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INTERIM JOINT MATRICULATION BOARD EXAMINATION 2022
SUBJECT: CHEMISTRY PAPER III (ALTERNATIVE A)
TIME ALLOWED: THREE HOURS (3 HRS)
INSTRUCTIONS:
i. Answer ALL questions. Question (1) carries 50 marks while question (2) carries 30 marks. Textbooks, practical manuals and any other instructional materials are PROHIBITED in the examination hall.
ii. The use of a scientific programmable calculator is NOT ALLOWED.
iii. The atomic masses of the following elements are provided:
H = 1, C = 12, O = 16, K = 39, Cl = 35.5
1. You are provided with the following materials:
Solution A contains 2.30g of a weak acid, HX (Ka = 1.8 x 10-4) in 250cm3 solution.
Solution B contains 2.80g of potassium hydroxide and KOH in a 500cm3 solution.
Phenolphthalein indicator
(a) Procedure:
(i) Pipette 20 or 25cm3 of solution B into a conical flask. Add 2 0r 3 drops of phenolphthalein indicator ad titrate against solution A from a burette to a colourless endpoint.
(ii) Repeat the above procedure twice more using fresh portions of solution B. (16 marks)
(iii) Calculate the average titer. (2 marks)
(iv) Write the equation of the reaction. (2 marks)
(b) Calculate the following:
(i) molar concentration of KOH in solution B; (3 marks)
(ii) number of moles of KOH titrated; (3 marks)
(iii) number of moles HX consumed in the titration; (2 marks)
(iv) molar concentration of HX in solution A; (3 marks)
(v) molar mass of weak acid; (3 marks)
(vi) relative molecular mass of X in the formula HX; (2 marks)
(vii) pH of solution A. (4 marks)
(c) (i) Distinguish between the endpoint and the equivalence point in acid-base volumetric analysis. (4 marks)
(ii) Explain why phenolphthalein and not methyl orange is used in the above titration. (3 marks)
(iii) Give one major source of error in the experiment (a) above. (1 mark)
(iv) Give two common features of all volumetric analyses. (2 marks)
2. Carry out the following test and record your observations in inferences clearly, using the normal laboratory format. Credit will be given for Careful Observations clearly recorded and Explanatory Notes to account for observed reactions.
A. You are provided with sample A1 = Benzoic acid.
(a) Record the physical characteristics of the sample.
(b) Solubility test: with small quantities of the sample in separate test tubes, determine the solubility of the sample in:
(i) water
(ii) dilute hydrochloric acid
(iii) dilute sodium hydroxide
- Functional group test:
- Using a cleaned spatula, heat a small quantity of the sample in a Bunsen Burner flame,
- To a small quantity of the sample dissolved in ethanol, add a small amount of NaHCO3, warm the resulting mixture and note any gas evolution. If gas is evolved, test its reaction with lime water.
- To a small quantity of the sample dissolved in ethanol, add 1ml of H2SO4 and warm the resulting mixture. Perceive the odour of the mixture by blowing air with your hand across the mouth of the reaction test tube.
- Dissolve a small amount of the sample in ethanol. Dip a moist red litmus paper into a dilute solution of NaOH or NH3, the colour changes to blue. Then dip this litmus paper into the sample solution. (15 marks)
B. You are provided with sample A2 = Copper(II)trinitrate(V).
(a) Carry out two (2) confirmatory tests for the cation (b) Carry out two (2) distinguishing tests for the anion. (15 marks)
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