Credit will be given for strict adherence to instructions, for observations precisely recorded and for accurate inferences. All tests observations and infer...
Question 1 Report
Credit will be given for strict adherence to 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.
C is a mixture of two simple salts. Carry out the following exercises on C. Record your observations and identify any gases evolved. Sate the conclusion you draw from the result of each test.
(a) Put all of C into a beaker of boiling tube and add about \(10\text{cm}^3\) of distilled water. Stir well and filter. Keep the residue and keep the residue and the filtrate. Test the filtrate with litmus
(b) Add about \(1\text{ cm}^3\) of dilute hydrochloric acid to the residue in a test tube and warm gently Divide the reaction mixture into two portions
(c)(i) To the first portion from (b) add saturated sodiuim trioxocarbonate (V) solution in excess
(d) To bout \(2\text{cm}^2\) of the filtrate from (a) add a few drops of barium chloride solution followed by excess dilute hydrochloric acid
Answer Details
Tests on Specimen C
| Test | Observation | Inference / conclusion |
|---|---|---|
| (a) Add water to C, stir and filter. Test the filtrate with litmus paper. | Part of C dissolves, leaving a green insoluble residue. A colourless filtrate is obtained. The filtrate has no effect on red or blue litmus paper. | C contains a soluble salt and an insoluble salt. The soluble salt gives a neutral solution. |
| (b) Add dilute hydrochloric acid to the residue and warm gently. | Effervescence occurs. A colourless, odourless gas is evolved; it turns limewater milky. The green residue dissolves to give a blue-green solution. | The gas is carbon(IV) oxide, \(\mathrm{CO_2}\); hence \(\mathrm{CO_3^{2-}}\) is present. The blue-green solution indicates \(\mathrm{Cu^{2+}}\). |
| (c)(i) Add saturated sodium trioxocarbonate(V) solution in excess to one portion from (b). | Effervescence occurs at first. A blue-green precipitate is then formed and remains insoluble in excess sodium trioxocarbonate(V) solution. | The initial effervescence is due to reaction of excess hydrochloric acid with carbonate ions. The blue-green precipitate confirms \(\mathrm{Cu^{2+}}\) ions. |
| (d) Add barium chloride solution to the filtrate from (a), followed by excess dilute hydrochloric acid. | A white precipitate is formed. The precipitate does not dissolve in excess dilute hydrochloric acid. | Tetraoxosulphate(VI) ions, \(\mathrm{SO_4^{2-}}\), are present. |
Equations:
\[\mathrm{CuCO_3(s)+2HCl(aq)\rightarrow CuCl_2(aq)+H_2O(l)+CO_2(g)}\]
\[\mathrm{Ba^{2+}(aq)+SO_4^{2-}(aq)\rightarrow BaSO_4(s)}\]
Final conclusion: C is a mixture of insoluble copper(II) trioxocarbonate(IV), \(\mathrm{CuCO_3}\), and a soluble tetraoxosulphate(VI), represented by sodium tetraoxosulphate(VI), \(\mathrm{Na_2SO_4}\).
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