KCSE CHEMISTRY QUESTIONS AND ANSWERS PER TOPIC
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:
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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
(a) A student was supplied with a colourless liquid suspected to be water
The flow chart below shows the various stages of water treatment. Study it and answer the questions that follow
II Addition of sodium hypochlorite (c) It was confirmed that magnesium sulphate was present in the tap water
(a) The following diagrams show the structures of two allotropes of carbon. Study them and answer the questions that follow
(i) Name allotrope
M N (ii) Give one use of N (iii) Which allotrope conducts electricity? Explain
(b) In an experiment, carbon dioxide gas as passed over heated charcoal and the gas produced collected as shown in the diagram below
(i) Write an equation for the reaction that took place in the combustion tube
(ii) Name another substance that can be used instead of sodium hydroxide (iii) Describe a sample chemical test that can be used to distinguish between carbon dioxide and carbon monoxide (iv) Give one use of carbon monoxide
(a) Give the names of the following compounds
Name the type of bromination reaction that takes place in: (i) and (ii)
(d) The polymerization of tetra flouroathene (C2H4) is similar to that of ethane ( C2H4)
(e) State any two advantages that synthetic polymers have over natural polymers
(a)
(b) A sample of hydrogen chloride gas was dissolved in water to make 250cm3 of solution required 46 cm3 of 11.0M Sodium hydroxide for complete neutralization.
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.
​(a) The grid given below represents part of the periodic table. Study it and answer the questions that follow. (the letters do not represents the actual symbol of the elements)
​(b) Study the information in the table below and answer the questions that follow (the letters do not represent the actual symbol of the substances)
II. By downward displacement of air? (Density of air is 1.29 x 10-3g/cm3 at room temperature. Related Chemistry Questions and Answers on Chemical Families Form 2 Level
​The flow chart below illustrate the industrial extraction of lead metal. Study it and answer the questions that follow
(a)
(c) State one use of lead other than the making of lead pipes Related Chemistry Questions and Answers on Metals Form 4 Level
1 (a) The diagram below represents a mercury cell that can be used in the industrial manufacture of sodium hydroxide. Study it and answer the question that follow
In an experiment, ammonia chloride was heated in a test tube. A moist red litmus paper placed at the mouth of the test tube first changed blue then red. Explain these observations
Expected Response
NH4Cl decomposes to form NH3(g) and HCl(g).Ammonia diffuses faster than HCl because its light. Ammonia is basic and thus red litmus paper turns blue while HCl is acid thus blue litmus turns red.
Explain why it is not advisable to leave a Jiko with burning charcoal in a closed room where one is sleeping.
Expected Response
The supply of oxygen in the room will be limited leading to formation of CO which is poisonous.
Hydrogen and fluorine react according to the equation below
When a solid sample of sulphur is heated in a test tube, it changes into a liquid, which flows easily. On further heating, the liquid darkness and does not flow easily. Explain these observations.
Expected Response
Solid sulphur is made of S8 rings. It melts into aliquid of S8 rings, On further heating the rings open up to form long chains of sulphur atoms, which then entangle making it viscous and dark, or sulphur melts into S8 molecules. The molecules join up to form long chain which entangle making it viscous and dark
Study the information in the table below and answer the questions that follow. The letters do not represent the actual symbols of the elements)
Select an element which
Expected Response
Name another gas, which is used together with oxygen in welding
Expected Response
Acet5ylene (ethyne) or Hydrogen
Pentane and ethanol are miscible. Describe how water could be used to separate a mixture of pentane and ethanol
Expected Response
20. Add water to the mixture in a separating funnel. Ethanol dissolves while pentane does not. Allow the mixture to separate in two layers. Open the tap to drain the lower aqueous layer. Distil the water ethanol mixture to get ethanol.
The curves below were obtained when two equal volumes of hydrogen peroxide of the same concentration were allowed to decompose separately. In one case, manganese (IV) oxide was added to the hydrogen peroxide
Which curve represents the decomposition of hydrogen peroxide with manganese (IV) oxide? Explain
Expected Response
19. I – Manganese (iv) Oxide is a catalyst and increases the rate of decomposition of the hydrogen peroxide.
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