IGCSEChemistry: Co-ordinated Sciences (Double Award)CIEExam QuestionsStoichiometryThe Mole & the Avogadro Constant

The Mole & the Avogadro Constant (CIE IGCSE Chemistry: Co-ordinated Sciences (Double Award))

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1a2 marks

Ethanol is manufactured from glucose, C6H12O6, by fermentation according to the following equation.

C6H12O6 → 2C2H5OH + 2CO2

State the conditions required for this reaction.

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1b
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In an experiment, 30.0 g of glucose was fermented.

i)
Calculate the number of moles of glucose in 30.0 g.

[2]

ii)
Calculate the maximum mass of ethanol that could be obtained from 30.0 g of glucose.

[2]

iii)
Calculate the volume of carbon dioxide at room temperature and pressure that can be obtained from 30.0 g of glucose.

[1]

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1c
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Ethanol can also be manufactured from ethene.

i)
Name the raw material which is the source of ethene.

[1]

ii)
Write a balanced equation for the manufacture of ethanol from ethene.

[1]

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24 marks

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Compound X is a colourless liquid at room temperature.

A sample of pure X was slowly heated from –5.0 °C, which is below its melting point, to 90 °C, which is above its boiling point. Its temperature is measured every minute and the results are represented on the graph.

heating-curve-x

i)
Complete the equation for the equilibrium present in the region BC.

X(s) rightwards harpoon over leftwards harpoon ....................

[1]

ii)
What is the significance of temperature t°C?

[1]

iii)
What is the physical state of compound X in the region EF?

[1]

iv)
What would be the difference in the region BC if an impure sample of X had been used?

[1]

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3a1 mark

Calcium carbonate is an important raw material.

Name a rock which is made up of calcium carbonate.

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3b
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When calcium carbonate is heated strongly, it decomposes.

CaCO3 → CaO + CO2
i)
Calculate the relative formula mass of:
   CaCO3
   CaO

[2]

ii)
7.00 kg of calcium oxide was formed. What mass of calcium carbonate was heated?

[2]

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4a
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Table 1.1 shows the mass of ions present in a 100 cm3 sample of milk.

Table 1.1

ion formula of ion mass of ion in
100 cm3 milk / mg
calcium Ca2+ 125
chloride Cl− 120
magnesium Mg2+ 12
negative ions of organic acids   160
phosphate PO subscript 4 superscript 3 minus end superscript 95
potassium K+ 140
sodium Na+ 58
sulfate begin mathsize 16px style S O subscript 4 to the power of 2 minus sign end style 30

Calculate the mass of calcium ions present in a 20 cm3 sample of this milk.

mass of calcium ions: .................................... mg

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4b1 mark

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Identify the positive ion present in the highest concentration in the 100 cm3 sample of milk.

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4c1 mark

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A solution is obtained by filtering a mixture of soil and water. The table shows the mass of some of the ions in 1000 cm3 of this solution.

name of ion formula of ion mass of ion in 1000 cm3
of soil solution / mg
aluminium Al 3+ 0.2
ammonium begin mathsize 16px style N H subscript 4 to the power of plus sign end style 22.0
calcium Ca2+ 0.2
iron(II) Fe2+ 79.0
magnesium Mg2+ 0.1
nitrate NO subscript 3 superscript minus 28.0
phosphate PO subscript 4 superscript 3 minus end superscript 14.0
potassium K+ 39.0
sulfate begin mathsize 16px style S O subscript 4 to the power of 2 minus sign end style 5.1

Answer this question using the information in the table.

Which negative ion has the lowest concentration?

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4d
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A solution is obtained by filtering a mixture of soil and water. The table shows the mass of some of the ions in 1000 cm3 of this solution.

name of ion formula of ion mass of ion in 1000 cm3
of soil solution / mg
aluminium Al 3+ 0.2
ammonium begin mathsize 16px style N H subscript 4 to the power of plus sign end style 22.0
calcium Ca2+ 0.2
iron(II) Fe2+ 79.0
magnesium Mg2+ 0.1
nitrate begin mathsize 16px style N O subscript 3 to the power of minus sign end style 28.0
phosphate PO subscript 4 superscript 3 minus end superscript 14.0
potassium K+ 39.0
sulfate begin mathsize 16px style S O subscript 4 to the power of 2 minus sign end style 5.1

Answer this question using the information in the table.

Calculate the mass of nitrate ions in 200 cm3 of this solution.

mass = .............................. mg

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5
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A student completed an experiment using magnesium to displace copper from copper(II) sulfate.

Mg + CuSO4 → Cu + MgSO4

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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1a1 mark

Dilute hydrochloric acid reacts with sodium carbonate solution.

