Yield & Atom Economy (AQA GCSE Chemistry): Exam Questions

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 (A_r): C = 12; Ni = 59

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

Give your answer correct to 3 significant figures.

Percentage atom economy = _____________________ %

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 = __________ %

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

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

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 = __________________ %

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

A student wanted to make 15.0 g of zinc chloride. The equation for the reaction is:

ZnCO₃ + 2HCl →  ZnCl₂ + CO₂ + H₂O

What mass of zinc carbonate should the student add to the hydrochloric acid to make 15.0 g of zinc chloride?

Relative atomic masses (A_r): C = 12    Zn = 65   O= 16    Cl = 35.5     H= 1

A student made zinc chloride by reacting 15.0 g of zinc carbonate with hydrochloric acid.

ZnCO₃ + 2HCl →  ZnCl₂ + CO₂ + H₂O

The percentage yield of zinc chloride was 82.4%.

Calculate the mass of zinc chloride the student actually produced.

Relative atomic masses (A_r): C = 12    Zn = 65   O= 16    Cl = 35.5     H= 1

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 (M_r):  N₂ = 28;  H₂ = 2;  NH₃= 17

Percentage atom economy = ____________________ %

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

Figure 1

Describe the trend shown in Figure 1.

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

Difference % yield NH₃ = ________ %

A scientist makes zinc iodide by reacting zinc with iodine. 

The equation for the reaction is: 

Zn + I₂ ⟶ ZnI₂ 

Relative atomic masses (M_r): 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

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

An equation for the reaction between copper(II) oxide and carbon is:

2CuO + C  → 2Cu + CO₂

What is the percentage atom economy for the reaction to produce copper metal?

Relative atomic masses (A_r):     C = 12        Cu = 64

Relative formula mass (M_r):       CuO = 80

Which of the following does not explain why the yield of a reaction may not be 100%?

Calcium oxide can be produced by heating calcium carbonate in a rotating kiln.

CaCO₃   →   CaO  +  CO₂

If 120 tonnes of calcium carbonate is heated in the kiln and 53 tonnes of calcium oxide are produced, what is the percentage yield?

Relative atomic masses (A_r): Ca = 40   C = 12   O= 16

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, A_r: 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

The percentage yield of copper chloride was 82.2 %. 

Calculate the mass of copper chloride produced. 

Actual mass of CuCl₂ produced = ____________ g

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 = ________________________ %

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.

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 = ____________________ %

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

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 (M_r):  N₂ = 28;  H₂ = 2;  NH₃= 17;  CH₄ = 16;  H₂O = 18

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

Give your answer in terms of equilibrium.

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

Figure 1

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.

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) 

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 (A_r):     Fe = 56,     O = 16,     C = 12

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.

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

This question is about magnesium sulfate.

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

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

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.

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

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

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

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 (A_r):     Ti = 48,     O = 16,     Mg = 24

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

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

Titanium is used for replacement hip joints.

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

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.

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

Relative atomic masses, (A_r):     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.

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.

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.

A student made zinc chloride by reacting 15.0 g of zinc carbonate with hydrochloric acid.

ZnCO₃ + 2HCl →  ZnCl₂ + CO₂ + H₂O

The percentage yield of zinc chloride was 82.4%.

Calculate the mass of zinc chloride the student actually produced.

Relative atomic masses (A_r): C = 12    Zn = 65   O= 16    Cl = 35.5     H= 1