Further analysis and quantitive chemistry

Question 1

A test can be used to identify sodium ions and potassium ions. Describe the test. Give the result of the test for sodium ions and for potassium ions. [3]

Answer 1

• place sample in flame
• sodium: yellow (flame)
• potassium: lilac (flame)

Question 2

It is difficult to identify potassium ions when sodium ions are present. Suggest why. [1]

Answer 2

(lilac) colour (of potassium) obscured by (yellow) colour of sodium.

Question 3

Describe how the student would test a solution of the low sodium salt for chloride ions. Give the result of the test. [3]

Answer 3

• acidify (with nitric acid)
• add silver nitrate (solution)
• white precipitate should be formed

Question 4

Describe how the student could confirm that the low sodium salt contains magnesium ions and not aluminium ions. [2]

Answer 4

• add excess (sodium hydroxide)

- aluminium will redissolve

Question 5

Describe a test the student could do to confirm that the low sodium salt does not contain calcium ions.

Answer 5

• place a sample in flame

- flame does not go red

Question 6

Complete Table. [2]
Chemical                     Colour produced in firework
- barium chloride        - green
- \_\_\_\_ carbonate       - crimson
- sodium nitrate          - \_\_\_\_
- calcium sulfate         - red

Answer 6

• lithium

- yellow

Question 7

Describe a test to show that barium chloride solution contains chloride ions. Give the result of the test. [2]

Answer 7

• add silver nitrate (solution)

- white precipitate should be formed