KCSE CHEMISTRY QUESTIONS AND ANSWERS PER TOPIC
Sample solutions of salt were labeled as I,II, III and IV. The actual solutions, not in that order are lead nitrate, zinc sulphate potassium chloride and calcium chloride.
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A weighed sample of crystalline sodium carbonate (Na2CO3. H2O) was heated in a crucible until there was no further change in mass. Calculate the number of moles (n) of the water of crystallization
The apparatus shown in the diagram below were used to investigate the products formed when concentrated sodium chloride was electrolysed using inert electrodes.
(a) Write the equation for the reaction that takes place at electrode A.
(b) If the concentrated sodium chloride was replaced with dilute sodium chloride, what product would be formed at electrode A? Explain.
(a) The electronic arrangement of the ion of element Q is 2.8.8. If the formula of the ion is Q3-,state the group and period to which Q belongs.
Group: Period: (b) Helium, neon and argon belong to group 8 of the periodic table. Give: (i) the general name of these elements; (ii) one use of these elements.
Describe two chemical tests that can be used to distinguish ethanol from ethanoic acid.
Describe how a solid sample of potassium sulphate can be prepared starting with 200cm3 of 2M potassium hydroxide.
The following set up of three test-tubes was used to investigate rusting of iron.
Study it and answer the questions that follow.
(a) Give a reason why rusting did not occur in test-tube C.
(b) Aluminium is used to protect iron sheets from rusting. Explain two ways in which aluminium protects iron from rusting.
ANSWERS
(a) No air due to boiling.
(b) Aluminium being very reactive forms a layer of Al2O3 on the metal making it impervious to moisture. Aluminium being more reactive than iron protects the iron through sacrificial protection cathodic protection.
Describe how the percentage by mass of copper in copper carbonate can be determined.
Aluminium is both malleable and ductile,
(a) What is meant by? (i) malleable; (ii) ductible. (b) State one use of aluminium based on: (i) malleability (ii) ductility
ANSWERS
(a) (i) Malleable - Can be hammed into sheets
(ii) Ductile - Can be drawn into wires (b) (i) Saucepans (ii) Electrical transmission lines
Give two uses of the polymer polystyrene.
ANSWERS
Draw and name the isomers of pentane.
The set up shown below was used to investigate a property of hydrogen gas.
State and explain the observation that would be made in the glass tube if beaker A was filled with hydrogen gas.
ANSWERS
Acidified potassium manganate (VII) solution is decolourised when sulplur (IV) oxide is bubbled through it. The equation for the reaction is given below.
2H2O(1) + 5S02(g) + 2KMnO4(aq) —►K2SO4(aq) + 2MnSO4(aq)+ 2H2SO4(aq) (a) Which reactant is oxidised? Explain. (b) Other than the manufacture of sulphuric (VI) acid, state one other use of sulphur (IV) oxide.
Give a reason why phosphorus is stored under water.
Expected Response
To keep away air/ oxygen which would react with it
Study the scheme below and answer the questions that follow
a) Identify solid E.
b) Write an ionic equation for the reaction in step II that produces solid F.
The electronic structures for elements represented by letters A,B,C,D are
A=2 .8.6 B 2.8.2 C 2. 8. 1 D 2. 8. 8. a) Select the element which forms:
In an experiment, 0.8gm of magnesium of powder were reacted with excess dilute sulphuric acid at 250C . The time for the reaction to come to completion was recorded. The experiment was repeated at 400C. In which experiment was the time taken shorter? Explain your answer.
Expected Response
Experiment II. At a high temperature the particles have more energy, hence rate of high energy collisions increase.
Study the nuclear reaction given below and answer the questions that follow
Study the energy level diagram below and answer the questions that follow.
(a) Give the name of ΔHA
(b) How can ΔHB be reduced? Give a reason.
ANSWERS
(a) Heat of reaction
(b) Using a catalyst Catalyst reduce activation energy.
Use the following information on substances S, T, V and hydrogen to answer the questions that follow:
(i) T displaces V from a solution containing V ions. (ii) Hydrogen reacts with the heated oxide of S but has no effect on heated oxide of V. (a) Arrange substances S, T, V and hydrogen in the order of increasing reactivity. (b) If T and V are divalent metals, write an ionic equation for the reaction in (i) above.
Below is a representation of an electrochemical cell.
Calculate the E.M.F of the electrochemical cell.
Distinguish between ionisation energy and electron affinity of an element.
ANSWERS
A dynamic equilibrium is established when hydrogen and carbon (IV) oxide react as shown below:
What is the effect of adding powdered iron catalyst on the position of the equilibrium?
Give a reason.
ANSWERS
Study the flow chart below and answer the questions that follow.
(a) Name a suitable drying agent for ammonia.
(b) Describe one chemical test for ammonia. (c) Name X.
ANSWERS
(a) Calcium Oxide
(b) Expose ammonia to hydrogen chloride gas, dense white fumes of ammonium chloride are observed. (c)Steam/water .
State and explain the function of tartaric acid in baking powder
Expected Response
It reacts with NaHCO3 to form CO2 which causes the dough to rise.
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