KCSE CHEMISTRY QUESTIONS AND ANSWERS PER TOPIC
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.
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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.
A given volume of ozone, (O3) diffused from a certain apparatus in 96 seconds. Calculate the time taken by an equal volume of carbon dioxide (CO2) to diffuse under the same conditions (O = 16.0, C = 12.0)
Study the set- up below and answer the questions that follow
(a) Write an equation for the reaction, which take place in the combustion tube
(b) What property of gas Z allows it to be collected as shown in the diagram
Compound Q is a solid with a giant ionic structure. In what form would the compound conduct an electric current
Expected Response
16. When dissolves in water or fused / molten state
State any two differences between luminous and non – luminous flames
The table below shows the tests carried out on separate samples of water drawn from a well and the results obtained
(a) Identify the cation and the anion present in the water
Cation Anion (b) Write an ionic equation for the reaction which takes place in test (iii) A radioactive isotope X2 decays by emitting two alpha (a) particles and one beta (β) to from 214 Bi 83 (a) What is the atomic number of X2? (b) After 112 days, 1/16 of the mass of X2 remained. Determine the half life of X2
Expected Response
20.0cm3 of a solution containing 4 gm per litre of sodium hydroxide was neutralized by 8.0cm3 of dilute sulphuric acid. Calculate the concentration of sulphuric acid in moles per litre (Na = 23.0, O = 16.0, H = 1.0)
A student set up the apparatus shown below to prepare ammonia gas and react it with copper (II) sulphate solution
(a) Identify solution V
(b) State the observations which were made in the beaker
Expected Response
Use the scheme below to answer the questions that follow
(a) Identify the solid
H J (b) State one commercial use of solid J
A hydrocarbon P was found to decolourise bromine water. On complete combustion of 2 moles of P, 6 moles of carbon dioxide and 6 moles of water were formed
Study the solubility curves below and answer the questions that follows
What happens when a solution containing 40gm of potassium chlorate and 40gm of potassium nitrate in 100gm of water at 900C is cooled to 400C? Explain
Give two reasons why helium is used in weather balloons
Expected Response
Starting with copper metal, describe how a solid samples of copper (II) carbonate can be prepared.
The equation below represents a redox reaction
a) Write down the equation for the reduction process
b) Which substance is oxidized
The information below relates to elements S,T,U and X. ( the letters do not represents the actual symbols of the elements.
Both T and X are in group II of the periodic Table) (b) Arrange the elements in order of their increasing reactivity
When a current of 1.5 amperes was passed though a cell containing m3+ ions of a metal M for 15 minutes, the mass of the cathode increased by 0.26g.
(1 Faraday = 96500 coulombs) (a) Calculate the quantity of electricity used (b) Determine the relative atomic mass of metal M
The simplified flow chart shows some of the steps in the manufacture of sodium carbonate by the Solvay process
(a) Identify substance L
(b) Name the process – taking place in step II (c) Write an equation for the reaction, which takes place in step III |
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