4.6.2 Cation tests

Question 1

What are cations?

Answer 1

Positive ions.

Question 2

What flame should be used in a flame test?

Answer 2

A non-luminous flame.

Question 3

How do you conduct a flame test?

Answer 3

• Dip a piece of nichrome/platinum wire into HCl, this cleans the wire.
• Dip the wire into a sample.
• Place the tip of the wire into a non-luminous Bunsen burner flame.

Question 4

What is the test for Li+?

Answer 4

Red flame test.

Question 5

What is the test for Na+?

Answer 5

Yellow flame test.

Question 6

What’s the test for K+?

Answer 6

Lilac flame test.

Question 7

What’s the test for Ca2+?

Answer 7

Orange-red flame test.

Question 8

What’s the test for Cu2+? (flame test)

Answer 8

Blue-green flame test.

Question 9

How do you conduct an NaOH test?

Answer 9

• Dissolve the sample in water.
• Add a few drops of NaOH.

Question 10

What’s the test for Cu2+? (NaOH) And what ppt is formed?

Answer 10

Blue NaOH test, ppt formed is Cu(OH)2.

Question 11

What’s the test for Fe2+? And what’s the ppt formed?

Answer 11

Green NaOH test, ppt formed is Fe(OH)2.

Question 12

What’s the test for Fe3+? And what’s the ppt formed?

Answer 12

Brown NaOH test, ppt formed is Fe(OH)3.

Question 13

What’s the test for ammonium (NH4^+)

Answer 13

• Dissolve the sample in water.
• Add some NaOH and warm it.
• Test the gas evolved with damp red litmus paper. It should turn blue.