Cambridge IGCSE Chemistry - 0620 - Supplement Paper 4 2011 Winter Zone 3

Use your copy of the Periodic Table to answer these questions.
(a) Choose an element from the Periodic Table to match each description. You may give either the name or the symbol.
(i) It is the most reactive metal. ...................................................... [1]
(ii) It is the only non-metal which is a liquid at r.t.p.. ............................. [1]
(iii) An isotope of this element is used as a fuel in nuclear reactors. .............. [1]
(iv) This Group VII element is a solid at r.t.p.. .............................................. [1]
(v) This element is in Group V and Period 4. .................................................. [1]
(vi) This unreactive gas is used to fill lamps. ............................................... [1]
(b) Predict the formula of each of the following compounds.
(i) germanium oxide .....................................................................................
(ii) tellurium bromide .................................................................................... [2]
(c) Give the formula of each of the following ions.
(i) strontium ........................................................................................................
(ii) fluoride ............................................................................................................ [2]

(a) (i) Explain the terms:

monomer .................................................................................................................................
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condensation polymerisation .....................................................................................................
.................................................................................................................................................. [2]

(ii) Draw the structural formula of starch to include three monomer units.
Glucose, the monomer, can be represented as HO——OH . [3]

(b) Starch can be hydrolysed to simple sugars by heating with dilute sulfuric acid or by warming with a dilute solution of saliva. The reaction can be catalysed by $H^+$ ions from the acid or by the enzymes in saliva.

(i) What is an enzyme?
...................................................................................................................... [1]

(ii) Explain why, if the saliva / starch mixture is heated above 70°C, the hydrolysis stops.
...................................................................................................................... [1]

(iii) The complete acid-catalysed hydrolysis of starch forms only glucose. The partial acid-catalysed hydrolysis of starch forms a mixture of sugars which includes glucose. Describe how you could identify the different sugars in this mixture.
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Fertilisers are used to promote plant growth.
Two fertilisers are ammonium phosphate, $(\text{NH}_4)_3\text{PO}_4$, and calcium dihydrogenphosphate, Ca(H$_2$PO$_4$)$_2$.
(a) Describe a test to distinguish between these two fertilisers.
test ..................................................................................................................
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[2]
result ................................................................................................................
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[1]
(b) Many fertilisers are manufactured from ammonia. Describe how ammonia is made in the Haber process. Give the essential conditions and an equation for the process.
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[4]
(c) State the essential plant nutrient not supplied by ammonium phosphate.
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[1]
(d) The soluble compound, calcium dihydrogenphosphate is made by heating the insoluble mineral rock phosphate, Ca$_3$(PO$_4$)$_2$, with sulfuric acid.
(i) Why would rock phosphate not be effective as a fertiliser?
........................................................................................................................
[1]
(ii) The phosphate ion, $\text{PO}_4^{3-}$, from the rock phosphate is changed into the dihydrogenphosphate ion, $\text{H}_2\text{PO}_4^{-}$.
\[ PO_4^{3-} + 2\text{H}_2\text{SO}_4 \rightarrow \text{H}_2\text{PO}_4^{-} + 2\text{HSO}_4^{-} \]
What type of reagent is the phosphate ion? Give a reason for your choice.
........................................................................................................................
........................................................................................................................
[2]
(e) The extensive use of fertilisers and possibly the effect of acid rain tend to increase the acidity of the soil. State why it is necessary to control soil acidity and explain how this can be done.
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[2]

(a) Steel rusting is an example of an oxidation reaction.
(i) Define the term steel.
........................................................................................................................................
........................................................................................................................................ [2]
(ii) Define oxidation in terms of electron transfer.
........................................................................................................................................ [1]

(b) A method of preventing steel rusting is sacrificial protection.



Give an explanation, in terms of electron transfer, why the steel does not rust.
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........................................................................................................................................ [2]

(c) Another method of preventing steel rusting is cathodic protection.



(i) Write an equation for the formation of the gas given off at the steel cathode during cathodic protection.
........................................................................................................................................ [2]
(ii) Give one difference between the two methods.
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........................................................................................................................................ [2]

The reactions in this question are all examples of photochemical reactions.
(a) Explain the phrase photochemical reaction.
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........................................................................................................................................... [2]
(b) Many millions of years ago, the Earth's atmosphere was rich in carbon dioxide and contained negligible amounts of oxygen. After the appearance of green plant-like bacteria, the proportions of these two gases in the atmosphere changed.
(i) What are the approximate percentages of these two gases in the atmosphere now?
carbon dioxide = ..................................................................................................................
oxygen = .............................................................................................................................. [2]
(ii) Explain how the green plant-like bacteria changed the composition of the atmosphere.
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........................................................................................................................................ [4]
(c) The reduction of silver(I) bromide to silver is the basis of film photography.

An opaque object is placed on a piece of paper coated with silver(I) bromide which is then exposed to a bright light. The light is switched off and the opaque object removed.
Explain how the image is formed.
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........................................................................................................................................ [4]

Nickel is a transition element.

(a) Predict three differences in the chemical properties of nickel and barium.

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..................................................................................................................................................... [3]

(b) Nickel ores are converted into nickel(II) oxide. This can be reduced to impure nickel by heating with carbon. The nickel is purified by the following reversible reaction.

$$ \text{Ni(s) + 4CO(g) } \rightleftharpoons \text{ Ni(CO)}_4\text{(g)} $$
nickel carbonyl

(i) Impure nickel is heated at 60°C. The forward reaction occurs.

$$ \text{Ni(s) + 4CO(g) } \rightarrow \text{ Ni(CO)}_4\text{(g)} $$
impure

The nickel carbonyl, a gas, moves into a hotter chamber at 200°C. The backward reaction occurs and the nickel carbonyl decomposes.

$$ \text{Ni(CO)}_4\text{(g) } \rightarrow \text{ Ni(s) + 4CO(g)} $$
pure

Is the forward reaction exothermic or endothermic? Give a reason for your answer.

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.....................................................................................................................................................
........................................................................................................................... [2]

(ii) Explain why the forward reaction is favoured by an increase in pressure.

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........................................................................................................................... [2]

(iii) Suggest what happens to the impurities.

........................................................................................................................... [1]

(iv) Suggest another method of refining nickel. Give a brief description of the method which you have suggested. A labelled diagram is acceptable.
........................................................................................................................... [4]

The alkenes are a series of unsaturated hydrocarbons. They have the general molecular formula $C_nH_{2n}$.
(a) Deduce the molecular formula of an alkene which has a relative molecular mass of 126. Show your working.
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(b) The structural formula of propene is drawn below.

(i) Draw a diagram showing the arrangement of the valency electrons in one molecule
of this covalent compound.
Use x to represent an electron from an atom of carbon.
Use o to represent an electron from an atom of hydrogen.
(ii) Draw the structure of the polymer formed from propene
..................................
(iii) Bond energy is the amount of energy, in kJ, which must be supplied to break one
mole of the bond.
[Table_1]
Use the data in the table to show that the following reaction is exothermic.

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(c) This question is concerned with some of the addition reactions of but-1-ene.
(i) Name the product formed when but-1-ene reacts with water.
..............................................................................................................................
(ii) Complete the equation.
$CH_3 - CH_2 - CH = CH_2 + Br_2 \rightarrow$ .........................................................................
(iii) Deduce the formula of the compound which reacts with but-1-ene to form 1-iodobutane.
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