KCSE CHEMISTRY QUESTIONS AND ANSWERS PER TOPIC
Study the flow chart below and answer the questions that follow
(a) Name:
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For each of the following reactions, state the observation and write the formula of the
Compound responsible for the observation: a) Bromine water is added to aqueous potassium iodide; b) Excess aqueous ammonia is added to copper (II) hydroxide (precipitate).
ANSWERS
(a) Pale green solution turns yellow
(b) Sodium hydroxide Potassium hydroxide (c) Water
The column below was used do soften hard water
Expected Response
A beekeeper found that when stung by a bee, application of a little solution of hydrogen carbonate helped to relieve the irritation from the affected area. Explain.
Expected Response
Hardness of water may be removed by either boiling or addition of chemicals
a) write an equation to show how boiling removes hardness of water. b) name two chemicals that are used to remove hardness of water.
The scheme below shows some reaction sequence starting with solid N.
Expected Response
Distinguished between a strong and a weak acid. Give examples.
ANSWERS
(a)Amphoteric
(b)Lead (II), Zinc and Aluminium
ANSWER
A sample of water drawn from a river passing through an agricultural district was divided into two portions. The first portion gave a white precipitate when acidified barium chloride was added. The second portion when warmed with aqueous sodium hydroxide gave a colourless gas, which turned a moist red litmus paper blue.
Expected response
Add water to the solid mixture A dissolves while B does Not
(a) The elements nitrogen, phosphorous and potassium are essential for plant growth.
(i) Potassium in fertilizers may be in the form of potassium nitrate Describe how a sample of a fertilizer may be tested to find out if it contained nitrate ions. (ii) Calculate the mass of nitrogen present if a 25kg bag contained pure ammonium phosphate, (NH4)2 HPO4. (N = 14.0, H=1.0, P = 31.0, O = 16.0 (b) The table below shows the solubility of ammonium phosphate in water at different temperatures.
(i) On the grid provided, draw the solubility curve of ammonium phosphate (Temperature on x – axis)
(ii) Using the graph, determine the solubility of ammonium phosphate at 25°C (iii) 100g of a saturated solution of ammonium phosphate was prepared at 25°C I what is meant by a saturated solution? II Calculate the mass of ammonium phosphate which was used to prepare the saturated solution (c) The graph below shows how the PH value of soil in a farm changed over a period of time
(i) Describe how the pH of the soil can be determined
(ii) State one factor that may have been responsible for the change in the soil pH in the time interval AB
a) Explain why permanent hardness in water cannot be removed by boiling.
b) Name two methods that can be used to remove permanent hardness from water.
ANSWERS
(a) The calcium and magnesium compounds in this water can not be decomposed by heating i.e. CaCl2, CaSO4, MgSO4 and MgCl2
(b)Ionic exchange Uses sodium carbonate (washing soda) In an equation below, identify the reagent that acts as abase. Give a reason. H2O(aq) + H2O(l) → H3O(aq) + HO2-(aq)
Potassium sulphite solution was prepared and divided into two portions. The first portion gave a white precipitate when reacted with barium nitrate. On addition of dilute hydrochloric acid the white precipitate disappeared.
a) Write the formula of the compound which formed as the white precipitate. b) Write the equation for the reaction between dilute hydrochloric acid and the compound whose formula is written in (a) above. c) What observation would be made if one drop of potassium dichromate solution was added to the second portion followed by dilute hydrochloric acid?
Explain why anhydrous magnesium chloride is fairly soluble in organic solvents while anhydrous magnesium chloride is insoluble.
Expected Response
Aluminum chloride is covalent while magnesium chloride is ionic
a) starting from solid magnesium hydroxide.
b) Give one use of magnesium hydroxide.
Below is a list of oxides.MgO, N2O, K2O, CaO, and Al2O3.
Select: a) A neutral oxide b) A highly water soluble basic oxide c) An oxide which can react with both sodium hydroxide solution and dilute hydrochloric acid.
a) water from a town in Kenya is suspected to contain chloride ions but not sulphate ions.
Describe how the presence of the chloride ions in the water can be shown. b) State one advantage of drinking hard water rather than soft water.
ANSWERS
a)
Acidify water with nitric acid. Add aqueous lead nitrate. Formation of white PPt shows presence of CT b)provides essential minerals e.g Ca2+ |
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