2HCl (aq) + Na2CO3 (aq) → 2NaCl (aq) + H2O (l) + CO2 (g)

Explain why effervescence is seen during the reaction.

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1b
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In another experiment, 0.020 mol of sodium carbonate were reacted with excess hydrochloric acid.

Calculate the maximum volume (at r.t.p.) of carbon dioxide gas that could be made in this reaction.

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2a4 marks

In the conical flask there is a neutral solution of potassium sulfate which still contains the indicator used in the titration.

i)
Describe how you could obtain a solution of potassium sulfate without the indicator.

[2]

ii)
Potassium hydrogen sulfate can be made by the following reaction.

KOH (aq) + H2SO4 (aq) → KHSO4 (aq) + H2O (l)

Suggest how you could make a solution of potassium hydrogen sulfate without using an indicator.

[2]

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2b2 marks

Describe a test which would distinguish between aqueous solutions of potassium sulfate and sulfuric acid.

   Test:

   Result:

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3a2 marks

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Define the following

i)
The mole

[1]

ii)
The Avogadro constant

[1]

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3b
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Which two of the following contain the same number of molecules?
Show how you arrived at your answer.

   2.0 g of methane, CH4
   8.0 g of oxygen, O2
   2.0 g of ozone, O3
   8.0 g of sulfur dioxide, SO2

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3c
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4.8 g of calcium is added to 3.6 g of water. The following reaction occurs.

Ca + 2H2O → Ca(OH)2 + H2

i)
The number of moles of Ca = ....................

The number of moles of H2O = ....................

[1]

ii)
Which reagent is in excess? Explain your choice.

[2]

iii)
Calculate the mass of the reagent named in (ii) which remained at the end of the experiment.

[1]

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4a
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A compound, Al4C3, contains only aluminium and carbon. 0.03 moles of this compound reacted with excess water to form 0.12 moles of Al(OH)3 and 0.09 moles of CH4.

Write a balanced equation for this reaction.

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4b
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0.07 moles of silicon reacts with 25 g of bromine.

Si + 2Br2 → SiBr4

i)
Which one is the limiting reagent? Explain your choice.

[3]

ii)
How many moles of SiBr4 are formed?

[1]

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5a1 mark

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Chemists use the concept of the mole to calculate the amounts of chemicals involved in a reaction.

Define mole.

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5b
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3.0 g of magnesium was added to 12.0 g of ethanoic acid.

Mg + 2CH3COOH → (CH3COO)2Mg + H2

The mass of one mole of Mg is 24 g.

The mass of one mole of CH3COOH is 60 g.

i)
Which one, magnesium or ethanoic acid, is in excess? You must show your reasoning.

[3]

ii)
How many moles of hydrogen were formed?

[1]

iii)
Calculate the volume of hydrogen formed, measured at r.t.p.

[2]

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6
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Iron(III) sulphate decomposes when heated. Calculate the mass of iron(III) oxide formed and the volume of sulphur trioxide produced when 10.0 g of iron(III) sulphate was heated. 

Mass of one mole of Fe2(SO4)3 is 400 g.

Fe2(SO4)3 (s)→ Fe2O3 (s) + 3SO3 (g)

Number of moles of Fe2(SO4)3 =

Number of moles of Fe2O3 formed = 

Mass of iron(III) oxide formed in g =

Number of moles of SO3 produced = 

Volume of sulphur trioxide at r.t.p. in dm3 =

[5]

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7
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Sulphur dioxide reacts with chlorine in an addition reaction to form sulphuryl chloride.

SO2 + Cl2 → SO2Cl2

8.0 g of sulphur dioxide was mixed with 14.2 g of chlorine. The mass of one mole of SO2Cl2 is 135 g.

Calculate the mass of sulphuryl chloride formed by this mixture.

Calculate the number of moles of SO2 in the mixture = 

Calculate the number of moles of Cl2 in the mixture = 

Which reagent was not in excess? 

How many moles of SO2Cl2 were formed =

Calculate the mass of sulphuryl chloride formed in g =

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8
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Sulfur dioxide can also be made by the reaction between a sulfite and an acid.

Na2SO3 + 2HCl → 2NaCl + SO2 + H2O

Excess hydrochloric acid was added to 3.15 g of sodium sulfite. Calculate the maximum volume, measured at r.t.p., of sulfur dioxide which could be formed.
The mass of one mole of Na2SO3 is 126 g.

