AQA GCSE Chemistry: Combined Science

Topic Questions

3.1 Measurement, Mass & Equations

1a1 mark

This question is about reactions of iron.

Iron can form iron (III) oxide with a chemical formula of Fe2O3.

How many atoms are shown in the formula Fe2O3?

1b1 mark

How many atoms are shown in the formula for iron (II) hydroxide, Fe(OH)2?

1c1 mark

How many atoms are present in iron (II) nitrate, Fe(NO3)2?

1d3 marks

Recent discoveries in the fields of Geology and Seismology have established the potential existence of a previously undiscovered iron oxide compound, FeO2.

This iron oxide requires very high pressures and temperatures to form.

In theory, FeO2 could be formed by the reaction of iron and oxygen, under suitable conditions, as follows.

Fe + O2 → FeO2

How does this reaction demonstrate the law of conservation of mass?

Draw a ring around the correct answers to complete the sentences.

There is/are 

one

two

three

 atom(s) of iron on both sides of the equation 
 
There is/are 

one

two

three

 atom(s) of oxygen on both sides of the equation 
 
The total number of atoms 

increases

stays the same

decrease

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2a2 marks

This question is about reactions involving calcium compounds.

Heating calcium carbonate, CaCO3, produces calcium oxide, CaO, and one other gaseous product.

Write the word equation for this reaction.

2b1 mark

Write a balanced chemical equation for heating calcium carbonate, CaCO3, to form calcium oxide, CaO, and one other gaseous product.

2c
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1 mark

Calcium hydroxide, Ca(OH)2 can be made by the reaction of calcium oxide, CaO, with water.

CaO + H2O → Ca(OH)2 

112 g of calcium oxide reacts with 36 g of water.

Calculate the mass of calcium hydroxide that is produced.

____________________ g

2d
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1 mark

What mass of calcium oxide would react with 36 tonnes of water to form calcium hydroxide?

___________________ tonnes

2e
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2 marks

Calcium hydroxide can be used to test for the presence of carbon dioxide.

If carbon dioxide is present, the calcium hydroxide will form a milky white precipitate of calcium carbonate.

The formula of calcium carbonate is CaCO3.

Calculate the relative formula mass (Mr) of calcium carbonate.

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

2f
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2 marks

Calculate the percentage of oxygen in calcium carbonate, CaCO3, using the following equation.

Percentage by mass = fraction numerator A subscript straight r cross times space number space of space atoms over denominator M subscript straight r space of space the space compound end fraction space cross times space 100

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3a1 mark

A student investigated the reaction between copper carbonate and dilute hydrochloric acid.

The equation for the reaction is:

CuCO3 (s) + 2HCl (aq) ⟶ CuCl2 (aq) + CO2 (g) + H2O (l)

What state of matter is carbon dioxide in?

Tick (one box.

Aqueous  
Gas  
Liquid  
Solid   
3b1 mark

This is the method that the student used to complete their investigation.

  1. Pour 100 cm3 of dilute hydrochloric acid into a conical flask.
  2. Place the conical flask on a 2 decimal place balance.
  3. Add 2.00 g of copper carbonate lumps to the conical flask.
  4. Wait until the copper carbonate stops reacting.
  5. Record the decrease in mass of the conical flask and contents.
  6. Repeat steps 1 to 5 two more times.

Table 1 shows the student’s results.

Table 1

  Trial 1 Trial 2 Trial 3 Mean
Decrease in mass of the conical flask and contents in grams 0.74 0.69 0.76 X


Why do the contents of the conical flask lose mass during the investigation?

3c
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1 mark

Calculate the value for the mean mass X in Table 1.

3d1 mark

How would the student know that a reaction was taking place?

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4a1 mark

A student investigated the rate of reaction between calcium carbonate and hydrochloric acid.

CaCO3 (s) + HCl (aq) → CaCl2 (aq) + CO2 (g) + H2O (l)

The apparatus that the student used is shown in Figure 1.

