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GCSEChemistryEdexcelExam Questions1. Atomic StructureCalculations Involving Masses

Calculations Involving Masses (Edexcel GCSE Chemistry)

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Calculations Involving Masses

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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?

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1b
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Calculate the relative formula mass iron(II) hydroxide, Fe(OH)2

(relative atomic masses: Fe = 56, O = 16, H = 1)

How did you do?

1c
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Iron(II) nitrate, Fe(NO3)2 has an Mr of 180. Calculate the percentage by mass of iron in iron(II) nitrate, Fe(NO3)2.

(relative atomic masses: Fe = 56, N = 14, O = 16)

How did you do?

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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2a1 mark

Petrol contains the fuel octane. Octane is burnt in a car engine.

The molecular formula of octane is C8H18. What is the empirical formula of octane?

  • CH2

  • C4H8

  • C4H9

  • C8H18

Choose your answer

2b2 marks

Heat from burning petrol results in other reactions taking place inside the car engine.

These reactions make molecules called nitrogen oxides.

One of the nitrogen oxides produced is nitrogen dioxide (NO2).

i) Name the elements that make up nitrogen dioxide.

[1]

ii) Give the number of atoms in a nitrogen dioxide molecule.

[1]

How did you do?

2c2 marks

Nitrogen monoxide (NO) is also produced in car engines.

Calculate the relative formula mass of nitrogen oxide.

(relative atomic masses: N = 14, O = 16)

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2d1 mark

Another molecule called nitrous oxide is made.

Each molecule contains two nitrogen molecules and one oxygen molecule.

Write the formula of nitrous oxide.

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3a1 mark

A teacher carried out a demonstration of the reaction between iron and bromine.

Figure 1 shows the equipment they used.

edx-1-6e-paper-2-q3a-iron-and-bromine-equipment

Figure 1

The teacher used a fume cupboard. Complete the sentence to explain why.

The experiment was done inside a fume cupboard because bromine is…….

How did you do?

3b1 mark

What is the name of the product formed in the reaction?

  • Bromine iron

  • Iron bromate

  • Iron bromide

  • Iron bromine

Choose your answer

3c1 mark

The mass of the iron increased during the demonstration.

Give a reason why.

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3d2 marks

The product of the reaction has the formula FeBr3.

Calculate the relative formula mass of FeBr3. (relative atomic masses: Fe = 56, Br = 80)

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4a3 marks

The rock limestone contains the compound calcium carbonate.

Calcium carbonate is a useful resource. Calcium carbonate has the formula CaCO3. Complete Figure 1 to show the number of atoms of each element in CaCO3

Element

Number of atoms in CaCO3

Calcium

 

 

1

Oxygen

 

 Figure 1

How did you do?

4b1 mark

Calcium carbonate is heated to produce calcium oxide.

The word equation for this reaction is:

 calcium carbonate → calcium oxide + carbon dioxide.

When 100 g of calcium carbonate is heated, 56 g of calcium oxide is produced.

Calculate the mass of carbon dioxide produced.

How did you do?

4c2 marks

A company needs to make 672 tonnes of calcium oxide.

Calculate the mass of calcium carbonate they will need to make this. You must show your working out.

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4d3 marks

Calcium oxide contains 71.5% calcium and 28.5% oxygen. Calculate its empirical formula.

You must show your working out.

(relative atomic masses: Ca = 40, O = 16)

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5a1 mark

A teacher demonstrated how to use the equipment in Figure 1 to calculate the empirical formula of magnesium oxide.

They made magnesium oxide by heating magnesium in air.

The reaction is:

magnesium + oxygen → magnesium oxide.

edx-1-6e-paper-2-q5a-magnesium-equipment

Figure 1

This is the method they followed:

  1. Measure the mass of the empty crucible and lid

  2. Put some magnesium ribbon into the crucible.

  3. Measure the mass of the crucible, its lid and contents.

  4. Use a Bunsen burner to heat the crucible.

  5. Keep lifting the lid a small amount to allow oxygen into the crucible.

  6. When the magnesium has stopped glowing, turn off the Bunsen burner and allow the crucible to cool down.

  7. Repeat step 3.

Give one safety rule they should follow when carrying out this experiment.

How did you do?

5b2 marks

Figure 2 shows the measurements they made.

Mass of empty crucible and lid

40.0 g

Mass of crucible, lid and contents before heating

41.2 g

Mass of crucible, lid and contents after heating

42 g

Figure 2

Use a calculation to prove:

i) The mass of magnesium used was 1.2 g.

[1]

ii) The mass of oxygen gained during heating was 0.8 g.

[1]

How did you do?

5c3 marks

Use the numbers from part b)  to calculate the empirical formula of magnesium oxide.

(relative atomic masses: Mg = 24, O = 16)

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5d1 mark

A group of students repeated the experiment.

The mass of the magnesium oxide they produced was lower than they expected.

Give one reason why.

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1
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Higher Only

How many moles are present in 9 kg of glucose, C6H12O6?

Relative formula mass (Mr):       C6H12O6 = 180

  • 0.02 mol

  • 0.05 mol

  • 20 mol

  • 50 mol

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2
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Higher Only

What is the mass of 0.25 moles of hydrated copper(II) sulfate, CuSO4.5H2O?

Relative formula mass (Mr):  H2O = 18  CuSO4 = 160

  • 40.0 g

  • 44.5 g

  • 62.5 g

  • 1000 g

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3
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Higher Only

Nitrogen and hydrogen react together to make ammonia.

