Credit will be given for strict adherence to instructions, for observations precisely recorded, and for accurate inferences. All tests, observations, and in...
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 an inorganic salt. D is an organic compound. Carry out the following exercises on C and D. Record your observations and identify any gases evolved. State the conclusion you draw from the result of each test.
(a) (i) Put C in a test tube and add about 10 cm\(^3\) of distilled water. Stir well.
(ii) Divide the resulting solution into two portions. To the first portion add sodium hydroxide solution in drops and then in excess.
(iii) To the second portion add dilute trioxonitrate (V) acid. Then add silver trioxonitrate (V) solution followed by aqueous ammonia in excess. tube and odd about 2- 5 cm\(^3\) of 'Xn'.
(ii) Identify the functional group present in D.
Answer Details
Identification: Specimen C is calcium chloride, \(\text{CaCl}_2\) (supplying \(\text{Ca}^{2+}\) and \(\text{Cl}^{-}\) ions), and specimen D is a carboxylic (alkanoic) acid carrying the carboxyl functional group, \(-\text{COOH}\).
| Test | Observation | Inference |
|---|---|---|
| (a)(i) C put in a test tube; about \(10\ \text{cm}^3\) of distilled water added and stirred well. | C dissolves completely to give a colourless solution. | C is a soluble salt. |
| (a)(ii) First portion + sodium hydroxide solution, \(\text{NaOH}_{(aq)}\), in drops and then in excess. | A white precipitate forms which is insoluble in excess \(\text{NaOH}\). | \(\text{Ca}^{2+}\) is present. \(\text{Ca}^{2+}_{(aq)} + 2\text{OH}^{-}_{(aq)} \rightarrow \text{Ca(OH)}_2{}_{(s)}\) |
| (a)(iii) Second portion + dilute trioxonitrate(V) acid, \(\text{HNO}_{3(aq)}\), then silver trioxonitrate(V) solution, \(\text{AgNO}_{3(aq)}\), then aqueous ammonia, \(\text{NH}_{3(aq)}\), in excess. | No reaction with the acid; on adding \(\text{AgNO}_{3(aq)}\) a white precipitate forms, which dissolves in excess aqueous ammonia to give a colourless solution. | \(\text{Cl}^{-}\) is present; \(\text{Cl}^{-}\) confirmed. \(\text{Ag}^{+}_{(aq)} + \text{Cl}^{-}_{(aq)} \rightarrow \text{AgCl}_{(s)}\) Together with (ii), C is calcium chloride. |
| (b) D + sodium hydrogentrioxocarbonate(IV) solution, \(\text{NaHCO}_{3(aq)}\). | Brisk effervescence of a colourless gas which turns lime water milky. | The gas is carbon(IV) oxide, \(\text{CO}_2\); D is an organic (alkanoic) acid. The functional group present is the carboxyl group, \(-\text{COOH}\). \(\text{RCOOH} + \text{NaHCO}_3 \rightarrow \text{RCOONa} + \text{H}_2\text{O} + \text{CO}_2\) |
Conclusion: C is calcium chloride, containing the \(\text{Ca}^{2+}\) cation and the \(\text{Cl}^{-}\) anion. D is a carboxylic (alkanoic) acid, and the functional group present in D is the carboxyl group, \(-\text{COOH}\).
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