Figure 1

aqa-gcse-3-1e-4a-mass-loss-caco3-hcl-reaction

What type of reaction occurs between calcium carbonate and hydrochloric acid?

Tick (one box.

Combustion  
Decomposition  
Endothermic  
Neutralisation   
4b3 marks

Table 1 shows the student’s results for one investigation.

Table 1

Time in s

0 30 60 90 120 150 180

Mass lost in g

0.0 1.7 2.6 3.7 3.4 4.1 4.1

  • Plot these results on Figure 2.
  • Draw a line of best fit.

Figure 2

-~0xPunB_aqa-gcse-3-1e-q4b-blank-graph

4c2 marks

Use Figure 2 to complete Table 2.

Table 2 

Mass lost after 45 seconds

______ g

Time taken to lose 1.0 g 

______ s

4d2 marks

Use Table 1 to determine the resolution and uncertainty of the balance that the student used for their experiment.

Resolution = __________ g

Uncertainty = ± __________ g

4e
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2 marks

Another student repeats the same experiment three times. 

The loss in mass that the student measured at 60 seconds was

2.9 g      2.7 g      2.8 g

Estimate the uncertainty in the loss of mass readings at 60 seconds.

Show how you determine your estimate.

Uncertainty = ± __________ g

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1a3 marks

This question is about titanium.

Titanium is a transition metal that is extracted from titanium dioxide in a two-stage industrial process.

In the first stage, titanium dioxide reacts with carbon and chlorine to form titanium tetrachloride and carbon monoxide.

Write the balanced symbol equation for this reaction.

1b1 mark

Explain how your chemical symbol equation in part (a) demonstrates the law of conservation of mass.

1c2 marks

Identify two hazards associated with Stage 1.

1d
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2 marks

Calculate, to three significant figures, the percentage by mass of chlorine in titanium tetrachloride.

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2a1 mark

Magnesium displaces copper from copper sulfate solution.

Write the word equation for the reaction.

2b2 marks

State two changes that would be observed during the displacement reaction.

2c2 marks

Write the ionic equation for the displacement of copper from copper sulfate by magnesium. You should include state symbols.

2d2 marks

Displacement reactions are examples of redox reactions.

Explain why the displacement reaction between magnesium and copper sulfate is both reduction and oxidation.

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3a2 marks

This question is about lead nitrate.

Lead nitrate is an ionic compound with the chemical formula Pb(NO3)2.

State the number of each atom and the total number of atoms present in the formula of lead nitrate.

3b
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2 marks

Calculate the percentage by mass of oxygen in lead nitrate, Pb(NO3)2.

3c3 marks

A displacement reaction occurs between solutions of lead nitrate and potassium iodide, KI, to form solid lead (II) iodide and aqueous potassium nitrate.

Write the balanced symbol equation, including state symbols, for this reaction.

3d2 marks

Table 1 summarises the solubility of a selection of ionic compounds in water.

Table 1

Soluble Insoluble
All nitrates  
Most common chlorides Silver chloride, lead chloride
Most common sulfates Lead sulfate, barium sulfate, calcium sulfate
Sodium carbonate, potassium carbonate, ammonium carbonate Most common carbonates


The displacement reaction between lead nitrate and potassium iodide forms a yellow precipitate.

Justify which chemical is responsible for the yellow colour.

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4a2 marks

A student completes two experiments in the school laboratory.

In the first experiment, the student measures a known mass of green copper carbonate powder, CuCO3, into a crucible and heats it strongly for around 5 minutes.

After the crucible has cooled, the student measures the mass of the powder that remains.

The student incorrectly concludes that there must be an error in the experiment because the mass of powder has decreased.

Explain why the mass of powder should decrease. Your answer should include a balanced chemical equation with state symbols.

4b1 mark

In terms of electrons, explain why the thermal decomposition of copper carbonate is not a reduction or oxidation reaction.

