KCSE CHEMISTRY QUESTIONS AND ANSWERS PER TOPIC
State two factors which determine the stability of an isotope.
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Study the set – up below and answer the question that follows.
State and explain the observations that would be made when the circuit is completed.
In an experiment, a student put equal volumes of mixtures of ethanoic acid in water and ethanoic acid in hexane in two test – tubes as shown below. In each test tube, equal amounts of solid sodium hydrogen carbonate were added.
a) State the observation which was made in each test – tube
Test tube 1 Test tube 2 b) Explain the observation in (a) above
Starting with aluminium sulphate, describe how a solid sample of aluminium hydroxide could be prepared.
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a) The energy change that takes place when one mole of the compound is formed from its constituents elements in their state
b) 3x-286 = 2x-394-(277) 858 + 788+ 277 = 11369kjmol Explain why it is not advisable to use aqueous chloride solution as the salt bridge in the electrochemical cell formed between half cells, Pb2-(aq)/pb(s) E0 = 0.13V and CU2 + (aq) + (aq)/CU2+(aq)/Cu2(s) E0=0.34V (2mks)
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Sodium chloride will remove Pb from the insoluble pbC12. This affects the value of the cell voltage.
a) State how burning can be used to distinguish between ethane and ethyne.
Explain your answer. b) Draw the structural formula of the third member of the homologous series of ethyne. c) The flow chart below shows a series of reactions starting with ethanol. Study it and answer the questions that follow.
ii) Write the equation for the combustion of ethanol
iii) Explain why it is necessary to use high pressure to change gas B into the polymer iv) State one use of methane
The basic raw material for extraction of aluminium is bauxite
a) Name the method that is used to extract aluminium from bauxite b) Write the chemical formula of the major component of bauxite c) i) Name two major impurities in bauxite ii) Explain how the impurities in bauxite are removed d) Cryolite is used in the extraction of aluminium from bauxite. State its function f) Aluminium is a reactive metal yet utensils made of aluminium do not corrode easily. Explain this observation
Excess marble chips (calcium carbonate ) was put in a beaker containing 100cm3 of dilute hydrochloric acid. The beaker was then placed on a balance and the total loss in mass recorded after every two minutes as shown in the table below.
a) Why was there a loss in mass?
b) Calculate the average rate of loss in mass between: i) 0 and 2 minutes ii) 6 and 8 minutes iii) Explain the difference in the average rates of reaction in (b) (i) and (ii) above c) Write the equation for the reaction which takes place in the beaker d) State three ways in which the rate of the reaction above could be increased e) The solution in the beaker was evaporated to dryness what would happen if the open beaker and its contents were left in the laboratory overnight. f) Finally some water was added to the contents of the beaker. When aqueous sodium sulphate was added to the contents of the beaker, a white precipitate was formed. i) Identify the white precipitate ii) State one use of the substance identified in (f) (i) above
i) Identify the particles emitted in steps I and III
I II ii) Write the nuclear equation for the reaction which takes place in step V The table below give the percentages of a radioactive isotope of Bismuth that remains after decaying at different times. i) On the grid provided, plot a graph of the percentage of Bismuth remaining (Vertical axis) against time.
ii) Using the graph, determine the:
I. Half – life of the Bismuth isotope II. Original mass of the Bismuth isotope given that the mass that remained after 70 minutes was 0.16g d) Give one use of radioactive isotopes in medicine
a) The diagram below is a cross- section of a dry cell. Study it and answer the questions that follow.
i) On the diagram, show with a (+) sign the positive terminal
ii) Write the equation for the reaction in which electrons are produced
iii) The zinc can is lined with ammonium chloride and zinc chloride paste. iv) Give one advantage and one disadvantage of dry cells. b) The set – up below was used to (electrolyse roller lead (II) ionide.
i) State the observation that was made at the anode during the electrolysis.
Give a reason for your answer. ii) A current of 0.5 A was passed for two hours. Calculate the mass of lead that was deposited (Pb = 1F = 9,500C)
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Increase in pressure would shift the equilibrium to the left; since in pressure favors thereaction will produce less volume of gas
During purification of copper by electrolysis, 1.48g of copper were deposited when current was passed through aqueous copper(II) sulphate for 2 1/2 hours. Calculate (CU = 63.5, 1 Faraday = 96,500C).
An organic compound with the formula C4 H10 O reacts with potassium metal to give hydrogen gas and white solid
(a) Write the structural formula of the compound (b) To which homologous series does the compound belong? (c) Write the equation for the reaction between the compound and potassium metal
Brass is an alloy of zinc and copper. Give one use of brass
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(a) what is meant by heat of vaporization
(b) The boiling points of ethanol, propanol and butanol are 780C, 97.20C and 1170C. explain this trend
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