Chemical Formulae, Equations, Calculations (Edexcel IGCSE Chemistry)

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?

[A_r of C = 12;   Zn = 65;   O = 16;  Cl = 35.5;   H = 1]

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

[M_r of  C₆H₁₂O₆ = 180 ]

The boxes show the displayed formulae of six organic compounds, P, Q, R, S, T and U.

Use the letters P, Q, R, S, T and U to answer these questions.
Each letter may be used once, more than once or not at all.

(1)

(1)

(1)

Describe a test that can be used to distinguish between compounds Q and T.

test ....................................................................................................

result with compound Q ....................................................................................................

result with compound T ....................................................................................................

Compounds P, Q and R are members of the same homologous series.

Give two characteristics of a homologous series.

This is the displayed formula of an alkene, V.

(1)

(1)

An organic compound has the percentage composition by mass

C = 36.36% H = 6.06% F = 57.58%

(2)

(2)

molecular formula = ......................................................................

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

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

Sodium hydroxide dissolves in water, forming a strongly alkaline solution.

Ammonia dissolves in water, forming a slightly less alkaline solution.

When ammonia solution reacts with sulfuric acid, a neutralisation reaction occurs and ammonium sulfate forms.

Ammonium sulfate is used by gardeners as a fertiliser because it contains nitrogen.

When zinc oxide reacts with dilute nitric acid, zinc nitrate is produced. The equation for the reaction is:

ZnO + 2HNO₃ → Zn(NO₃)₂ + H₂O

0.200 mol of nitric acid reacts with excess zinc oxide. A mass of 15.3 g of zinc nitrate is produced.
Calculate the percentage yield of zinc nitrate.
[M_r of zinc nitrate = 189]

The diagram shows the displayed formula of the organic compound methanol, CH₃OH

(1)

(1)

The atoms in methanol are held together by covalent bonds.

(2)

(2)

Another organic compound has the percentage composition by mass

(3)

empirical formula = ..............................................................

A piece of magnesium ribbon is ignited and placed in a gas jar of oxygen.

The equation for the reaction is

(1)

A second piece of magnesium ribbon is ignited and placed in a gas jar of carbon dioxide. A very exothermic reaction occurs, forming magnesium oxide and carbon.

A student uses this apparatus to find the mass of magnesium oxide that forms when a known mass of magnesium is heated.

   This is his method.

• find the mass of the crucible and lid
• place some magnesium ribbon in the crucible
• find the mass of the crucible, lid and magnesium
• heat the crucible with the lid on for a few minutes
• find the mass of the crucible, lid and magnesium oxide

Using this method, the mass of magnesium oxide formed is less than expected. Explain two changes that the student should make to his method to obtain a mass of magnesium oxide closer to the expected mass.

Halon 1301 is a compound used in some fire extinguishers.

Halon 1301 has the percentage composition by mass of 8.05% C, 53.69% Br and 38.26% F.

Calculate the empirical formula of Halon 1301.

[A_r of C = 12; Br = 80; F = 19]

Separate: Chemistry Only

What is the maximum volume, in dm³, of chlorine gas at rtp that can be obtained from 17.6 tonnes of molten potassium chloride?

[1 tonne = 10⁶ g]

[M_r of KCl = 74.5]

[Assume that the molar volume of chlorine at rtp is 24 dm³/mol]

Separate: Chemistry Only

Calculate the concentration, in mol / dm³, of a solution produced when 6.9 g of potassium carbonate, K₂CO₃, dissolves in 200 cm³ of water.

[M_r  of K₂CO₃ = 138 ]

The concentration of NaClO (aq) in a solution of bleach is found by reacting it with hydrochloric acid.

The equation for the reaction is

NaClO (aq) + 2HCl (aq) → NaCl (aq) + H₂O (l) + Cl₂ (g)

An excess of dilute hydrochloric acid is added to 4.00 cm³ of bleach solution. 60.0 cm³ of chlorine gas is produced.

Explain a safety precaution that should be taken when doing this experiment.

amount of chlorine = .............................................................. mol

amount of NaClO = .............................................................. mol

Separate: Chemistry Only

A sample of a gaseous hydrocarbon, X, has a volume of 600 cm³ at room temperature and pressure (rtp).

Calculate the amount, in moles, of hydrocarbon X in the sample.

amount of hydrocarbon X = .............................................................. mol

The mass of the sample of hydrocarbon X is 1.45g. Show that the relative molecular mass (M_r) of X is 58

M_r = ..............................................................

Hydrocarbon X is an alkane. Show that the molecular formula of X is C₄H₁₀

Give the displayed formula of the branched-chain isomer of hydrocarbon X.

The diagram shows the displayed formula of succinic acid. 

What is the empirical formula for this compound?

Many different salts can be prepared from acids.

The table shows the reactants used in two salt preparations. Complete the table to show the name of the salt formed and the other product(s) in each case.

A student uses the reaction between aluminium hydroxide and dilute sulfuric acid to prepare a pure, dry sample of aluminium sulfate crystals. The equation for the reaction used to prepare this salt is:

The diagram shows the steps in the student’s method.

The student records this information about the reagents she uses in her preparation.