4c2 marks

In the second experiment, the student places 5 cm3 of hydrochloric acid into a test tube.

The test tube is then stood inside a beaker which is placed on top of a one decimal place balance.

The student cuts a 2 cm piece of magnesium ribbon, places it into the acid and resets the balance immediately.

The student is satisfied that a reaction is occurring because they see bubbles of gas, however, the balance shows no significant change in mass.

Suggest why there might be no significant change in mass. Justify your answer with a balanced symbol equation.

4d2 marks

The student suggests that the second experiment between magnesium and hydrochloric acid could be improved by using a gas syringe to collect continuous data.

Suggest a piece of equipment that could be used to collect an alternative set of continuous data for this reaction. Justify your answer. 

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5a2 marks

This question is about the decomposition of hydrogen peroxide.

Hydrogen peroxide solution, H2O2, decomposes slowly at room temperature to form a liquid and a gas.

The gas formed will relight a glowing splint.

Write a balanced chemical equation, including state symbols, for the decomposition of hydrogen peroxide.

5b
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3 marks

A student investigates the volume of gas produced by the decomposition of hydrogen peroxide using a manganese dioxide catalyst.

The student's results are shown in Table 1.

Table 1

  Volume of gas produced in cm3
Time in s Experiment 1 Experiment 2 Experiment 3 Average
10 58.0 56.0 54.0 56.0
20 79.0   80.0 80.3
30   93.5   91.5 ± 2.0
40 99.0 100.0 80.0  
50 100.0 100.0 100.0 100.0
60 100.0 100.0 100.0 100.0


Calculate the missing values for the results at 20 s and 40 s.

5c
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2 marks

Use Table 1 to calculate the missing results for 30 s.

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1a1 mark

A student set up an experiment to investigate the law of conservation of mass.

The law states that in a chemical reaction, the mass of the products is equal to the mass of the reactants.

This is the method that the student followed.

    1. Prepare a beaker of lead nitrate solution and label it A.
    2. Prepare a beaker of potassium chromate solution and label it B.
    3. Measure the mass of both beakers and contents with an accurate and tared balance.
    4. Pour the solution from beaker B into beaker A.
    5. Immediately measure the mass of both beakers and contents.

This is the equation for the reaction which occurs when the solutions are mixed together: 

Pb(NO3)2 (aq) + K2CrO4 (aq) ⟶ PbCrO4 (s) + 2KNO3 (aq)

What would the student observe as the reaction takes place?

1b3 marks

The student’s results are shown in Table 1.

  Table 1

 

Mass in g

Beaker A and contents before mixing

127.60

Beaker B and contents before mixing

126.86

Beaker A and contents after mixing

153.09

Beaker B after mixing

101.37

Use the data from the table to show that the law of conservation of mass is true.

1c1 mark

What is the resolution of the balance used in the experiment?

Tick (✔) one box.

0.1 g   0.01 g   1.0 g   10.0 g  
1d2 marks

Calculate the relative formula mass (Mr) of the compound lead nitrate Pb(NO3)2 

Relative atomic masses (Ar): N = 14; O = 16; Pb = 207

Relative formula mass = ____________________

1e3 marks
A fellow student also tests the law of conservation of mass and decides to use the same method but performs the experiment with a different reaction.
 

The equation for the reaction is: 

Na2CO3 (aq) + 2HCI (aq) ⟶ 2NaCl (aq) + CO2 (g) + H2O (I)

This student's results appear to fail to support the law of conservation of mass.

Explain why this is so.

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2a1 mark

A student investigated the rate of reaction using marble chips and hydrochloric acid.

The apparatus used in the experiment is shown in Figure 1.

Figure 1

3-1-measurement-mass--equations-medium-q2a-copy

What is the object labelled A?

