Question
This question is about chemical reactions and electricity.
(a) The diagram shows the apparatus used in the production of electrical energy in a simple cell.
The zinc electrode dissolves in the electrolyte forming Zn2+(aq) ions.
(i) Draw an arrow on the diagram to show the direction of electron flow. [1]
(ii) Write the ionic half-equation for the reaction that occurs when the zinc electrode dissolves.[2]
(b) The reading on the voltmeter can be increased if either zinc or iron is replaced by another metal.
(i) Name a metal that can replace zinc and increase the reading on the voltmeter.[1]
(ii) Name a metal that can replace iron and increase the reading on the voltmeter.[1]
(c) Fuel cells are used to generate electricity.
(i) Name the reactants in a fuel cell.[1]
(ii) Name the waste product of a fuel cell.[1]
(d) Electricity can be used to break down aqueous or molten ionic compounds.
(i) Name the process which uses electricity to break down aqueous or molten ionic compounds.[1]
(ii) Explain why the ionic compound needs to be aqueous or molten.[1]
(e) Brine is concentrated aqueous sodium chloride.
(i) Name three substances which are manufactured by passing electricity through brine. [3]
1
2
3
(ii) Name a different substance formed when molten sodium chloride is used instead of concentrated aqueous sodium chloride.[1] [Total: 13]
Answer/Explanation
Ans:
4(a)(i) arrow going from Zn to Fe
4(a)(ii) Zn → Zn2+ + 2e–
Zn as only reactant and Zn2+ as only product
correct equation
4(b)(i) any metal above zinc in reactivity series
4(b)(ii) any metal below iron in reactivity series
4(c)(i) hydrogen and oxygen
4(c)(ii) water
4(d)(i) electrolysis
4(d)(ii) mobile ions
4(e)(i) hydrogen
chlorine
sodium hydroxide
4(e)(ii) sodium
Question
Petroleum is a useful natural resource.
The diagram shows how petroleum can be separated into useful substances.
(a) What is the name of the separation process shown in the diagram?
(b) Name the fraction leaving at:
A ………………………………………………………………………………………………………………………………
B ………………………………………………………………………………………………………………………………
(c) Refinery gas is a mixture of hydrocarbons.
One refinery gas is butane, \(C_4H_{10}\).
(i) Suggest the names of two other refinery gases.
……………………………………………………… and ……………………………………………………..
(ii) Write the chemical equation for the complete combustion of butane.
(iii) Name the toxic gas produced by the incomplete combustion of butane.
(d) Gasoline and kerosene are both fuels. They have different properties.
(i) Describe the differences in the properties given.
viscosity of the fuel ……………………………………………………………………………………………….
flammability of the fuel …………………………………………………………………………………………..
(ii) What difference in the molecules of gasoline and kerosene causes these differences in
properties?
(e) Hydrogen fuel cells can be used to power vehicles.
Write the word equation for the overall reaction that takes place in a hydrogen fuel cell.
Answer/Explanation
Answer:
(a) distillation (1)
fractional (1)
(b) naphtha (1)
bitumen (1)
(c) (i) any two from:
methane ethane propane
(ii) \(2C_4H_{10} + 13O_2 \rightarrow 8CO_2 + 10H_2O\)
\(CO_2\) and \(H_2O\) as products (1) correct equation (1)
(iii) carbon monoxide
(d) (i) kerosene is more viscous
gasoline is more flammable
(ii) kerosene has molecules with a longer carbon chain
(e) hydrogen + oxygen \(\rightarrow \) water
Question
Limestone rock is mainly calcium carbonate, CaCO3.
(a) The ‘limestone cycle’ is shown. Each step is numbered.
(i) Complete the box to give the chemical name and formula of lime. [2]
(ii) Which step involves a physical change?[1]
(iii) What type of reaction is step 1?[1]
(iv) Suggest how step 2 could be reversed.[1]
(v) Write a chemical equation for step 4.[1]
(vi) Explain why step 4 is a neutralization reaction. Refer to the substances reacting in your answer.[2]
(b) Dolomite is a similar rock to limestone. Dolomite contains magnesium carbonate, MgCO3. Write a chemical equation for the reaction between magnesium carbonate and dilute nitric acid.[2]
(c) Forsterite is another rock which contains a magnesium compound.
A sample of forsterite has the following composition by mass: Mg, 2.73g; Si, 1.58g; O, 3.60g.
Calculate the empirical formula of forsterite.
empirical formula = [2] [Total: 12]
Answer/Explanation
Ans:
3(a)(i) M1 calcium oxide
M2 CaO
3(a)(ii) (step) 3
3(a)(iii) thermal decomposition
3(a)(iv) heating
3(a)(v) Ca(OH)2 + CO2 → CaCO3 + H2O
3(a)(vi) M1 CO2 is acidic
M2 Ca(OH)2 is a base / alkali
3(b) MgCO3 + 2HNO3 → Mg(NO3)2 + H2O + CO2
M1 Mg(NO3)2
M2 rest of equation
3(c)
