Fig. 1 shows a student testing water from a borehole near a road-salt store. The student first adds dilute nitric acid, then silver nitrate solution, to a s...
Question 1 Report
Fig. 1 shows a student testing water from a borehole near a road-salt store. The student first adds dilute nitric acid, then silver nitrate solution, to a sample in a test tube.
Table 1 shows the mass of solid collected after the same volume of silver nitrate solution was used with three water samples.
| sample | mass of solid / g |
|---|---|
| borehole water | 0.42 |
| rain water | 0.00 |
| salt-store drain | 0.86 |
(a) Complete the observation for the borehole water: a ______ precipitate forms. [1]
(b) Name the ion identified by this test. [1]
(c) Use Table 1 to give the sample with the greatest concentration of this ion. [1]
(d) Suggest why nitric acid is added before silver nitrate solution. [1]
(e) Give the formula of the precipitate made when chloride ions react with silver ions. [2]
Answer Details
- (a) A white precipitate forms. [1]
- (b) This test identifies chloride ions, \(\text{Cl}^-\). [1]
- (c) The salt-store drain gives the greatest mass of precipitate, so it has the greatest concentration of chloride ions: salt-store drain. [1]
- (d) Nitric acid removes carbonate ions, preventing carbonates from forming a precipitate with silver ions and giving a false positive. [1]
- (e) Silver ions and chloride ions combine in a 1:1 ratio: \(\text{AgCl}\). [2]
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