Topic questions Quantitative chemistry Empirical formulae
13 questions · 159 marks · about 3.5 hours
11.895 g of hydrated cobalt(II) chloride, CoCl2•xH2O, is heated to remove the water of crystallisation.
After heating to constant mass, the mass of the anhydrous salt was 6.495 g.
What is the value of x ?
A 3
B 5
C 6
D 7
This question is about reactions of compounds of iron and copper.
Complete the electron configuration of
an Fe atom: 1s2........
a Cu2+ ion: 1s2........
Solutions of iron(II) sulfate, FeSO4, and copper(II) sulfate, CuSO4, can be distinguished by adding aqueous sodium hydroxide.
Describe what would be observed when NaOH(aq) is added to each solution.
Observation with FeSO4(aq)........
Observation with CuSO4(aq)........
The cyclic organic compound pyridine, C5H5N, can act as a monodentate ligand.
The structure of pyridine is shown below.
What is meant by a monodentate ligand ?
Aqueous copper(II) sulfate reacts with salicylic acid to form a complex ion which has two stereoisomers.
One isomer of the complex ion is shown:
Draw the other stereoisomer of the complex.
Identify the type of stereoisomerism shown by the complexes.
Type of stereoisomerism........
Calculate the percentage by mass of CuSO4•5H2O in Mixture A.
Give your answer to 3 significant figures.
Percentage of CuSO4•5H2O in Mixture A =........ %
The student repeats their method, but after carrying out Step 1 they leave the solution exposed to the air for a few days. Some of the iron(II) sulfate is oxidised to iron(III) sulfate.
The student then continues with Step 2, Step 3 and Step 4 of the method.
This mean titre is greater than 31.15 cm3.
Suggest why this mean titre is greater than 31.15 cm3.
Also involves Chemical measurements and uncertainty
This question is about compounds and ions of iron(II) and iron(III) that contain ethanedioate ions, C2O42–.
The C2O42– ion, shown below, is an example of a bidentate ligand.
Explain what is meant by the term bidentate ligand.
A complex ion E contains three C2O42– ions bonded to an iron(III) ion in an octahedral shape.
Complex ion E exists as a mixture of two optical isomers.
Draw 3D diagrams to show the structures of the optical isomers of E.
Include any overall charge.
A student plans an investigation to find the number of waters of crystallisation, x, in a sample of hydrated iron(II) ethanedioate, FeC2O4•xH2O.
The student decides to carry out a redox titration between solutions of iron(II) ethanedioate and potassium manganate(VII) in acidic conditions.
In the titration, both iron(II) ions and ethanedioate, C2O42–, ions are oxidised.
Construct half-equations for the oxidation of iron(II) and ethanedioate ions.
Oxidation of iron(II) ions
Oxidation of ethanedioate ions
The uncertainty in each burette reading is ±0.05 cm3.
Calculate the percentage uncertainty for the titre in Titration 1.
* In the titration, 5 mol of iron(II) ethanedioate reacts with 3 mol of manganate(VII) ions.
Analyse the student’s results to find the number of waters of crystallisation, x, in the hydrated
iron(II) ethanedioate, FeC2O4•xH2O.
0.688 g of an oxide of manganese is reduced by hydrogen gas to form manganese metal and 0.235 g of water.
What is the formula of the oxide of manganese?
A MnO
B MnO2
C Mn2O3
D Mn3O4
Your answer
Also involves Tests for gases
Tutton’s salts are ‘double salts’ with the formula X2Y(ZO4)2 • 6H2O.
A Tutton’s salt contains two cations: X+ and Y2+.
• X + can be an ion of the Group 1 elements K, Rb, Cs or Fr, or an ammonium ion.
• Y2+ can be a 2+ ion of magnesium or an ion of most of the transition elements in Period 4.
• Z can be S or Cr.
(NH4)2Cu(SO4)2 • 6H2O is an example of a Tutton’s salt.
Predict the formula of a Tutton’s salt containing different ions from (NH4)2Cu(SO4)2 • 6H2O.
A student prepares a sample of the Tutton’s salt, (NH4)2Cu(SO4)2 • 6H2O using the method shown below.
Step 1 Dissolve 0.025 mol of ammonium sulfate and 0.025 mol of hydrated copper(II) sulfate, CuSO4 • 5H2O, in water and make up to 50 cm3.
Step 2 Boil the resulting mixture for 2 minutes and allow to cool.
Step 3 Allow the solvent to evaporate slowly. Pale blue crystals of the Tutton’s salt form.
What masses are needed of ammonium sulfate and CuSO4 • 5H2O?
mass of ammonium sulfate........ g
mass of CuSO4 • 5H2O........ g
In Step 3, why does the student allow the solvent to evaporate and not boil off all the solvent in Step 2 ?
