CH4 = 16;  H2O = 18

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1b2 marks

Explain why low pressure is used to produce the hydrogen required for the Haber process.

Give your answer in terms of equilibrium.

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1c1 mark

Figure 1 shows the percentage yield of ammonia produced at different temperatures and pressures in the Haber process.

Figure 1

percentage-yield-vs-pressure-haber-process

A temperature of 400 °C and a pressure of 200 atmospheres are used in the Haber process.

Estimate the percentage yield for the Haber Process under these conditions.

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1d
Sme Calculator4 marks

The yield of ammonia at 300 oC and 400 atmospheres is 70%. 

Calculate the mass of nitrogen, in kg, required to produce 1000 kg of ammonia under these conditions.

 N2 (g) + 3H2 (g) → 2NH3 (g) 

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2a
Sme Calculator5 marks

Iron is extracted from iron oxide in the blast furnace as shown.

2Fe2O3 + 3C → 4Fe + 3CO2 

1 tonne of iron oxide was reacted with carbon to produce 650 kg of molten iron.

Calculate the percentage yield for this reaction.

Relative atomic masses (Ar):     Fe = 56,     O = 16,     C = 12

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2b1 mark

The temperature inside the blast furnace is so high that carbon monoxide can be used to extract iron instead of carbon.

Fe2O3 + 3CO → 2Fe + 3CO2

Explain which reactant is oxidised in this reaction.

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2c
Sme Calculator3 marks

Determine if the reaction of iron oxide with carbon has a higher atom economy than the reaction of iron oxide with carbon monoxide.

Relative atomic masses (Ar):     Fe = 56,     O = 16,     C = 12

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3a2 marks

This question is about magnesium sulfate.

Calculate, to three significant figures, the percentage by mass of oxygen in magnesium sulfate.

Relative atomic masses (Ar):     Mg = 24,     S = 32,     O = 16

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3b3 marks

Magnesium sulfate can be produced by reacting magnesium with sulfuric acid.

 
Mg + H2SO4 → MgSO4 + H2
 

Write two balanced symbol equations, including state symbols, to show how magnesium sulfate can be produced by neutralisation reactions.

How did you do?

3c2 marks

Calculate the atom economy for the formation of magnesium sulfate by the reaction of magnesium and sulfuric acid. 

Relative atomic masses (Ar):     Mg = 24     S = 32     O = 16

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3d2 marks

Explain why the reaction of magnesium with sulfuric acid has a larger atom economy compared to the reactions in part (b).

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4a
Sme Calculator4 marks

Rutile is a naturally occurring ore that contains titanium oxide.

Titanium can be extracted from this ore by two different methods.

Method 1 involves the electrolysis of the ore.

TiO2 → Ti + O2 

Method 2 involves the use of a more reactive metal to displace the titanium.

TiO2 + 2Mg → Ti + 2MgO

Calculate the atom economy for each reaction. 

 

Relative atomic masses (Ar):     Ti = 48,     O = 16,     Mg = 24

How did you do?

4b2 marks

Give one advantage and one disadvantage of using Method 1 to extract titanium.

How did you do?

4c1 mark
What is the atom economy of Method 1 if the oxygen is collected and sold?
 

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4d3 marks

Titanium is used for replacement hip joints.

Give three properties of titanium that make it suitable for this use.

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5a4 marks

A student investigated two different methods to produce zinc chloride.

Method 1 is the reaction of zinc oxide with dilute hydrochloric acid.

ZnO (s) + 2HCl (aq) → ZnCl2 (aq) + H2O (l)

Describe how a sample of zinc chloride crystals could be made from zinc oxide and dilute hydrochloric acid.

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5b4 marks

A student wanted to make 15.0 g of zinc chloride using Method 1. 

Relative atomic masses, (Ar):     H = 1,     Cl = 35.5,     Zn = 65,     O = 16 

Calculate the mass of zinc oxide that the student should react with dilute hydrochloric acid to make 15.0 g of zinc chloride.

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5c
Sme Calculator2 marks

The percentage yield of the student's reaction to produce zinc chloride using Method 1 was 67.4 %.

Calculate the mass of zinc chloride the student actually produced.

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5d
Sme Calculator4 marks
Method 2 is the reaction of zinc carbonate with dilute hydrochloric acid.

 

ZnCO3 (s) + 2HCl (aq) → ZnCl2 (aq) + H2O (l) + CO2 (g)

The atom economy for Method 1 is 88.3%.

Calculate the atom economy for Method 2.

Explain the difference in the atom economies for the two methods of making zinc chloride.

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1a3 marks

Nickel oxide is reduced by heating with carbon, producing nickel metal and carbon monoxide. 

The equation for the reaction is as follows: 

NiO + C ⟶ Ni + CO

Calculate the percentage atom economy for the production of nickel.

Relative atomic masses (Ar): C = 12; Ni = 59

Relative formula mass (Mr): NiO = 75;   CO = 28

Give your answer correct to 3 significant figures.

Percentage atom economy = _____________________ %

How did you do?

1b1 mark

Magnesium can be produced by reacting magnesium oxide with silicon.

