8. Chemical analysis (required practical 7 - identifying ions)

Question 1

What is the practical investigating?

Answer 1

using chemical tests to identify the ions in unknown compounds

Question 2

What are the steps for a flame test?

Answer 2

1. Clean the nichrome wire loop with HCL
2. Dip into the sample salt
3. Place into the roaring blue flame
4. Use the colour of the flame to identify the metal or compound

Question 3

What ion does a crimson flame correspond to?

Answer 3

lithium ion

Question 4

What ion does a yellow flame correspond to?

Answer 4

sodium ion

Question 5

What ion does a lilac flame correspond to?

Answer 5

potassium ion

Question 6

What ion does a green flame correspond to?

Answer 6

copper ion

Question 7

What ion does a orange-red (brick red) flame correspond to?

Answer 7

calcium ion

Question 8

Why might the colour of the flame sometimes be masked?

Answer 8

as a compound may contain a mixture of different ions

Question 9

What are the different ways cations (metal ions) can be identified?

Answer 9

• flame tests
• testing with sodium hydroxide

Question 10

How can cations be tested for in sodium hydroxide?

Answer 10

1. Add sodium hydroxide to an unknown solution with white metal compounds
2. It may form a white precipitate, which tells us that the metal ion can either be aluminium, calcium or magnesium
3. If you keep adding excess sodium hydroxide to the solution and the white precipitate dissolves again, it is aluminium