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Chemistry · Paper 2A · 2024

2 questions

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Questions (2)

Section A

1. 0 marks

A sample of 500 cm$^3$ of vinegar solution consists 3 g of organic acid with a general formula R-COOH where R is an alkyl group. The amount of the acid in vinegar is determined through titration with a standard solution of a base made by dissolving 1.2 g of NaOH with distilled water to make 500 cm$^3$ solution. Use phenolphthalein (POP) indicator to carry out the experiment using the given procedure, then answer the questions that follow. Procedure (i) Fill the burette with vinegar solution. (ii) Use the pipette to transfer 25 cm$^3$ or 20 cm$^3$ of the base solution into a clean and dry conical flask and add three drops of POP. (iii) Titrate the resulting mixture against vinegar solution. (iv) Repeat procedure (i) to (iii) to obtain three more readings and record the results in a tabular form.

(a) Calculate: (i) the concentration of the base in mol/dm$^3$. (ii) the molarity of the organic acid. (iii) the molecular mass of the organic acid. 0 mk
(a) Describe briefly the procedure you would follow to determine the molar mass of the unknown solid in solution A by titrating it against solution B. 10 mk
(a(i)) the concentration of the base in mol/dm³. 1 mk
(a(ii)) the molarity of the organic acid. 1 mk
(b) If R in the acid is represented by C$_n$H$_{2n+1}$, find the value of n in the formula unit. 0 mk
(a(iii) the molecular mass of the organic acid. 1 mk
(c) Write the structural formula of the acid and give its IUPAC name. 0 mk
(d) Write the reaction between the organic acid and ethanol in the presence of H$_2$SO$_4$. 0 mk
(b) If R in the acid is represented by CnH2n+1, find the value of n in the formula unit. 1 mk
(e) Give two natural sources of the organic acid present in vinegar. 0 mk
(c) Write the structural formula of the acid and give its IUPAC name. 1 mk
(d) Write the reaction between the organic acid and ethanol in the presence of H₂SO₄. 1 mk
(f) Calculate the molar mass of the unknown solid (H₂X). 2 mk
(e) Give two natural sources of the organic acid present in vinegar. 1 mk

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2. 0 marks

Sample PP contains one cation and one anion. Carry out systematic qualitative analysis procedures, to identify the cation and anion in sample PP. Record carefully your experiments, observations and inferences as indicated in the experimental table.

Experimental Table
SNExperimentsObservationsInferences
(a) What are the cation and anion in the sample? 0 mk
(a) What are the cation and anion in the sample? 1 mk
(b) Write the molecular formula of the sample. 1 mk
(b) Write the molecular formula of the sample. 0 mk
(c) Mention two properties of the cation identified. 0 mk
(c) Mention two properties of the cation identified. 1 mk
(d) To about 2 cm³ of Solution R, add 2-3 drops of dilute ammonia solution (NH₃(aq)). 4 mk
(e) To about 2 cm³ of Solution R, add 2-3 drops of sodium hydroxide solution (NaOH). 4 mk
(f) To about 2 cm³ of Solution R, add 2 cm³ of Solution Q (Silver Nitrate). 5 mk
(g) Divide the remaining Solution R into three test tubes. Test tube 1: Add 2 cm³ of barium chloride solution (BaCl₂). 1 mk
(h) Test tube 2: Add 2 cm³ of barium chloride solution (BaCl₂) followed by a few drops of dilute hydrochloric acid (HCl). 1 mk
(i) Test tube 3: Add 2 cm³ of barium chloride solution (BaCl₂) followed by a few drops of dilute sulfuric acid (H₂SO₄). 1 mk
(j) From the observations, identify the cation and anion present in solid P. 4 mk

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