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 booklet.
C and D are inorganic salts. Carry out the following exercises on them. 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 test tube and add about 5 cm of distilled water. Shake thoroughly and test the resulting solution with Litmus paper. Divide the solution into three portions.
(i) To the first portion, add NaOH\(_{(aq)}\) in drops, then in excess.
(ii) To the second portion. add NH\(_{3(aq)}\) in drops. then in excess.
(iii) To the third portion. add AgNO\(_{3 (aq)}\) followed by HCl\(_{(aq)}\)
(b)(i) Put all of D in a test tube and add about 5 cm\(^3\) of distilled water. Shakę thoroughly and feel the test tube.
(ii) To about 2 cm\(^3\) of the solution, add HCl\(_{(aq)}\)
Explanation
| TEST | OBSERVATION | INTERFERENCE |
|
(a) Sample C + distilled water + shaking Resulting solution + litmus paper |
Sample C dissolved to form a blue/greenish solution Solution turns blue litmus paper red |
Solution is acidic |
|
(I) 1st portion + NaOH\(_{(aq)}\) in drops Then in excess |
Blue precipitate formed Precipitate insoluble in excess |
Cu\(^{2+}\) is present |
|
(ii) 2nd portion NH\(_4\)OH\(_{(aq)}\) in drops Then in excess |
Light blue precipitate formed Precipitate dissolve in excess to form a deep blue solution |
Cu\(^{2+}\) is confirmed |
| (iii) 3rd portion + AgNO\(_{3(aq)}\)+ NCl\(_{(aq)}\) |
White precipitate formed Precipitate insoluble |
Cl\(^{-1}\) or CO\(_{3^{2-}}\) or S\(^{2-}\) or SO\(_3^2\) Cl\(^{2-}\) is present |
|
(b)(i) Sample D + distilled water touching or feeling the test tubes |
Sample D dissolved to form a colourless solution Test tube feels cold on touching |
Dissolution is endothermic |
| (ii) D\(_{(aq)}\) = HCl\(_{(aq)}\) |
Effervescence (bubbling) occurs, a colourless, odourless gad evolved Gas turned lime water milky |
CO\(_{2(g)}\) from CO\(_{3^{2-}}\) or HCO\(_3^-\) |