The equation for the reaction is as follows: 

Si (s) + 2MgO (s) → SiO2 (s) + 2Mg (s)

A company calculated, based on the amount of reactants and the balanced equation, that they would produce 1.2 tonnes of magnesium, but only 0.9 tonnes was made. 

Calculate the percentage yield of magnesium.

Percentage yield = __________ %

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1c2 marks

State two reasons why the calculated yield of magnesium might not be obtained.

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2a2 marks

The extraction of titanium from titanium dioxide is carried out in a two-stage industrial process:  

   Stage 1   TiO2 + 2C + 2Cl2 ⟶ TiCl4 + 2CO

   Stage 2   TiCl4 + 4Na ⟶ Ti + 4NaCl

In the stage 2 reaction the percentage yield obtained by a company was 91.2% 

The maximum theoretical mass of titanium for this batch was 12.5 kg.

Calculate the actual mass of titanium produced.

Mass of titanium = ______________________ kg

How did you do?

2b3 marks

Copper carbonate and sulfuric acid react as follows:

 

CuCO3 + H2SO4 → CuSO4 + H2O + CO2

Relative formula masses:   CuCO3 = 123.5;   H2SO4 = 98.0;   CuSO4 = 159.5

Calculate the percentage atom economy for producing copper sulfate from copper carbonate.

Atom economy = __________________ %

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2c2 marks

Give two reasons why it is beneficial for the percentage atom economy of a reaction to be as high as possible.

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3a4 marks

A student investigated the reactions of copper carbonate and copper oxide with dilute hydrochloric acid. 

In both reactions one of the products is copper chloride.

A student wanted to make 25.0 g of copper chloride by reacting copper carbonate  with dilute hydrochloric acid.

The equation for the reaction is as follows:

CuCO3 + 2HCl → CuCl2 + H2O + CO2

Relative atomic masses, Ar: H = 1; C = 12; O = 16; Cl = 35.5; Cu = 63.5

Calculate the mass of CuCO3 the student should react with dilute hydrochloric acid to produce 25.0 g of copper chloride.

Mass of copper carbonate needed = _________________________ g

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3b2 marks

The percentage yield of copper chloride was 82.2 %. 

Calculate the mass of copper chloride produced. 

Actual mass of CuCl2 produced = ____________ g

How did you do?

3c3 marks

The equations for the two reactions are shown below:

   Reaction 1:     CuCO3 (s) + 2HCl (aq) → CuCl2 (aq) + H2O (l) + CO2 (g)

   Reaction 2:     CuO (s) + 2HCl (aq) → CuCl2 (aq) + H2O (l)

   Relative formula masses:   CuO = 79.5;   HCl = 36.5;   CuCl2 = 134.5;   H2O = 18

Calculate the percentage atom economy for producing copper chloride via the second reaction.

Percentage atom economy = ________________________ %

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3d2 marks
The atom economy for reaction 1 is 68.45 %.

 

Compare the atom economies of both reactions for making copper chloride. 

State a reason for the difference.

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4a3 marks

This question is about the salt zinc sulfate.

Zinc sulfate is a compound used as a dietary supplement to treat zinc deficiency. 

 

It is also added to fertilisers, animal feeds and toothpaste. It can be made by two methods. 

The equations for the two methods are as follows: 

Method 1: ZnO + H2SO4 ⟶ ZnSO4 + H2O 

Method 2: ZnCO3 + H2SO4 ⟶ ZnSO4 + H2O + CO2 

Calculate the percentage atom economy for making ZnSO4 in Method 1 giving your answer to 3 significant figures. 

Relative formula masses (Mr):  ZnO = 81;  H2SO4 = 98;  ZnSO4 = 161;  ZnCO3 = 125

Percentage atom economy = ____________________ %

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4b5 marks

Compare the atom economy of both methods and decide which method is the most desirable.

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5a2 marks

In the Haber process, nitrogen and hydrogen are reacted together in conditions of high pressure and temperature to produce ammonia. 

The equation for the reaction is as follows: 

N2 + 3H2 → 2NH3  

Calculate the percentage atom economy for the production of ammonia.

Relative formula masses (Mr):  N2 = 28;  H2 = 2;  NH3= 17

Percentage atom economy = ____________________ %

How did you do?

5b2 marks

Figure 1 shows how the percentage yield of ammonia varies with changing conditions of pressure.

 
Figure 1

haber-process-graph-single-pressure-aqa-gcse-3-3m-q5b

Describe the trend shown in Figure 1.

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5c2 marks

Use Figure 1 to determine the difference in percentage yield at 100 atmospheres pressure and at 250 atmospheres pressure.

Difference % yield NH3 = ________ %

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6a3 marks

A scientist makes zinc iodide by reacting zinc with iodine. 

The equation for the reaction is: 

Zn + I2 ⟶ ZnI2 

Relative atomic masses (Mr): Zn = 65; I = 127 

14.5 g of zinc iodide is produced in the reaction. 

The percentage yield obtained is 93.0%.

What is the maximum theoretical mass of ZnI2 produced in this reaction?

Maximum theoretical mass = ____________________ g

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6b1 mark

Suggest a reason why the percentage yield is not 100%.

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