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 mıxture of two salts, containing one cation and two anions. 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 beaker and add about 10 cm\(^3\) of distilled water. Stir well and filter. Keep the filtrate and the residue.
(b) To about 2 cm\(^3\) of the filtrate, add few drops of AgNO\(_{(aq)}\), followed by HNO\(_{3(g)}\). Add excess NH\(_{3(aq)}\) to the resulting mixture.
(c)(i) Put all of the residue into a clean test tube and add about 5 cm of HNO\(_{3(aq)}\)
(ii) To about 2 cm\(^3\) of the solution from 2(c)(i), add NaOH\(_{(aq)}\) in drops and then in excess
(iii) To another 2 cm\(^3\) of the solution from 2(c)(i), add NH\(_{3(aq)}\) in drops and then in excess.
Explanation
| Test | Observation | Inference | |
| (a) | C\(_{(s)}\) + distilled water + filter | Party dissolved/soluble colourless filtrate obtained, water residue | C contains soluble and insoluble salts |
| (b) |
Filtrate C + AgNO\(_{3(aq)}\) + HNO\(_{3(aq)}\) + NH\(_{3(aq)}\) |
White precipitate Precipitate insoluble Precipitate soluble/dissolved |
Cl\(^{-}\) or CO\(_3^{2-}\) or SO\(_3^{2-}\) Cl\(^-\) Cl\(^-\) present |
| (c)(i) | Residue + HNO\(_{3(aq)}\) |
Effervescence, colourless, Odourless gas evolved Gas turned lime water milky |
CO\(_2\) gas from CO\(_3^{2-}\) evolved |
| (ii) |
Solution from C(i) + NaOH\(_{3(aq)}\) drops Then in excess |
White gelatinous precipitate Precipitate dissolved/soluble |
Zn\(^{2+}\) or Al\(^{3+}\) present |
| (iii) |
Solution from C(i) + NH\(_{3(aq)}\) drops Then in excess |
White gelatinous precipitate Precipitate dissolved/soluble |
Zn\(^{2+}\) or Al\(^{3+}\) present Zn\(^{2+}\) present |