Cambridge IGCSE Chemistry - 0620 - Supplement Paper 4 2015 Winter Zone 2

(a) Predict the formulae of the following compounds.
(i) nitrogen fluoride ...................................
(ii) phosphorus sulfide ................................................. [2]

(b) Deduce the formulae of the following ions.
(i) selenide ...................................
(ii) gallium ................................................. [2]

(c) Use the following ions to determine the formulae of the compounds.

ions: OH⁻, Cr³⁺, Ba²⁺, SO₄²⁻
compounds:
(i) chromium(III) sulfate ...................................
(ii) barium hydroxide ................................................. [2]

(a) Polluted air contains two oxides of carbon and two oxides of nitrogen. A major source of these pollutants is motor vehicles.

(i) Describe how carbon dioxide and carbon monoxide are formed in motor vehicle engines.
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(ii) State \textbf{one} adverse effect of each of these gases.
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(iii) Nitrogen monoxide, NO, is released by motor vehicle exhausts.
Explain how nitrogen monoxide is formed in motor vehicle engines.
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(iv) When nitrogen monoxide is released into the atmosphere, nitrogen dioxide, NO$_2$, is formed.
Suggest an explanation why this happens.
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(b) Predict the possible adverse effect on the environment when this non-metal oxide, NO$_2$, reacts with water and oxygen.
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(c) How are the amounts of carbon monoxide and nitrogen monoxide emitted by modern motor vehicles reduced? Include an equation in your answer.
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(a) Stage 1 Zinc oxide is made from zinc blende.

Describe how this is done and write a word equation for the reaction.
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(b) Stage 2 Zinc oxide is reduced to zinc.

Write a word equation for the reduction of zinc oxide by coke.
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(c) The zinc produced by this process is impure. It can be purified by electrolysis using a method
which is similar to the purification of copper. Under the conditions used in the process, zinc is
the product at the negative electrode (cathode).

Complete the following description of this purification.

The electrolyte is aqueous ........................................................... . [1]
The negative electrode (cathode) is made of ............................................... . [1]
The positive electrode (anode) is impure zinc.
The equation for the reaction at the cathode is ............................................... . [1]
The equation for the reaction at the anode is ................................................. . [1]
Explain why the concentration of the electrolyte does not change.
............................................................................................[2]

(d) Brass is an alloy which contains zinc.

(i) Name the other metal in brass.
....................................................................................................................................................[1]

(ii) Suggest two reasons why an alloy such as brass is preferred to either of its constituent
metals.
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(e) In an experiment to investigate the rate of rusting of steel, three pieces of steel were used. One
piece of steel was completely coated with copper, one piece completely coated with zinc and
the third piece was left uncoated. All three pieces were left exposed to the atmosphere.

(i) Explain why the uncoated piece started to rust.
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(ii) The coating on both of the other two pieces was scratched, exposing the steel.



The piece of steel coated with zinc still did not rust but the copper-coated piece of steel
rusted very rapidly.

Explain these observations in terms of the formation of ions and the transfer of electrons.
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(a) Propane reacts with chlorine to form a mixture of chloropropanes. This is a photochemical reaction.
(i) What is meant by the phrase photochemical reaction?
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(ii) The products of this reaction include two isomers, one of which has the following structural formula.

Draw the structural formula of the other isomer. [1]
(iii) Explain why these two different compounds are isomers.
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(b) Bond breaking is an endothermic change and bond forming is an exothermic change.
Bond energy is the amount of energy in kJ/mol needed to break one mole of the specified bond.

Use the following bond energies to determine whether this reaction is exothermic or endothermic. You must show your reasoning.
[Table_1]
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(c) (i) Chloropropane can be hydrolysed to propanol, $\text{CH}_3\text{CH}_2\text{CH}_2\text{OH}$, by sodium hydroxide. Write the equation for this reaction.
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(ii) Propanol can be dehydrated. It loses a water molecule to form a hydrocarbon. Give the name and structural formula of this hydrocarbon.
name ...................................................
structural formula

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(iii) Propanol is oxidised to a carboxylic acid by acidified potassium manganate(VII). Deduce the name of this acid.
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(d) Propanol reacts with methanoic acid to form the ester propyl methanoate.
$$\text{CH}_3\text{CH}_2\text{CH}_2\text{OH} + \text{HCOOH} \rightarrow \text{HCOOCH}_2\text{CH}_2\text{CH}_3 + \text{H}_2\text{O}$$
4.0 g of methanoic acid was reacted with 6.0 g of propanol.
(i) Calculate the $M_r$ of methanoic acid = ............................................... [1]
(ii) Calculate the $M_r$ of propanol = ............................................... [1]
(iii) Determine which one is the limiting reagent. Show your reasoning.
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(iv) Calculate the maximum yield in grams of propyl methanoate, $M_r$ = 88.
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Iron is extracted from its ore, hematite, in a blast furnace.

Substances added to the furnace are:
• iron ore, hematite, containing impurities such as silica, $\text{SiO}_2$
• air
• coke, C
• limestone, $\text{CaCO}_3$

Substances formed in the blast furnace are:
• molten iron
• molten slag
• waste gases such as carbon dioxide

(a) State the \textbf{two} functions of the coke used in the blast furnace.
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(b) Write an equation for the conversion of hematite, $\text{Fe}_2\text{O}_3$, to iron.
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(c) Explain how the silica impurity is removed and separated from the molten iron.
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(d) The molten iron from the furnace is impure.
It contains impurities which include the element carbon.

Explain how the carbon is removed. Include an equation in your answer.
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The table below shows the elements in the third period of the Periodic Table, the number of electrons in their outer energy level, their oxidation state in their common compounds and their melting points.

[Table_1]

(a) Describe and explain the variation in oxidation state across the period.
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(b) The first three elements, Na, Mg and Al, are metals.
Describe the structure of a typical metal.
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(c) Explain why Na, Mg and Al are good conductors of electricity.
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[1]

(d) Which element exists as diatomic molecules of the type $X_2$?
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[1]

(e) Silicon has a similar structure to diamond.
Explain why silicon has the highest melting point in the period.
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[2]

(f) Sodium chloride is a crystalline solid with a high melting point. It dissolves in water to give a neutral solution. Phosphorus trichloride is a liquid at room temperature. It reacts with water to form an acidic solution.
Suggest an explanation for these differences in properties.
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[2]

(g) Describe how you could show that magnesium oxide is a basic oxide and not an amphoteric oxide.
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[2]

(h) Draw a dot-and-cross diagram showing the bonding in magnesium oxide. Show outer electrons only.
[3]