KCSE CHEMISTRY QUESTIONS AND ANSWERS PER TOPIC
How would you obtain a sample of pure iodine from a mixture of iodine and lead sulphate?
Expected Response
Heat the mixture iodine sublimes and can be collected from the cool part of the test tube.
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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.
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
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
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