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9a4 marks

Across the world, food safety agencies are investigating the presence of minute traces of the toxic hydrocarbon, benzene, in soft drinks. It is formed by the reduction of sodium benzoate by vitamin C.

bottle-of-juice

Sodium benzoate is a salt, it has the formula C6H5COONa. It can be made by the neutralisation of benzoic acid by sodium hydroxide.

i)
Deduce the formula of benzoic acid.

[1]

ii)
Write a word equation for the reaction between benzoic acid and sodium hydroxide.

[1]

iii)
Name two other compounds that would react with benzoic acid to form sodium benzoate.

[2]

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9b3 marks

The structural formula of Vitamin C is drawn below.

citric-acid

i)
What is its molecular formula?

[1]

ii)
Name the two functional groups which are circled.

[2]

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10a2 marks

The alkanes are a family of saturated hydrocarbons. Their reactions include combustion, cracking and substitution. 

i)
What is meant by the term hydrocarbon?
[1]
ii)
What is meant by the term saturated?
[1]

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10b
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The complete combustion of hydrocarbons produces carbon dioxide and water only.

i)
Write the equation for the complete combustion of nonane, C9H20.
[2]
 
ii)
20cm3 of a gaseous hydrocarbon was mixed with an excess of oxygen, 200 cm3. The mixture was ignited. After cooling, 40 cm3 of oxygen and 100 cm3 of carbon dioxide remained. Deduce the formula of the hydrocarbon and the equation for its combustion. All volumes were measured at r.t.p..
[3]

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10c4 marks

Cracking is used to obtain short-chain alkanes, alkenes and hydrogen from long-chain alkanes.

i)
Give a use for each of the three products listed above.
 
short-chain alkanes ..................................................
 
alkenes ..................................................
 
hydrogen ..................................................
[3]
 
ii)
Write an equation for the cracking of decane, C10H22, which produces two different alkenes and hydrogen as the only products.
[1]

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111 mark
In a titration, a student added 25.0 cm3 of 0.200 mol/dm3 aqueous sodium hydroxide to a conical flask. The student then added a few drops of methyl orange to the solution in the conical flask.

Dilute sulfuric acid is then added from a burette to the conical flask. The volume of dilute sulfuric acid needed to neutralise the aqueous sodium hydroxide was 20.0 cm3

The reaction is shown by the equation.

2NaOH + H2SO4 → Na2SO4 + 2H2O

State the colour of methyl orange in aqueous sodium hydroxide.

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12
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When copper(II) oxide is heated at 800 °C it undergoes the reaction shown by the equation.

4CuO → 2Cu2O + O2

Calculate the volume of oxygen, measured at r.t.p., which is formed when 1.60 g of CuO reacts as shown in the equation.

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13a1 mark

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This question is about elements X, Y and Z.

What is the name of the amount of any substance that contains 6.02 × 1023 particles?

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13b1 mark

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The constant 6.02 × 1023 has a name.

What is the name of this constant?

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14
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The equation for the reaction in stage 3 is shown.

4NO2 + 2H2O + O2 → 4HNO3

Calculate the volume of O2 gas, at room temperature and pressure (r.t.p.), needed to produce 1260 g of HNO3.


Use the following steps.

  • Calculate the number of moles of HNO3.

moles of HNO3 = ..............................

  • Deduce the number of moles of O2 that reacted.

moles of O2 = ..............................

  • Calculate the volume of O2 gas that reacts at room temperature and pressure (r.t.p.).

volume of O2 gas = .............................. dm3

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16 marks

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In the above method, a soluble salt was prepared by neutralising an acid with an insoluble base. Other salts have to be made by different methods.

i)
Give a brief description of how the soluble salt, rubidium sulphate could be made from the soluble base, rubidium hydroxide.

[3]

ii)
Suggest a method of making the insoluble salt, calcium fluoride.

[3]

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2a4 marks

Soluble salts can be made using a base and an acid.

Complete this method of preparing dry crystals of the soluble salt cobalt(II) chloride-6-water from the insoluble base cobalt(II) carbonate.

   step 1
   Add an excess of cobalt(II) carbonate to hot dilute hydrochloric acid.

  step 2

   step 3


   step 4

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2b
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i)
5.95 g of cobalt(II) carbonate were added to 40 cm3 of hydrochloric acid, concentration 2.0 mol / dm3.

Calculate the maximum yield of cobalt(II) chloride-6-water and show that the cobalt(II) carbonate was in excess.

