8.3 Identification of ions by chemical and spectroscopic means

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Question 2

A student investigated an aqueous solution of an unknown salt. The student identified that the salt solution contained only calcium ions and chloride ions.

Describe a test to identify calcium ions. Give the result of the test.

[2]

Describe a test to identify chloride ions. Give the result of the test.

[2]

The student determined the concentration of calcium chloride in the salt solution using the following method:

Weigh an empty evaporating basin.
Add $cm325.0\text{ cm}^3$ of the salt solution into the evaporating basin.
Heat the evaporating basin and contents.
Weigh the evaporating basin and contents.
Repeat steps 3 to 4 until there is no further change in mass.
Repeat steps 1 to 5 three more times.

Why did the student heat the evaporating basin and contents until the mass did not change?

[1]

How did the student calculate the mass of solid calcium chloride remaining after steps 1 to 5?

Select one option:

Option A: $basin\text{Mass of } 25.0\text{ cm}^3\text{ of salt solution} + \text{mass of empty evaporating basin}$
Option B: $basin\text{Mass of } 25.0\text{ cm}^3\text{ of salt solution} - \text{mass of empty evaporating basin}$
Option C: $basin\text{Mass of evaporating basin and dry contents} + \text{mass of empty evaporating basin}$
Option D: $basin\text{Mass of evaporating basin and dry contents} - \text{mass of empty evaporating basin}$

[1]

The student calculated the concentration of calcium chloride in the salt solution. Table 1 shows the 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 ( $g/dm3\text{g/dm}^3$ )
34.8	35.4	34.6	35.2

The percentage by mass of calcium ions in calcium chloride is $36.1%36.1\%$ .

Calculate the mean concentration of calcium ions in the salt solution.

[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

)

34.8

35.4

34.6

35.2

8.3 Identification of ions by chemical and spectroscopic means

Question 2

Markscheme

8.3 Identification of ions by chemical and spectroscopic means

Question 2

Markscheme

8.3 Identification of ions by chemical and spectroscopic means

Question 2

8.3 Identification of ions by chemical and spectroscopic means Questions

8.3 Identification of ions by chemical and spectroscopic means

Question 2

8.3 Identification of ions by chemical and spectroscopic means Questions