The student dissolves their Tutton’s salt in water. A pale blue solution forms.
The student carries out two tests on this aqueous solution.
The student adds an excess of aqueous ammonia to their aqueous solution of Tutton’s salt. A deep blue solution forms.
The complex ion responsible for the deep blue solution has a molar mass of 167.5 g mol–1.
Suggest the formula of this complex ion.
The student adds NaOH(aq) to the aqueous solution of Tutton’s salt and warms the mixture.
A precipitate and a gas are formed.
Write the formulae of the precipitate and gas and suggest a test that could confirm the identity of the gas.
Formula of precipitate........
Formula of gas........
Test to confirm the identity of the gas........
How could the student carry out a test-tube test to confirm the anion in the Tutton’s salt?
This question is about nitric acid, hydrochloric acid and sulfuric acid.
Dilute nitric acid reacts with aluminium oxide to form a solution of aluminium nitrate.
Write an equation for this reaction.
The solution contains nitrate ions, NO3–.
Draw a ‘dot-and-cross’ diagram for the NO3– ion.
Use a different symbol for the extra electron.
Balance the half-equation for the oxidation process in this reaction.
In the reduction process in this reaction, HNO3 and H+ react together to form 2 oxides: X (Mr = 30) and Z (Mr = 18).
Determine the formulae of X and Z and write the half-equation for this reduction.
* Three reactions involving sulfuric acid are shown below.
Reaction 1 Dilute sulfuric acid is reacted with nickel(II) hydroxide to form a green solution.
The solvent is allowed to evaporate leaving hydrated crystals of compound D, with the percentage composition by mass: Ni, 22.33%; S, 12.20%; O, 60.87%; H, 4.60%.
Reaction 2 Concentrated sulfuric acid is reacted with hydrogen bromide, HBr, to form three products:
• an element which exists as diatomic molecules
• a gaseous compound E
• a liquid.
At RTP, 1.00 dm3 of compound E has a mass of 2.67 g.
Reaction 3 Concentrated sulfuric acid acts as a catalyst when 2-hydroxypropanoic acid reacts to form compound F (Mr = 144).
In this reaction, 2 mol of 2-hydroxypropanoic acid forms 1 mol of compound F and 2 mol of water.
Identify compounds D, E and F and construct equations for the reactions.
Show structures for any organic compounds.
This question is about d-block elements.
Most d-block elements are also classified as transition elements.
Explain why scandium and zinc are classified as d-block elements but are not also transition elements.
Your explanations should include full electron configurations.
What is meant by a bidentate ligand ?
* Determine the formulae of A and B. Write the ionic equation for the ligand substitution and show 3D structures for the three stereoisomers of B.
Complete combustion of 1.00 g of a hydrocarbon gives 3.38 g carbon dioxide.
What is the empirical formula of the hydrocarbon?
A CH
B CH2
C C2H5
D C3H8
Also involves Hazard symbols and risk assessment
This question is about elements and compounds in Group 14 (Group 4) of the periodic table.
There are four oxides of lead: PbO, PbO2, Pb2O3 and Pb3O4.
A student carries out an experiment to identify an unknown lead oxide, which is one of the four oxides of lead shown above.
The student plans to reduce the unknown lead oxide to lead by heating the lead oxide in a stream of methane gas, CH4. The apparatus is shown below.
Student’s method
• Weigh an empty dish. Add the lead oxide to the dish and reweigh.
• Set up the apparatus and pass methane gas through the tube as shown. Heat the dish for 10 minutes.
• Pass cold air through the tube to cool the dish and contents.
• Weigh the dish and contents.
Write the equation for the reduction of Pb2O3 with CH4.
The student uses safety glasses and a lab coat.
State, with a reason, one other important safety precaution the student should take when carrying out this experiment.
The student was not sure that all the oxygen had been removed from the lead oxide.
Suggest two modifications that the student could make to their method to be confident that all the oxygen had been removed. Explain your reasoning.
The student makes suitable modifications to the method and repeats the experiment to obtain the accurate results shown below.
Calculate the empirical formula of the lead oxide.
SiO2 and CO2 are oxides of other Group 14 (Group 4) elements.
Solid SiO2 melts at 2156 °C. Solid CO2 melts at −56 °C.
Suggest the type of lattice structure in solid SiO2 and in solid CO2 and explain the difference in melting points in terms of the types of force within each lattice structure.
Structure in SiO2(s)........
Structure in CO2(s)........
Explanation........
Also involves Thermal decomposition
This question is about reactions of iron compounds.
In the boxes, write the formulae of A and B.
