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Chemistry Paper 3 Question Paper
Chemistry Paper 3
Course:Secondary Level
Institution: Kcse question papers
Exam Year:2011
You are provided with:
• 1.60g of solid A, a dibasic acid.
• Solution B containing 4.75g per litre of salt B.
• Aqueous sodium hydroxide, solution C.
• Phenolphthalein indicator.
You are required to prepare a solution of solid A and use it to determine the:-
• Concentration of sodium hydroxide, solution C
• React salt B with excess sodium hydroxide and then determine the relative molecular mass of salt B.
Procedure I
(a) Using a burette, place 25.0cm3 of solution B in each of two 250ml conical flasks.
Using a pipette and pipette filler, add 25 .Ocm3 of solution C to each of the two conical flasks. (The sodium hydroxide added is in excess). Label the conical flasks 1 and 2.
(b) Heat the contents of the first conical flask to boiling and then let the mixture boil for 5 minutes. Allow the mixture to cool.
(c) Repeat procedure (b) with the second conical flask.
While the mixtures are cooling, proceed with procedure II. Procedure II
(a) Place all of solid A in a 250 ml volumetric flask. Add about 150cm3 of distilled water, shake well to dissolve the solid and then add water to make up to the mark. Label this as solution A.
(b) Place solution A in a clean burette. Using a pipette and pipette filler, place 25.0cm3 of solution C in a 250ml conical flask. Add 2 drops of phenolphthalein indicator and titrate with solution A. Record your results in Table 1. Repeat the titration two more times and complete the table.
(i) Average volume of solution A used: (1/2 marks)
(ii) Concentration in moles per litre of the dibasic acid in solution A; (2 marks)
(Relative molecular mass of A is 126).
(iii) Moles of the dibasic acid used; (1 mark)
(iv) moles of sodium hydroxide in 25.0cm3 of solution C. (1 mark)
(v) Concentration of sodium hydroxide in moles per litre. (2 marks)
Calculate the:-
(i) average volume of solution A used; (1/2 marks)
(ii) moles of the dibasic acid used; (1 mark)
(iii) moles of sodium hydroxide that reacted with the dibasic acid. (1 mark)
(iv) moles of sodium hydroxide that reacted with 25.0cm3 of salt B in solution B;
(2 marks)
(v) Given that 1 mole of salt B reacts with 2 moles of sodium hydroxide, calculate the:
(1 mark)
I. number of moles of salt B in 25.0cm3 of solution B;
II. concentration in moles per litre of salt B in solution B; (1 mark)
III. Relative molecular mass of salt B; (2 marks)
2. (a) You are provided with solid D. Carry out the following tests and write your observations and inferences in the spaces provided.
(i) Place about one half of solid D in a test-tube and heat it strongly. Test any gases produced with both red and blue litmus papers.
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