Determine which reagent is in excess, making use of this information and the equation in part (b).

Another student prepares 0.025 mol of aluminium sulfate. The formula of aluminium sulfate is Al₂(SO₄)₃

Calculate the mass of aluminium sulfate prepared.

mass = .............................................................. g

The equation for another reaction used to prepare a sample of a salt is:

In one experiment, the amount of lead(II) oxide used was 0.75 mol and the amount of nitric acid used was 1.5 mol. At the end of the experiment, the mass of lead(II) nitrate obtained was 209 g.

Calculate the percentage yield of lead(II) nitrate in this experiment.

[M_r of lead(II) nitrate = 331]

Nitric acid (HNO₃) is used in the production of fertilisers.

Nitric acid is manufactured in three stages.

......................NH₃ + ......................O₂ ......................NO + .......................H₂O

(1)

Give the meaning of the symbol

(1)

(1)

Give a chemical equation for the reaction of nitrogen monoxide and oxygen in stage 2.

3NO₂ + H₂O → 2HNO₃ + NO

(4)

mass of nitric acid = ...................................................................... tonnes

(1)

When copper(II) oxide reacts with dilute nitric acid, copper(II) nitrate is produced.

The equation for the reaction is

0.200 mol of nitric acid reacts with excess copper(II) oxide.
A mass of 15.3g of copper(II) nitrate is produced.

Calculate the percentage yield of copper(II) nitrate.

[M_r of copper(II) nitrate = 187.5]

Sodium hydrogencarbonate (NaHCO₃) is also known as baking soda.

Baking soda can be used to make cakes increase in size in an oven.

This is the equation for the reaction that takes place when baking soda is heated.

2NaHCO₃ (s) → Na₂CO₃ (s) + CO₂ (g) + H₂O (g)

A student uses this apparatus to investigate the reaction that takes place when sodium hydrogencarbonate is heated.

This is the student’s method.

• Weigh a crucible and record the mass
• Add some sodium hydrogencarbonate to the crucible, reweigh it and record the mass
• Heat the crucible and contents for five minutes, then allow to cool before weighing and recording the mass
• Heat the crucible and contents again for a further three minutes, then allow to cool before weighing and recording the mass

The table shows some of the student’s results.

In a second experiment, the student uses a larger mass of sodium hydrogencarbonate. 

She calculates that she should obtain 4.8 g of sodium carbonate. 

She actually obtains 4.2 g of sodium carbonate.

This question is about alkanes.

The graph shows the boiling points of several unbranched alkanes.

(1)

(2)

boiling point = .............................................................. °C

(3)

The diagram represents two isomers with the formula C₅H₁₂

Explain why these compounds are isomers.

(2)

(1)

The equation for the complete combustion of one mole of an alkane can be represented by

Complete combustion of one mole of the alkane produces 308 g of carbon dioxide and 144 g of water.

X, Y and Z are the numbers used to balance the equation.

Calculate the values of X, Y and Z.
[M_r of CO₂ = 44, M_r of H₂O = 18]

X = ................................
Y = ................................
Z = ................................

The diagram shows the apparatus a teacher uses to determine the formula of an oxide of lead.

This is the teacher’s method.

1. Find the mass of the reduction tube
2. Add some of the lead oxide to the reduction tube
3. Find the mass of the reduction tube and lead oxide
4. Pass hydrogen gas over the lead oxide and ignite the hydrogen at the hole
5. Heat the lead oxide strongly for 10 minutes
6. Keep passing hydrogen through the reduction tube until the tube and contents are cool
7. Find the new mass of the reduction tube and its contents

The teacher completes the experiment and obtains these results.

• mass of reduction tube = 23.50 g
• mass of tube + lead oxide = 28.64 g
• mass of tube + lead = 28.16 g

The insoluble salt lead(II) chloride (PbCl₂) can be prepared by reacting a solution of lead(II) nitrate with dilute hydrochloric acid.

A student uses this apparatus to heat crystals of hydrated zinc sulfate and collect the liquid produced.

The equation for the decomposition of hydrated zinc sulfate is 

The student records these masses. 

• mass of boiling tube = 41.64 g
• mass of boiling tube + ZnSO₄·7H₂O = 54.46 g 

Calculate the maximum volume, in cm³, of pure water that could be produced.

Give your answer to 1 decimal place.

In an experiment using a different mass of ZnSO₄·7H₂O the maximum volume of pure water that could be produced is 8.5 cm³. 

The student collected the pure water and calculated the percentage yield to be 20.3%.

This question is about the reduction of metal oxides.

Solid oxides of copper can be reduced by reacting them with methane gas.
Complete the equation for the reaction between copper(II) oxide and methane.
Include state symbols.

.....CuO (.....) + .....CH₄ (.....) .....Cu (.....) + .....CO₂ (.....) + .....H₂O (.....)

A teacher uses this apparatus to demonstrate the reaction between a different oxide of copper and methane.

The teacher heats the oxide of copper until the reaction is complete.
The table shows the teacher’s results.