The student thinks that the reaction of iron(II) sulfide with H+ / H2O is a redox reaction.
Explain, with reasons, whether the student is correct.
Write the equation for the reaction of [Fe(H2O)6]2+(aq) with Cl2(g).
Construct an equation for the reaction of H2S(g) with H+(aq)/MnO4−(aq).
Also involves Chemical measurements and uncertainty
This question is about the halogen group of elements and some of their compounds.
The halogens show trends in their properties down the group.
The boiling points of three halogens are shown below.
| Halogen | Boiling point / °C |
| Chlorine | –35 |
| Bromine | 59 |
| Iodine | 184 |
Explain why the halogens show this trend in boiling points.
Hydrogen iodide, H I, is decomposed by heat into its elements:
The decomposition is much faster in the presence of a platinum catalyst.
Complete the enthalpy profile diagram for this reaction using formulae for the reactants and products.
• Use Ea to label the activation energy without a catalyst.
• Use Ec to label the activation energy with a catalyst.
• Use 
H to label the enthalpy change of reaction.
Compound A is an oxide of chlorine that is a liquid at room temperature and pressure and has a boiling point of 83 °C.
When 0.4485 g of A is heated to 100 °C at 1.00 × 105 Pa, 76.0 cm3 of gas is produced.
Determine the molecular formula of compound A.
Show all your working.
Complete Table 20.1 and calculate the mean titre that the student should use for analysing the results.
The uncertainty in each burette reading is ±0.05 cm3.
Calculate the percentage uncertainty in the titre obtained from titration 1.
Give your answer to two decimal places.
Describe and explain how the student should determine the end point of this titration accurately.
Determine the relative formula mass and formula of the Group 1 iodate(V), B.
Show your working.
This question is about some reactions of d block elements and their ions.
Table 21.1 shows standard electrode potentials which will be needed within this question.
Complete the electron configuration of
a Ni atom: 1s2........
a Ni2+ ion: 1s2........
A standard cell is set up in the laboratory with the cell reaction shown below.
Draw a labelled diagram to show how this cell could be set up to measure its standard cell potential.
Include details of apparatus, solutions and the standard conditions required.
Standard conditions........
Predict the standard cell potential of this cell.
Use the information in Table 21.1 to help you answer both parts of this question.
Write the overall equation for the oxidation of Fe2+ by acidified H2O2.
Zinc reacts with acidified Cr2O72– ions to form Cr2+ ions in two stages.
Explain why this happens in terms of electrode potentials and equilibria.
Include overall equations for the reactions which occur.
* Three different reactions of copper compounds are described below.
Reaction 1: Aqueous copper(II) sulfate reacts with excess aqueous ammonia in a ligand substitution reaction. A deep-blue solution is formed, containing an octahedral complex ion, C, which is a trans isomer.
Reaction 2: Copper(I) oxide reacts with hot dilute sulfuric acid in a disproportionation reaction. A blue solution, D, and a brown solid, E are formed.
Reaction 3: Copper(II) oxide reacts with warm dilute nitric acid in a neutralisation reaction, to form a blue solution. Unreacted copper(II) oxide is filtered off, and the solution is left overnight in an evaporating basin. A hydrated salt, F, crystallises, with the percentage composition by mass: Cu, 26.29%; H, 2.48%; N, 11.59%; O, 59.63%.
Identify C – F by formulae or structures, as appropriate.
Include equations, any changes in oxidation number, and working.
The relative molecular masses and boiling points of some fuels are shown in Table 22.1.
Write an equation for the incomplete combustion of heptane.
Explain the difference in the boiling points of the fuels in Table 22.1.
Fuel additives are often used to improve the combustion of a fuel.
Compound N is a fuel additive containing carbon, hydrogen and oxygen only.
Complete combustion of 1.71 g of compound N produces 2.97 g of CO2 and 1.62 g of H2O. The relative molecular mass of compound N is 76.0.
Calculate the molecular formula of N and suggest a possible structure for the compound.
compound N
Solketal has been investigated as a potential fuel additive.
Solketal is synthesised from propane-1,2,3-triol and a carbonyl compound.
Construct a balanced equation for this synthesis. Show structures for the organic compounds in your equation.
* A scientist is researching compounds that might be suitable as fuel additives. One of the compounds gives the analytical results below.
Elemental analysis by mass: C: 54.54%; H: 9.10%; O: 36.36%
Mass spectrum: Molecular ion peak at m / z = 132.0
1H NMR spectrum in D2O
The numbers by the peaks are the relative peak areas.
When the spectrum is run without D2O, there are two additional peaks with the same relative peak areas at 11.0 ppm and 3.6 ppm.
Use the information provided to suggest a structure for the compound.
Show all your reasoning.
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