SECTION A: [5O MARKS]
Answer all questions in the spaces provided.
A1
(a) A learner observed that every time the laboratory assistant entered the laboratory, she
does certain things. Explain why she
(i) opens windows in the laboratory,
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……………………………………………………………………………………………………………………… [1]
(ii) removes high−heeled shoes and puts on flat and closed shoes,
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……………………………………………………………………………………………………………………… [1]
(iii) sweeps the laboratory without applying cobra and shining the floor,
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……………………………………………………………………………………………………………………… [1]
(iv) wears a lab coat while doing experiments in the laboratory?
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……………………………………………………………………………………………………………………… [1]
(b) Give one source of error when taking readings from a burette.
……………………………………………………………………………………………………………………………
……………………………………………………………………………………………………………………… [1]
[Total: 5 marks]
A2 (a) Study the following diagram.
(i) Name the apparatus shown. [1]
……………………………………………………………………………………………………………………… [1]
(ii) State two precautions which you must take when using this apparatus.
……………………………………………………………………………………………………………………………
……………………………………………………………………………………………………………………… [2]
(iii) State the use of the apparatus.
……………………………………………………………………………………………………………………… [1]
(b) Substance Q is a mixture of iron filings, sand and potassium iodide.
(i) Describe how a sample of pure crystals of potassium iodide can be
obtained from mixture Q.
………………………………………………………………………………………………………………………………
…………………………………………………………………………………………………………………… [2]
(ii) Describe how sand can be obtained from Q?
……………………………………………………………………………………………………………………………
……………………………………………………………………………………………………………………… [2]
[Total: 8 marks]
A3
(a) By means of dot and/or cross diagrams, show the full electronic structure of
(i) carbon,
(ii) oxygen,
(iii) carbon dioxide.
(b) Compounds are classified as ionic or covalent. Give two differences between ionic and
covalent compounds.
……………………………………………………………………………………………………………………………
……………………………………………………………………………………………………………………… [2]
[Total: 6 marks]
A4
(a) Using oxygen atoms, state the difference between valence electrons and valency.
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……………………………………………………………………………………………………………………… [2]
(b) Assuming oxygen uses only a fixed valency, deduce the valency of element X in the
following oxides;
(i) XO..................................................................................................
(ii) X03..................................................................................................
[1]
[1]
(c) 1 mol of a carbohydrate bums completely in oxygen producing 220g of carbon dioxide
and 90g of water. Determine the chemical formula of this carbohydrate. Note that the
ratio of H:O in every carbohydrate is 2:1.
[4]
One of the major uses of phosphorus is in the making of safety matches. A safety match
ignites when rubbed against the striking surface of a match box.
The contents of a match head are as follows;
− Phosphorus- P
− Potassium chlorate(V) - KCO,
− Sulphur - S
− a hydrocarbon wax
A5
(a) The friction between the match head and the striking surface generates enough heat for
the phosphorus to bum. Phosphorus burns to form phosphorus (V) oxide.
(i) State the molecular formula of phosphorus (V) oxide?
……………………………………………………………………………………………………………………… [2]
(ii) Suggest one chemical property of phosphorus (V) oxide.
……………………………………………………………………………………………………………………… [1]
(b) The heat from the combustion of phosphorus provides energy for the decomposition of
potassium chlorate (II) to oxygen and potassium chloride. Construct a balanced
chemical equation for the decomposition of potassium chlorate (V).
……………………………………………………………………………………………………………………… [1]
(c) The sulphur on the match head also ignites. Write a word equation for the combustion
of sulphur.
…………………………………………………………………………………………………………………………[1]
(d) Finally, the wax on the match head begins to combust. One compound in the wax has
the molecular formula of C21H44. Construct a balanced chemical equation for the
complete combustion of this hydrocarbon.
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……………………………………………………………………………………………………………………… [2]
[Total: 7 marks]
A6
Sodium, Na, is an element found in Group I of the Periodic Table. It reacts with chlorine to
form a salt, sodium chloride.
(a) In which Period of the Periodic Table is sodium found?
……………………………………………………………………………………………………………………….. [1]
(b) What common name is given to Group I elements?
………………………………………………………………………………………………………………………. [1]
(c) Which element would react more vigorous with chlorine between lithium and potassium?
Explain your answer.
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……………………………………………………………………………………………………………………………… [2]
(d) Give one physical property of Group I elements.
