8.3 Identification of ions by chemical and spectroscopic means

A student investigated an aqueous solution of a salt. The student identified that the salt solution contained only lithium ions and iodide ions.

Describe a test to identify lithium ions in the solution. State the expected observation.

[2]

Describe a test to identify iodide ions in the solution. State the expected observation.

[2]

The student determined the concentration of lithium iodide in the salt solution using the following method:

Explain why the student heated the evaporating basin and its contents until a constant mass was achieved.

[1]

How did the student determine the mass of the dry lithium iodide remaining after completing step 5?

Select one option:

Option A: $basin\text{Mass of } 50.0\text{ cm}^3\text{ of salt solution} - \text{mass of empty evaporating basin}$
Option B: $basin\text{Mass of evaporating basin and dry contents} - \text{mass of empty evaporating basin}$
Option C: $contents\text{Mass of empty evaporating basin} - \text{mass of evaporating basin and dry contents}$
Option D: $basin\text{Mass of evaporating basin and dry contents} + \text{mass of empty evaporating basin}$

[1]

The student calculated the concentration of lithium iodide in the salt solution for each trial. Table 1 shows these results:

Trial 1 ( $g/dm3\text{g/dm}^3$ )	Trial 2 ( $g/dm3\text{g/dm}^3$ )	Trial 3 ( $g/dm3\text{g/dm}^3$ )	Trial 4 ( $g/dm3\text{g/dm}^3$ )
62.4	61.8	63.1	61.5

The percentage by mass of lithium ions in lithium iodide is $5.16%5.16\%$ .

Calculate the mean concentration of lithium ions in the salt solution. Give your answer to 3 significant figures.

[3]

Trial 1 (

g/dm3\text{g/dm}^3

)

Trial 2 (

g/dm3\text{g/dm}^3

)

Trial 3 (

g/dm3\text{g/dm}^3

)

Trial 4 (

g/dm3\text{g/dm}^3

)

62.4

61.8

63.1

61.5

8.3 Identification of ions by chemical and spectroscopic means

8.3 Identification of ions by chemical and spectroscopic means Questions