Tick (✔) one box.   

limestone

 

cotton wool

 

rockwool

 

rubber bung

 
2b3 marks

Table 1 shows the results obtained for one investigation.

Table 1

Time in s

Mass lost in g

0

0.0

20

0.8

40

2.5

60

2.8

80

3.6

100

4.0

120

4.0

Plot these results on Figure 2 and draw a line of best fit. 

Figure 2

3-1-measurement-mass--equations-medium-q2b-copy

2c2 marks

Use Figure 2 to complete Table 2.

Table 2

Amount of mass lost after 0.5 minutes

______ g

Time taken for reaction to go to completion

______ s

2d2 marks

The balanced chemical equation for the reaction is:

 2HCl (aq) + CaCO3 (s) → CaCl2 (aq) + H2O (l) + CO2 (g)

Explain why this investigation produced a loss in mass.

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3a5 marks

Balance the following chemical equations:

i)
Fe + Cl2 → FeCl3 
[1 mark]
ii)
Fe + O2 → Fe2O3 
[1 mark]
iii)
FeBr3 + H2SO4 → Fe2(SO4)3 + HBr
[1 mark]
iv)
KNO3 + H2CO3 → K2CO3 + HNO3
 [1 mark]
v)
C5H12 + O2 → CO2 + H2O       
[1 mark]
3b3 marks

Explain why an unbalanced chemical equation cannot correctly describe a chemical reaction.

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4a2 marks

The molecular formula of iron sulfate is Fe2SO4.

Calculate the relative formula mass of Fe2SO4.

Relative atomic masses: Fe = 56; O = 16; S = 32

Answer = ________________________

4b2 marks

Calculate the percentage by mass of sulfur in Fe2SO4.

Percentage of sulfur = _____________%

4c2 marks

Iron oxide (Fe2O3) is the main compound in iron ore when it is extracted. 

Calculate the relative formula mass of Fe2O3 

Relative atomic masses: O = 16; Fe = 56.

Answer = ________________________

4d2 marks

Calculate the percentage by mass of iron in Fe2O3.

You may need to use part of your answer from 4(c).

Percentage of iron = _____________________ %

4e1 mark

What is the mass of iron that could be extracted from 500 kg of iron oxide?

You may need to use part of your answer from 4(d).

Mass of iron = __________________________ kg

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5a1 mark

A chemist was asked to analyse a nitrogen compound. She used a mass spectrometer to find the relative formula mass (Mr) of the compound. 

Its value was found to be 44. 

Relative atomic masses: N = 14, O = 16 

Draw a ring around the correct formula of the compound. 

NO2                 N2O                  N2O3                 N2O4

5b2 marks

Some students investigated magnesium oxide which has the formula MgO. 

Calculate the relative formula mass (Mr) of MgO. 

Relative atomic masses: O = 16; Mg = 24.

Relative formula mass = ___________________

5c2 marks

What is the percentage by mass of magnesium in MgO?

Percentage by mass of Mg in MgO = _______%

5d3 marks

The students calculated that 0.15 g of magnesium should give them 0.24 g of magnesium oxide. 

They performed the following experiment as illustrated in Figure 1 to find out if this was correct.

Figure 1
3-1-measurement-mass--equations-medium-q5d
  • The students weighed out 0.15 g of magnesium ribbon and placed it in a crucible.
  • They heated the crucible over a bunsen burner.
  • They lifted the lid of the crucible occasionally to allow air into the crucible but not too much in case some of the magnesium oxide escaped.
  • When all of the magnesium appeared to have reacted, the students weighed the magnesium oxide produced.

The results of the experiment are shown in Table 1:

   Table 1

Mass of magnesium used (g)

0.15

Mass of magnesium oxide produced (g)

0.21

 

The final mass of MgO produced was less than expected which they thought was due to experimental error. 

Suggest three experimental errors that the students had made.

5e2 marks

The students performed the experiment only once. 

Give two reasons why they should have repeated the experiment.

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