Question

2. G is an inorganic salt. Carry out the following exercises on G. Record your observations and identify any gas(es) evolved. State the conclusions you draw from the results of each test.
(a) Dissolve all of G in 10 cm3 of distilled water in a boiling tube.
(b) (i) Test the resulting solution with litmus paper.
 (ii) To about 2 cm3 portion of the solution in a test tube, add NaOH(aq); then warm the resulting mixture gently.
 (iii) To another 2 cm3 portion of the solution, add dilute HNO3.
 (iv) To 2 cm3 portion of the solution, add BaCl2(aq) followed by excess dilute HNO3.

Accepted Answer

G + distilled water → a colourless solution is obtained.

(b)(i) Solution of G + litmus paper → red litmus turns blue → solution of G is alkaline/basic.
(ii) Solution of G + NaOH(aq), then warmed → no immediate visible precipitate; on warming, a colourless gas is evolved with a pungent/choking/irritating smell → the gas turns red litmus paper blue and forms dense white fumes with concentrated HCl → the gas is ammonia (NH3) → NH4⁺ is present.
(iii) Solution of G + dilute HNO3 → effervescence, a colourless gas is evolved → the gas turns limewater milky → the gas is CO2, indicating CO3²⁻ or HCO3⁻ is present.
(iv) Solution of G + BaCl2(aq) + excess dilute HNO3 → a white (chalky) precipitate forms initially, then dissolves with rapid effervescence on adding the acid → this rules out SO4²⁻ (which would not dissolve) and SO3²⁻, confirming CO3²⁻ is present.

WAEC Chemistry 2023 Theory — Question 13

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