(4)

(1)

Iron forms when iron(III) oxide is heated with carbon.
The equation for the reaction is:

Fe₂O₃ + 3C → 2Fe + 3CO

(1)

(1)

[1 tonne = 1.0 × 10⁶ g]

(4)

mass = .............................................................. tonnes

Fe₂O₃ + 3C → 2Fe + 3CO

(2)

A student uses the reaction between zinc and dilute sulfuric acid to prepare some zinc sulfate crystals.

Zn (....................) + H₂SO₄ (....................) → ZnSO₄ (....................) + H₂ (....................)

(1)

The student adds excess zinc to a beaker of dilute sulfuric acid.

(2)

(2)

The student obtains a pure, dry sample of zinc sulfate crystals. The formula of zinc sulfate crystals is ZnSO₄.7H₂O

M_r = ..............................................................

(2)

(3)

percentage yield = ..............................................................%

Explain the meaning of the term thermal decomposition.

The equation for the thermal decomposition of potassium hydrogencarbonate is

Calculate the maximum mass of K₂CO₃ that could be produced from the thermal decomposition of 2.50 g of KHCO₃

A student is given a pure sample of sodium carbonate crystals and is told that the formula of the crystals is Na₂CO₃.xH₂O 

State what xH₂O in the formula shows about the sodium carbonate crystals.

The student uses this apparatus to find the value of x in Na₂CO₃.xH₂O

This is the student’s method.

• Find the mass of an empty crucible without a lid
• Add some sodium carbonate crystals Na₂CO₃.xH₂O to the crucible
• Find the total mass of the crucible and sodium carbonate crystals
• Heat the crucible to remove water from the crystals
• Allow the crucible and contents to cool down
• Find the mass of the cold crucible and its contents

These are the student’s results.

The student’s teacher says that the correct formula of the sodium carbonate crystals is Na₂CO₃.10H₂O

The mineral nesquehonite is a form of hydrated magnesium carbonate. The formula, MgCO₃.xH₂O, shows that nesquehonite contains water of crystallisation. When a sample of nesquohonite is heated gently, the water of crystallisation is given off and anhydrous magnesium carbonate is left. Six students are each given a sample of nesquehonite of mass 6.1 g. The students heat their samples for different times. The samples are then allowed to cool before being reweighed. The table shows their results.

Plot these results on the grid provided. The last two points have been plotted for you. Draw a straight line of best fit for the points you have plotted.

Predict the mass of sample remaining after heating for 2.5 minutes. Show on the graph how you obtain your answer.

mass after 2.5 minutes = .............................................................. g

State why the last two masses in the table are exactly the same.

A sample of nesquehonite contains 1.68 g of MgCO₃ and 1.08 g of H₂O. Calculate the value of x in the formula MgCO₃.xH₂O

x = ..............................................................

Separate: Chemistry Only

When anhydrous magnesium carbonate is heated strongly, it decomposes. The equation for the reaction is:

Calculate the volume of carbon dioxide formed in cm³, at rtp, when 4.2 g of anhydrous magnesium carbonate are completely decomposed.

[M_r of MgCO₃ = 84] [Assume that the molar volume at rtp of carbon dioxide is 24 dm³]

volume = .............................................................. cm³

Separate: Chemistry Only

A student is provided with a bottle containing a colourless solution X.

Solution X is thought to be dilute sulfuric acid of concentration 0.10 mol/dm³.

The student does some experiments on samples of solution X to try to show that it is dilute sulfuric acid.

The student adds a few drops of litmus to a sample of solution X.

The litmus turns red.

The student knows that the products of the electrolysis of dilute sulfuric acid are hydrogen and oxygen.

She carries out the electrolysis using this apparatus.

(1)

(1)

(1)

Describe a test to show that solution X contains sulfate ions.

Separate: Chemistry Only

The student then does a titration to see if the concentration of the dilute sulfuric acid is 0.10 mol/dm³.

She measures 25.0 cm³ of potassium hydroxide solution into a conical flask, and then adds a few drops of indicator solution.

(1)

(2)

amount = .............................................................. mol

H₂SO₄ + 2KOH → K₂SO₄ + 2H₂O

(3)

volume of sulfuric acid = .............................................................. cm³

Separate: Chemistry Only

This question is about three stages in the manufacture of sulfuric acid.

In stage 1, sulfur is burned in oxygen to form sulfur dioxide gas. 

(1)

(3)

maximum volume = .............................................................. dm³

Separate: Chemistry Only

In stage 2, sulfur dioxide is reacted with oxygen to form sulfur trioxide gas. 

2SO₂ (g) + O₂ (g)  2SO₃ (g)

The yield of sulfur trioxide is approximately 98%.

(2)

(1)

(1)

In stage 3, the sulfur trioxide is reacted with concentrated sulfuric acid to form a liquid called oleum, H₂S₂O₇

The oleum is then added to water to form concentrated sulfuric acid.

Complete the chemical equations for these two reactions.

............................ + ............................ → H₂S₂O₇

H₂S₂O₇ + ............................ → ...........................

Sulfuric acid reacts with ammonia to form ammonium sulfate, (NH₄)₂SO₄

Calculate the percentage by mass of nitrogen in ammonium sulfate.

percentage = .............................................................. %