All your burette readings (initials and final) as well as the size of your pipette must be recorded but no account of experimental procedure is required. All calculations must be done in your answer booklet.
C is a mixture of two inorganic compounds. Carry out the following exercises on C. Record your observations and identify any gas(es) evolved. State the conclusions you draw from the result of each test.
(a) Put all of C in a boiling tube and add about 10 cm\(^3\) of distilled water. Shake thoroughly and filter. Keep both the residue and the filtrate.
(b)(i) To about 2 cm\(^3\) of the filtrate add a few drops of Silver trioxoitrate (V) followed by dilute HNO\(_{3}\)
(ii) Add excess NH\(_3\) solution to the resulting mixture in (b)(i).
(C)(i) Put the residue in a test tube, add about 2 cm\(^3\) of dilute HCl and shake.
(ii) Add NH\(_3\) Solution in drops to the mixture from (c)(i) and then in excess.
Explanation
| TEST | OBSERVATION | INFERENCE |
| (a) C + distilled water and filter |
C dissolved partially forming a green residue with colorless filtrate |
Fe\(^2+\) or Cu\(^{2+}\) salt is present |
| (b)(i) 2cm\(^3\) of filtrate + AgNO\(_{3(aq)}\) + HNO\(_{3(aq)}\) |
White precipitate formed Precipitate insoluble or No visible change |
Cl\(^{-}\), CO\(_3^{2-}\) or SO\(_3^{2-}\), S\(^{2-}\) Cl\(^-\) is present |
| (ii) Resulting mixture in (b)(i) + excess NH\(_{3(aq)}\) | Precipitate dissolves or soluble | Cu\(^{-}\) is present |
| (c)(i) Residue + dil HCl |
The residue dissolved to form a blue solution effervescence (bubbling) occurs. Colourlessness, odourless gas evolved that turned blue litmus paper red and turned lime water milky |
Cu\(^{2+}\) is present CO\(_{2(g)}\) from CO\(_3^{2-}\) |
| (ii) Portion of mixture of (c)(i) + NH\(_{3(aq)}\) in drops then in excess | Light (Pale) blue precipitate formed in drop of NH\(_{3(aq)}\) to form a deep blue solution | CO\(^{2+}\) is confirmed |