CoCO3 + 2HCl → CoCl2 + CO2 + H2O

CoCl2 + 6H2O → CoCl2.6H2O

maximum yield:

number of moles of HCl used = .....................................................................

number of moles of CoCl2 formed = ...............................................................

number of moles of CoCl2.6H2O formed = .......................................................

mass of one mole of CoCl2.6H2O = 238 g

maximum yield of CoCl2.6H2O = ...................................................................g

to show that cobalt(II) carbonate is in excess:

number of moles of HCl used = ..................................... (use your value from above)

mass of one mole of CoCO3 = 119 g

number of moles of CoCO3 in 5.95 g of cobalt(II) carbonate = ..............................
[5]
ii)
Explain how these calculations show that cobalt(II) carbonate is in excess.
[1]

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34 marks

Crystals of sodium sulphate-10-water, Na2SO4.10H2O, are prepared by titration.

prep-sodium-sulphate-10-water

25.0 cm3 of aqueous sodium hydroxide is pipetted into a conical flask.

A few drops of an indicator are added. Using a burette, dilute sulphuric acid is slowly added until the indicator just changes colour. The volume of acid needed to neutralise the alkali is noted.

Suggest how you would continue the experiment to obtain pure, dry crystals of sodium sulphate-10-water.

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4a6 marks

Calcium and other minerals are essential for healthy teeth and bones. Tablets can be taken to provide these minerals.

Healthy Bones

Each tablet contains
calcium
magnesium
zinc
copper
boron

Boron is a non-metal with a macromolecular structure.

i)
Predict two physical properties of boron.

[2]

ii)
Name another element and a compound that have macromolecular structures.

[2]

iii)
Sketch the structure of one of the above macromolecular substances.

[2]

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4b4 marks

Describe the reactions, if any, of zinc and copper(II) ions with an excess of aqueous sodium hydroxide.

i)
Zinc ions
Addition of aqueous sodium hydroxide:
Excess sodium hydroxide:

[2]

ii)
Copper(II) ions
Addition of aqueous sodium hydroxide:
Excess sodium hydroxide:
[2]

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4c
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Extended tier only

Each tablet contains the same number of moles of CaCO3 and MgCO3. One tablet reacted with excess hydrochloric acid to produce 0.24 dm3 of carbon dioxide at r.t.p.

CaCO3 + 2HCl → CaCl2 + CO2 + H2O
MgCO3 + 2HCl → MgCl2 + CO2 + H2O

i)
Calculate how many moles of CaCO3 there are in one tablet.

Number of moles CO2 =

Number of moles of CaCO3 and MgCO3 =

Number of moles of CaCO3 =

[3]

ii)
Calculate the volume of hydrochloric acid, 1.0 mol / dm3, needed to react with one tablet.

Number of moles of CaCO3 and MgCO3 in one tablet = 
Use your answer to (c)(i).

Number of moles of HCl needed to react with one tablet =

Volume of hydrochloric acid, 1.0 mol / dm3, needed to react with one tablet =

[2]

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55 marks

The soluble salt hydrated lithium sulfate is made by titration from the soluble base lithium hydroxide.

titration-lioh--h2so4

The sulfuric acid is added slowly from the burette until the indicator just changes colour. The volume of sulfuric acid  needed to just neutralise the lithium hydroxide is noted.

Describe how you would continue the experiment to obtain pure dry crystals of hydrated lithium sulfate.

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6a1 mark

Aluminium sulfide contains two elements. Predict its formula.

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6b3 marks

Extended tier only

Draw a diagram that shows the arrangement of the outer electrons in the ionic compound sodium phosphide.

Use o to represent an electron from sodium.
Use x to represent an electron from phosphorus.

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6c
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Sodium reacts with sulphur to form sodium sulfide.

2Na + S → Na2S

An 11.5 g sample of sodium is reacted with 10 g of sulfur. All of the sodium reacted but there was an excess of sulfur.

Calculate the mass of sulfur left unreacted.

i)
Number of moles of sodium atoms reacted = 
[2 moles of Na react with 1 mole of S]

[1]

ii)
Number of moles of sulfur atoms that reacted =

[1]

iii)
Mass of sulfur reacted, in grams =

[1]

iv)
Mass of sulfur left unreacted, in grams =

[1]

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7
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Sulphur dioxide reacts with chlorine in an addition reaction to form sulphuryl chloride.

SO2 + Cl2 → SO2Cl2

8.0 g of sulphur dioxide was mixed with 14.2 g of chlorine. The mass of one mole of SO2Cl2 is 135 g.

Calculate the mass of sulphuryl chloride formed by this mixture.

Calculate the number of moles of SO2 in the mixture = ..................

Calculate the number of moles of Cl2 in the mixture = ..................

Which reagent was not in excess? ...............................

How many moles of SO2Cl2 were formed = ...................

Calculate the mass of sulphuryl chloride formed = ............. g

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