Credit will be given for strict adherence to the instructions, for observations precisely recorded, and for accurate inferences. All tests, Observations, and inferences must be clearly entered in your answer book, in ink, at the time they are made. Carry out the following exercises on sample C.
Record your observations and identify any gases evolved
(a) Put all of C into a test tube and add about 5cm\(^3\) of water. Shake the mixture and filter. Keep both the residue and the filtrate
(b) Divide the filtrate into two portions;
(i) To the first portion, add a few drops of dilute trioxonitrate (V) acid followed by about 1cm\(^3\) of silver trioxonitrate (V) solution
(ii) Add excess aqueous ammonia to the mixture in (i) above
(iii) To the second portion, add about 2cm\(^3\) of dilute sodium hydroxide solution and warm gently
(c) Add about 2cm\(^3\) of dilute hydrochloric acid to the residue from (a) above and warm gently. Filter if necessary and divide the resulting solutio into two portions.
(i) To the first portion add dilute sodium hydroxide solution in drops until it is in excess
(ii) To the second portion, add aqueus ammonia in drops until it is in excess.
| Test | Observation | Inference |
|
(a)(i) C + water and filtered |
part of sample dissolves colourless filtrate salt |
C is a mixtue of soluble salt |
|
(b)(i) Filtrate + dil. HNO\(_3\) + ANO\(_3\) (ii) The mixture from (b)(i) above + excess aqeuous NH\(_3\) |
White ppt. ppt. dissolves |
Cl present Cl confirmed |
| (iii) Filtrte + NaOH\(_{(aq)}\) and warmed | colourless gas evolved with characteristic choking smell; turns limit blue and forms white fumes with conc. HCl acid stopper/vapour |
Gas is NH\(_3\) NH\(_4^+\) present |
| (c)Residue from (a) + dil. HCl | Residue dissolves liberating a colourless gas which turns lime water milky |
the gas is CO\(_2\) CO\(_3^{2-}\) present |
| (c)(i) Solution from (C) + NaOH\(_{(aq)}\) | white ppt; soluble in excess NaOH\(_{(aq)}\) | Zn\(^{2+}\) or Pb\(^{2+}\) present |
| (ii) Solution from C + NH\(_{3(aq)}\) | white ppt. solution in excess NH\(_{3(aq)}\) | Zn\(^{2+}\) confirmed |
From the results, C is a mixture of ZnCO\(_3\) and NH\(_4\)Cl
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