WAEC SSCE - Chemistry - 2007 (Practical)

(a) State an indicator suitable for the titration of;

(i) dilute HCl and NaOH\(_{3(aq)}\)

(ii) dilute CH\(_3\)COOH and KOH\(_{(aq)}\)

(iii) dilute HCl and NH\(_{3(aq)}\).

Give a reason for your answer in each case.

(b) Calculate the volume of water that would be added to 50 cm\(^3\) of 0.10 mol dm\(^{-3}\) of HCI to dilute it to 0.010 mol dm \(^{-3}\)

(c) Name one gas that could be used to demonstrate the fountain experiment.

All your burette readings (initial and final) as well as the size size of your pipette, must be recorded but no account of experimental procedure is required. All calculations must be done in your answer book.

A is a solution containing \(1.04\text{ g HCl}\) per \(500\text{ cm}^3\) of solution. B was prepared by diluting \(50.0\text{ cm}^3\) of a saturated solution of \(\mathrm{Na}_2\mathrm{CO}_3\) at room temperature to \(1000\text{ cm}^3\)

(a) Put A into the burette and titrate it against \(20.0\text{ cm}^3\) or \(25.0\text{ cm}^3\) portions of B using methyl orange as indicator. Repeat the titration to obtain consistent titres. Tabulate your results and calculate the average volume of acid used.

9b) From your results and information provided above, calculate the;

(i) concentration of A in \(\mathrm{mol\,dm}^{-3}\)

(ii) concentration of B in \(\mathrm{mol\,dm}^{-3}\)

(iii) solubility of \(\mathrm{Na}_2\mathrm{CO}_3\) in \(\mathrm{mol\,dm}^{-3}\)

(iv) volume of \(\mathrm{CO}_2\) that would be liberated from \(1\text{ dm}^3\) of B if the titration were carried out at s.t.p.

The equation for the reaction is \(\mathrm{Na}_2\mathrm{CO}_{3(aq)} + 2\mathrm{HCl}_{(aq)} \to 2\mathrm{NaCl}_{(aq)} + \mathrm{H}_2\mathrm{O}_{(l)} + \mathrm{CO}_{2(g)}\)

[H = 1; C = 12; O = 16; Na = 23; Cl = 35.5; Molar volume of gas at s.t.p = \(22.4\text{ dm}^3\)]

Credit will be given for strict adherence to the instructions, for observations precisely recorded, and for accurate inferences. All tests, Observations, and inferences must be clearly entered in your answer book, in ink, at the time they are made.

C is a mixture of two inorganic salts. Carry out the following exercises on C. Record your observations and identify any gas(es) evolved. State the conclusion you draw from the result of each test.

(a) Put all of C in a test tube and add about \(10\ \text{cm}^3\) of distilled water. Stir, filter, and keep the filtrate and the residue.

(b) Put the residue into a test tube and add about \(5\ \text{cm}^3\) of dilute HCl. Shake to dissolve

(i) To about \(2\ \text{cm}^3\) of the solution, add \(\mathrm{NaOH_{(aq)}}\) in drops and then in excess

(ii) To another \(2\ \text{cm}^3\) portion of the solution, add \(\mathrm{NH_{3(aq)}}\) in drops and then in excess.

(c) To about \(2\ \text{cm}^3\) portion of the filtrate, add few drops of dilute \(\mathrm{HNO_3}\), and then \(\mathrm{AgNO_{3(aq)}}\) a followed by aqueous \(\mathrm{NH_3}\) in excess.