KCSE CHEMISTRY QUESTIONS AND ANSWERS PER TOPIC
ANSWERS
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Zinc oxide reacts with acids and alkalis
a) Write the equation for the reaction between zinc oxide and: i) Dilute sulphuric acid ii) Sodium hydroxide solution b) What property of zinc oxide is shown by the reaction in (a) above? a) Give the name of each of the processes described below which takes place when salts are exposed to air for sometime. i) Anhydrous copper sulphate becomes wet (1mk) ii) Magnesium chloride forms an aqueous solution (1mk) iii) Fresh crystals of sodium carbonate, Na2CO3. 10H2O (1mk) b) Write the formula of the complex ion formed in each of the reactions described below. (i) Zinc metal dissolves in hot alkaline solution (1mk) (ii) Copper hydroxide dissolves in excess ammonia solution. (1 mk) (c) A hydrated salt has the following composition by mass. Iron 20.2% Oxygen 23.0%, sulphur 11.5%, water 45.3 %. Its relative formula mass is 278. (i) Determine the formula of the hydrated salt.. (3mks) (Fe=56, S=32; O = 16, H =1) (ii) 6.95gm of the hydrates salt were dissolved in distilled water and the total volume made to 250 cm3 of solution. Calculate the concentration of the salt solution in moles per litre.
a) at 250°C , 50g of potassium were added to 100gm of water to make a saturated solution. What is meant by a saturated solution?
b) The table below gives the solubilities of potassium nitrate at different temperatures.
(i) Plot graph of the solubility of potassium nitrate (vertical axis) against temperature
(ii) Using the graph: I Determine the solubility of potassium nitrate at 15°C II Determine the mass of potassium nitrate that remained undissolved given that 80g of potassium nitrate were added to 100cm3 of water and warmed to 40°C. c) Determine the molar concentration of potassium nitrate at 15°C (Assume there is no change in density of water at this temperature) (K = 39. 0; N= 14.0; O = 16.0)
In an experiment, a student put equal volumes of mixtures of ethanoic acid in water and ethanoic acid in hexane in two test – tubes as shown below. In each test tube, equal amounts of solid sodium hydrogen carbonate were added.
a) State the observation which was made in each test – tube
Test tube 1 Test tube 2 b) Explain the observation in (a) above
Starting with aluminium sulphate, describe how a solid sample of aluminium hydroxide could be prepared.
answers
Explain how you would obtain solid carbonate from a mixture of lead carbonate and sodium carbonate powders. (3mks)
Expected Response
Dissolve in water, filter to remove lead carbonate as a residue, evaporate filter to saturation and allow to cool. Crystallization to take place. Filter the crystals and dry. Evaporate to dryness
answer
(a) what method can be used to separate a mixture of ethanol and propanol?
(b) (i) Explain how a solid mixture of sulphur and sodium chloride can be separated Into solid sulphur and solid chloride (c) The table below gives the solubilities of potassium bromide and potassium sulphate at 00C and 400C
When an aqueous mixture containing 60g of potassium and 7 g of potassium sulphate in 10g of water at 800C was cooled to 00C some crystals were formed
(i) Identify the crystals (ii) Determine the mass of the crystals formed (iii) Name the method used to obtain the crystals (iv) Suggest one industrial application of the method named in (iii) above
The following tests were carried out on three separate portions of a colourless solution S
(a) From the information in test (i), name a cation, which is not present in solution S.
(b) Identify a cation, which is likely to be present in solution S (c) Write an ionic equation for the reaction, which takes place in test (ii) |
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