N2 + 3H2  → 2NH3

If 2.0 g of hydrogen is added to 12.0 g of nitrogen which substance is the limiting reactant and how much of the excess reactant remains?

Relative atomic masses (Ar): H = 1    N = 14

 

 

Limiting Reactant

Mass of excess reactant

☐

A

nitrogen

2.0 g

☐

B

nitrogen 

10.0 g

☐

C

hydrogen

2.7 g

☐

D

hydrogen

9.3 g

    Choose your answer

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    4
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    A solution of CuSO4 has a concentration of 35 g dm-3.

    What mass of CuSO4 would there be in 250 cm3 of the solution?

    • 140 g

    • 8.75 g

    • 7.14 g

    • 1.40 g

    Choose your answer

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    5
    Sme Calculator    1 mark

    What is the relative formula mass of butene, C4H8 ?

    (relative atomic masses: H=1, C=12)

    • 12

    • 13

    • 56

    • 100

    Choose your answer

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    1a3 marks

    Iron is a metal

    Describe the structure and bonding of iron.

    How did you do?

    1b2 marks

    Higher Tier Only

    The relative atomic mass of iron is 56.

    Calculate the number of atoms in 28 g of iron.

    (Avogadro constant = 6.02 x 1023)

    How did you do?

    1c4 marks

    Higher Tier Only

    4.48 g of iron combines with 1.92 g of oxygen to form an oxide of iron.

    i) Determine the formula of this oxide of iron.

    You must show your working.

    (relative atomic masses: Fe = 56, O = 16)

    [3]

    ii) Use your answer from c) to complete the balanced equation:

    4Fe + ……..O2 → ………..

    [1]

    How did you do?

    1d4 marks

     Iron reacts with halogens to form iron(III) halides.

    The balanced equation for the reaction of iron with chlorine is:

    2Fe (s) + 3Cl2 (g) → 2FeCl3 (s)

    Calculate the mass of iron chloride formed when 14 g of iron reacts with excess chlorine.

    Give your answer to 1 decimal place.

    (relative atomic masses: Fe = 56, Cl = 35.5)

    How did you do?

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    2a1 mark

    Chemistry Only

    Figure 1 shows the structure of a molecule.

    edx-1-6h-paper-2-q2a-propanol-structure

    Figure 1

    Name the molecule.

    How did you do?

    2b1 mark

    State the empirical formula of the molecule.

    How did you do?

    2c2 marks

    Calculate the relative formula mass of the molecule.

    (relative atomic masses: C = 12, H = 1, O = 16)

    How did you do?

    2d2 marks

    Higher Tier Only

    Calculate the number of moles in 75.14 g of the molecule.

    Give your answer to 3 significant figures.

    How did you do?

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    3a3 marks

    The equipment shown in Figure 1 can be used to work out the empirical formula of magnesium oxide.

    oWsvdkuz_edx-1-6e-paper-2-q5a-magnesium-equipment

    Figure 1 

    Describe how you would use the equipment in Figure 3 to work out the mass of oxygen that will react with 6.0 g of magnesium to make magnesium oxide.

    How did you do?

    3b4 marks

    A scientist found that when 6.0 g of magnesium completely reacted the magnesium oxide formed had a mass of 10.0 g.

    Use this information to prove that the empirical formula of magnesium oxide is MgO.

    (relative atomic masses: Mg = 24, O = 16)

    How did you do?

    3c2 marks

    Higher Tier Only

    Calculate the number of moles in 9.4 g of magnesium oxide.

    Give your answer to 1 decimal place.

    How did you do?

    3d2 marks

    Higher Tier Only

    Calculate the number of atoms combined in one mole of magnesium oxide.

    (Avogadro constant = 6.02 x 1023)

    How did you do?

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    4a3 marks

    Copper sulfate solution was added to sodium hydroxide solution.

    The copper sulfate solution was prepared by dissolving 4.34 g of solid copper sulfate in water and making the volume up to 250 cm3.

    Calculate the concentration of the copper sulfate solution in g dm−3.

    Give your answer to three significant figures.

    How did you do?

    4b1 mark

    Balance the symbol equation for this reaction:

    CuSO4 (aq) + ……NaOH (aq) → Cu(OH)2 (s) + Na2SO4 (aq)

    How did you do?

    4c1 mark

    Why is this a precipitation reaction?

    How did you do?

    4d2 marks

    7.98 g of copper sulfate reacts with 4.0 g of sodium hydroxide to form 4.88 g of copper hydroxide.

    Calculate the mass of sodium sulfate made.

    How did you do?

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    5a2 marks

    A teacher demonstrates the thermite reaction, a highly exothermic reaction between aluminium and iron(III) oxide that produces molten iron.

    Explain why the iron produced is molten.

    How did you do?

    5b2 marks

    Higher Tier Only

    The symbol equation for the reaction is Fe2O3 + Al → Al2O3 + Fe

    Name the substance that is:

    i) Oxidised

    [1]

    ii) Reduced

    [1]

    How did you do?

    5c3 marks

    Higher Tier Only

    Calculate the number of moles in 8 g of iron oxide.

    (relative atomic masses: Fe = 56, O = 16)

    How did you do?

    5d3 marks

    Higher Tier Only

    The teacher used 10 g of aluminium. The relative atomic mass of aluminium is 27.

    Show that the aluminium is in excess.

    How did you do?

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