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80
YEAR-END ASSESSMENT
CHEMISTRY
PAPER 4: Theory (Extended)
Name
: ___________________________
Class
: Year 10
Day
: _____________
Date
: _____________
Duration : 1 Hour 15 Minutes
You must answer on the question paper.
No additional materials are needed.
INSTRUCTIONS
● Answer all questions.
● Use a black or dark blue pen. You may use an HB pencil for any diagrams or graphs.
● Write your answer to each question in the space provided.
● Do not use an erasable pen or correction fluid.
● You may use a calculator.
● You should show all your working and use appropriate units.
INFORMATION
● The total mark for this paper is 80.
● The number of marks for each question or part question is shown in brackets [ ].
● The Periodic Table is printed in the question paper.
_____________
Prepared by
Ms. Thevimeena
_____________
Endorsed by
Mr. S. Saravanan
2
1.
Using numbers only, state the:
(a) percentage of oxygen in clean, dry air
……………………. [1]
(b) typical operating temperature, in °C, used in the Haber process
……………………. [1]
(c) number of atoms in a diatomic molecule
……………………. [1]
(d) maximum number of electrons in the second electron shell of an atom
……………………. [1]
(e) number of hydrogen atoms in an alkaline with 7 carbon atoms
……………………. [1]
(f) number of particles in one mole, in standard form.
……………………. [1]
[Total:6]
2.
This question is about ionic compounds.
(a) State what is meant by the term ionic bond.
……………………………………………………………………………………………………
………………………………………………………………………………………………… [2]
(b) Potassium sulfide, K2S, is an ionic compound.
Complete the dot-and-cross diagram in Fig. 2.1 of the ions in potassium sulfide.
Show the charges on the ions.
Fig.2.1
[3]
3
(c) Ionic compounds form giant ionic lattices.
(i) Fig. 2.2 shows part of the giant ionic lattice structure of sodium chloride.
Complete the diagram in Fig. 2.2 to show the ions present. Use ‘+’ for sodium ions and ‘–’
for chloride ions. One chloride ion has been completed for you.
Fig. 2.2
[2]
(ii) State the name given to any positive ion.
…………………………………………………………………………………………… [1]
(d) Ionic compounds can be decomposed by the passage of an electric current using inert electrodes.
(i) State the name of this process.
………………………………………………………………………………………….... [1]
(ii)
Write the ionic half-equation for the reaction which takes place at the anode when molten
potassium bromide, KBr, is decomposed by the passage of an electric current.
…………………………………………………………………………………………... [2]
(iii) Name the products and state the observations at the negative and positive electrodes when
dilute aqueous potassium bromide, KBr, is decomposed by the passage of an electric
current.
product at the negative electrode
………………………………………………………………………………………………...
observations at the negative electrode
………………………………………………………………………………………………...
products at the positive electrode
…………………………………………… and ……………………………………………..
4
observations at the positive electrode
………………………………………………………………………………………………...
[5]
[Total:16]
5
3. Carbonyl chloride, COCl 2, is manufactured by reacting carbon monoxide with chlorine.
CO(g) + Cl2(g)
ΔH = –105 kJ / mol
COCl2(g)
The process takes place in a closed system, and an equilibrium is reached.
The conditions for this process are 200 °C and 200 kPa.
(a) Explain what is meant by the term closed system.
………………………………………………………………………………………………………... [1]
(b) State what the symbol ΔH represents.
………………………………………………………………………………………………………... [1]
(c) State how the value of ΔH shows that the forward reaction is exothermic.
………………………………………………………………………………………………………... [1]
(d) Deduce the value of ΔH for the reverse reaction. Include a sign in your answer.
………………………………………………………………………………………………………... [1]
(e) Complete Table 4.1 to show the effect, if any, on the concentration of COCl 2(g) at equilibrium when
the following changes to the conditions are applied.
Use only the words increases, decreases or no change.
Table 3.1
Change to conditions
Effect on the concentration of
COCl2(g) at equilibrium
the temperature is increased
some CO is added
the pressure is increased
a catalyst is added
[4]
6
(f) The equation for the reaction can be represented as shown in Fig. 4.1.
Fig. 3.1
Table 3.2 shows some bond energies.
Table 3.2
Use the bond energies in Table 4.2 and the value of ΔH for the reaction to calculate the bond energy,
in kJ / mol, of the C=O bond.
Use the following steps.
 Calculate the energy needed to break the bonds in the reactants.
…………………………….. kJ
 Calculate the energy released when the bonds in carbonyl chloride form.
.……………………………. kJ
 Calculate the bond energy of the C=O bond.
.……………………………. kJ/mol
[3]
7
(g) Complete the dot-and-cross diagram in Fig. 3.2 of a molecule of carbonyl chloride.
Show outer shell electrons only.
Fig. 3.2
[3]
[Total:14]
8
4. Copper(II) sulfate has the formula CuSO4. Aqueous copper(II) sulfate is a blue solution.
A sample of aqueous copper(II) sulfate is made by adding excess copper(II) oxide, CuO, to hot dilute
sulfuric acid, H2SO4.
(a) Complete the symbol equation for this reaction. Include state symbols.
CuO(..........) + H2SO4(..........) → CuSO4(..........) + ...........................(l)
[2]
(b) State one observation which shows that copper(II) oxide is added in excess.
………………………………………………………………………………………………………... [1]
(c) Describe how aqueous copper(II) sulfate can be separated from the reaction mixture.
………………………………………………………………………………………………………... [1]
(d) Crystals of hydrated copper(II) sulfate can be obtained from aqueous copper(II) sulfate by
crystallisation.
i. State what is meant by the term hydrated.
…………………………………………………………………………………………………… [1]
ii. Write the formula of hydrated copper(II) sulfate.
…………………………………………………………………………………………………… [1]
iii. Describe how this crystallisation is done.
………………………………………………………………………………………………………
………………………………………………………………………………………………………
…………………………………………………………………………………………………... [2]
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(e) Aqueous copper(II) sulfate undergoes electrolysis using graphite electrodes.
i. State why aqueous copper(II) sulfate conducts electricity.
……………………………………………………………………………………………………. [1]
ii. Give two reasons why the electrodes are made of graphite.
1 …………………………………………………………………………………………………………
2 …………………………………………………………………………………………………………
[2]
iii. Describe how the appearance of the electrolyte changes during the electrolysis of aqueous
copper(II) sulfate.
……………………………………………………………………………………………………. [1]
iv. Describe what is seen at the cathode during the electrolysis of aqueous copper(II) sulfate.
…………………………………………………………………………………………………..... [1]
v. Write the ionic half-equation for the reaction at the anode.
……………………………………………………………………………………………………. [3]
vi. State two differences seen if the electrolysis is repeated using copper electrodes instead of graphite
electrodes.
1 ………………………………………………………………………………………………………
2 ………………………………………………………………………………………………………
[2]
[Total:18]
10
5. When magnesium nitrate is heated strongly, magnesium oxide is formed.
(a) The equation for this reaction is shown.
2Mg(NO3)2 → 2MgO + 4NO2 + O2
i. State the change in oxidation number of nitrogen, N, in this reaction.
from ............................ to ............................
[2]
ii. Identify the element which is oxidised in this reaction.
……………………………………………………………………………………………………. [1]
iii. Calculate the volume of NO2 gas, at r.t.p., formed when 7.40 g of Mg(NO3)2 is heated.
Use the following steps.

