You are provided with two aqueous solutions labelled C and D. Carry out the following exercises on them. Record your observations and identify any gases evolved. State the condition you draw from the result of each test.
(a)(i) Mix C and D in a beaker thoroughly.
(ii) Filter the mixture. Keep both the residue and the filtrate.
(b)(i) To about 5cm\(^3\) of the filtrate, add barium chloride solution, followed by excess dilute hydrochloric acid in a boiling tube. Divide the resulting solution into two portions.
(c)(i) To the first portion of the solution from (b)(ii) above, add sodium hydroxide solution in excess.
(ii) To the second portion of the solution from (b)(ii) above, add aqueous ammonia in drops until it is in excess.
Explanation
| Test | Observation | Influence |
| (a)(i) C + D | Blue precipitate formed | Cu\(^{2+}\) is probably present |
| (ii) Mixed filtered | Colourless filtrate, Blue residue | Cu\(^{2+}\) probably present |
| (b)(i) Filtrate + BaCl\(_{2(aq)}\) + dil. HCl in excess |
White precipitate formed. Precipitate insoluble |
SO\(_4^{2-}\) or SO\(_3^{2-}\) or CO\(_3^{2-}\) present |
| (ii) Residue + dil. HCl |
Effervescence gas evolved. The gas was odourless and turned lime water milky. Residue dissolved to give a pale blue solution |
SO\(_4^{2-}\) present CO\(_4^{2-}\) from CO\(_3^{2-}\) Cu\(^{2+}\) probably present |
| (c)(i) Soln. from (b)(i) + excess NaOH\(_{(aq)}\) | light blue precipitate insoluble in excess | Cu\(^{2+}\) present |
| (ii) Soln. from (b)(ii) + NH\(_{3(aq)}\) in drops until in excess |
Pale blue precipitate soluble in excess NH\(_{3(aq)}\) to give a deep blue solution |
Cu\(^{2+}\) confirmed |