……………………………………………………………………………………………………………………………… [1]
[Total: 5 marls]
A7
(a) Each of the following statements is scientifically incorrect. But if one word is replaced by
a correct one, the statement becomes true. Identify the wrong word, underline it, and write
the correct word in the blank space provided.
(i) Acids produce hydroxide ions when dissolved in water.
……………………………………………………………………………………………………………………………… [1]
(ii) The reaction between hydrogen ions and hydroxide ions is called hydration.
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(iii) Zinc carbonate can react with both dilute hydrochloric acid and sodium hydroxide
solution.
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(iv) A dark blue solution is formed when excess of ammonia solution is added
to copper (II) hydroxide because ammonia is acting as a reducing agent.
……………………………………………………………………………………………………………………………… [1]
(b) If a solution of sodium hydroxide is added to another solution of zinc sulphate little by
little until in excess, state
(i) what you would finally physically see (observe)?
……………………………………………………………………………………………………………………………… [1]
(ii) the product responsible for the observation in (b)(i)
……………………………………………………………………………………………………………………………… [1]
[Total: 6 marks]
A8
The following table gives the composition of gases in unpolluted air.
Gas
Percentage (%)composition by
volume
R
79
Oxygen
Other gases
1
(a) In the table shown, write the value that represents percentage composition by volume
of oxygen in air.
(b) State one physical property of oxygen.
……………………………………………………………………………………………………………………………… [1]
(c) What is the chemical test for oxygen?
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(d) Give the industrial process used to manufacture gas R.
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(e) State one use of gas R.
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[Total: 5 marks]
SECTION B: (30 MARKS)
Answer three questions from this section. Write your answers in the Answer
Booklet provided.
B1
The following diagram represents a cell used for extraction of aluminium from alumina.
(a) Alumina is first dissolved in substance X before it is used as an electrolyte.
(i) Identify substance X. [1]
(ii) Give two reasons why alumina is dissolved in substance X. [2]
(b) The anode and cathode are made of the same material.
(i) Name the material.
[1]
(ii) Explain with the help of an equation why the anode is replaced at intervals. [2]
(c) Give an equation for the reaction that takes place at the cathode. [1]
(d) Give two reasons why aluminium is ideal for making pots. [2]
(e) Suggest a reason why aluminium is mostly used in form of an alloy. [1]
[Total: 10 marks]
B2
Methane burns in air producing carbon dioxide, water and heat energy.
(a) Construct a balanced equation including state symbols for this reaction. [2]
(b) Compare the energy of reactants and products for this reaction. [1]
(c) Copy and complete this energy diagram for this reaction indicating:
− activation energy
− overall energy change, ΔH
− energy needed to break bonds
− energy given out when new bonds are forming
Energy (kJ/mol)
CO2(g) + 2H2O(l)
[5]
Reaction path
(d) When 1 mol of methane bums in oxygen, the energy change is -900kJ/mol.
How much energy is given out when 1g of methane burns? [2]
[Total: 10 marks]
B3
Electrolytic cells and simple cells may operate in different or similar ways.
(a) Give one of such
(i) differences, [1]
(ii) similarities.
[1 J
(b) During an electrolytic process (electrolysis), state the source of electrons that
(i) enter the electrolyte,
[1]
(ii) leave the electrolyte.
[1]
(c) A simple cell involves copper and magnesium electrodes dipped in their respective
electrolytes.
(i) State a suitable electrolyte in which
(a) copper is dipped, [1]
(b) magnesium is dipped. [1]
(ii) For this simple cell, construct the half reaction that occurs as
(a) anode reaction, [1]
(b) cathode reaction. [1]
Which of the two cells, electrolytic or simple cells would
(i) determine the reactivity of two different metals, [1]
(ii) involve selective discharge of ions. [1]
[Total: 10 marks]
B4
Ethyl ethanoate is an ester that is made from a carboxylic acid and an alcohol.
(a) (i) Draw the structural formula of ethyl ethanoate showing all the bonds. [1]
(ii) Identify the acid and alcohol in this reaction. [1]
(iii) Name the catalyst used in this reaction. [1]
(b) The following structure is for an artificial polymer.
(i) How many repeating units are shown in the part structure? [1]
(ii) Showing all bonds, draw the structure of the monomer used to make the polymer and
hence give the name of the polymer. [2]
(iii) What observations would be made if this monomer reacted with bromine solution? [1]
(iv) What kind of polymerisation does this monomer undergo? Give a reason for your
answer. [2]
[Total: 10 marks]