Calculate the Mr of Mg(NO3)2.
………………………….

Calculate the number of moles of Mg(NO3)2 used.
…………………………. mol

Determine the number of moles of NO2 formed.
…………………………. mol

Calculate the volume of NO2 gas, in cm3, at r.t.p.
…………………………. cm3
[4]
11
(b) Magnesium oxide, MgO, is an ionic compound.
Complete the dot-and-cross diagram in Fig. 5.1 of the ions in magnesium oxide.
Give the charges on each of the ions.
Fig. 5.1
[3]
(c) Oxygen is a covalent molecule.
Complete the dot-and-cross diagram in Fig. 4.2 of a molecule of oxygen.
The inner shells have been drawn.
Fig. 5.2
[2]
[Total:12]
12
6. Silver bromide, AgBr, is made when aqueous silver ethanoate, CH3COOAg, is added to aqueous sodium
bromide, NaBr.
The equation for the reaction is shown in equation 1.
equation 1
CH3COOAg + NaBr → CH3COONa + AgBr
The method includes the following steps.
Step 1
Add 200.0 cm3 of 0.0500 mol / dm3 CH3COOAg to a beaker.
This volume contains 0.0100 mol of Ag+ ions.
Step 2
Add 50.0 cm3 of aqueous NaBr. This volume contains 0.0100 mol of Br – ions.
A precipitate forms.
Step 3
Filter the mixture.
Step 4
Dry the solid residue until all the water is removed.
Step 5
Record the mass of the dry residue.
(a) Complete the ionic equation for the reaction by adding the missing state symbols.
Ag+(.......) + Br –(.......) → AgBr(.......)
[1]
(b) Name a different aqueous silver salt which could be used in step 1.
…………………………………………………………………………………………………………… [1]
(c) Use the information in step 2 to calculate the concentration of aqueous NaBr.
concentration = .............................. mol / dm3 [1]
(d) State the colour of the precipitate which forms in step 2.
…………………………………………………………………………………………………………… [1]
13
(e) Use the information in step 1, step 2 and equation 1 to determine the number of moles of AgBr formed.
Use this value to calculate the mass of AgBr formed.
number of moles of AgBr = ..............................
mass of AgBr = .............................. g
[3]
(f) Name the salt dissolved in the filtrate in step 3.
…………………………………………………………………………………………………………… [1]
(g) The recorded mass of the dry residue in step 5 is greater than the mass calculated in (e) because a step is
missing from the procedure.
i.
Suggest the missing step.
………………………………………………………………………………………………….… [1]
ii.
Name the substance responsible for the greater mass of the dry residue.
……………………………………………………………………………………………………. [1]
(h) Barium sulfate can be made by the same method but with different aqueous solutions.
i.
Suggest two aqueous solutions which can be added together to make barium sulfate.
…………………………………………………… and ………………………………………… [2]
ii.
Write the balanced symbol equation for this reaction.
………………………………………………………………………………………………….. [2]
[Total:14]