TEST OF PRACTICAL KNOWLEDGE QUESTION
Credit will be given for strict adherence to the instructions, for observations precisely record 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.
C is a mixture of two salts. Carry out the following exercises on C. Record your observations and identify any gas(es) evolved. State the conclusion drawn from the result of each fest
(a) Put all of C into a boiling tube and add about 5cm\(^3\) of distilled water. Stir thoroughly and filter. Keep both the residue and the filtrate.
(b) To about 2 cm\(^3\) of the filtrate, add few drops of Pb(NO\(_3\))\(_{(aq)}\). Boil the mixture and then allow to cool.
(c)(i) Put the residue in a test tube and add dilute HNO\(_{3}\). Shake the mixture and divide the solution into two portions
(ii) to the first portion from (c)(i), add NaOH\(_{(aq)}\) in drops acid then in excess.
(iii) To the second portion from (c)(ii), add aqueous ammonia in drops and then in excess
C is a mixture of two salts. The tests, observations and inferences are recorded below.
| Test | Observation | Inference |
|---|
| (a) All of C + about 5 cm3 of distilled water, stirred thoroughly and filtered | C partly dissolved; a colourless filtrate was obtained with a white residue left on the filter paper | C contains a soluble salt (in the filtrate) and an insoluble salt (the residue) |
| (b) About 2 cm3 of the filtrate + a few drops of Pb(NO3)2, boiled then cooled | A white precipitate formed; it dissolved on boiling and reappeared as needle-like crystals on cooling | Cl- confirmed (PbCl2 is soluble in hot water and recrystallises on cooling) |
| (c)(i) Residue + dilute HNO3 | Effervescence occurred; a colourless, odourless gas that turned lime water milky was evolved | CO2 evolved from CO32-; the residue is a trioxocarbonate(IV) |
| (c)(ii) Solution from (c)(i) + NaOH(aq) in drops then in excess | A white gelatinous precipitate formed which dissolved in excess NaOH | Zn2+ or Al3+ present |
| (c)(iii) Solution from (c)(i) + aqueous ammonia in drops then in excess | A white gelatinous precipitate formed which dissolved in excess ammonia | Zn2+ confirmed |
Ionic equations: \(Pb^{2+} + 2Cl^- \rightarrow PbCl_2\) and \(CO_3^{2-} + 2H^+ \rightarrow H_2O + CO_2\).
C is a mixture of two salts. The tests, observations and inferences are recorded below.
| Test | Observation | Inference |
|---|
| (a) All of C + about 5 cm3 of distilled water, stirred thoroughly and filtered | C partly dissolved; a colourless filtrate was obtained with a white residue left on the filter paper | C contains a soluble salt (in the filtrate) and an insoluble salt (the residue) |
| (b) About 2 cm3 of the filtrate + a few drops of Pb(NO3)2, boiled then cooled | A white precipitate formed; it dissolved on boiling and reappeared as needle-like crystals on cooling | Cl- confirmed (PbCl2 is soluble in hot water and recrystallises on cooling) |
| (c)(i) Residue + dilute HNO3 | Effervescence occurred; a colourless, odourless gas that turned lime water milky was evolved | CO2 evolved from CO32-; the residue is a trioxocarbonate(IV) |
| (c)(ii) Solution from (c)(i) + NaOH(aq) in drops then in excess | A white gelatinous precipitate formed which dissolved in excess NaOH | Zn2+ or Al3+ present |
| (c)(iii) Solution from (c)(i) + aqueous ammonia in drops then in excess | A white gelatinous precipitate formed which dissolved in excess ammonia | Zn2+ confirmed |
Ionic equations: \(Pb^{2+} + 2Cl^- \rightarrow PbCl_2\) and \(CO_3^{2-} + 2H^+ \rightarrow H_2O + CO_2\).
