Chemical tests

Question 1

How do you carry out a flame test?

Answer 1

Clean a platinum or nichrome wire (dip in dilute HCl then hold in flame), dip it into the sample, and place it in a Bunsen flame to observe the colour produced.

Question 2

What colour does Li⁺ burn?

Answer 2

Red flame

Question 3

What colour does Na⁺ burn?

Answer 3

Yellow flame

Question 4

What colour does K⁺ burn?

Answer 4

Lilac flame

Question 5

What colour does Ca²⁺ burn?

Answer 5

Orange-red flame

Question 6

What colour does Cu²⁺ burn?

Answer 6

Blue-Green flame

Question 7

Test for NH₄⁺

Answer 7

Add sodium hydroxide solution and heat gently. Ammonia gas (NH₃) is evolved, which turns red litmus paper blue

Question 8

Test for Cu²⁺

Answer 8

Add sodium hydroxide solution. A blue precipitate of copper(II) hydroxide (Cu(OH)₂) forms

Question 9

Test for Fe²⁺

Answer 9

Add sodium hydroxide solution. A green precipitate of iron(II) hydroxide (Fe(OH)₂) forms

Question 10

Test for Fe³⁺

Answer 10

Add sodium hydroxide solution. A brown precipitate of iron(III) hydroxide (Fe(OH)₃) forms

Question 11

Test for Cl⁻

Answer 11

Add acidified silver nitrate solution. A white precipitate of silver chloride (AgCl) forms

Question 12

Test for Br⁻

Answer 12

Add acidified silver nitrate solution. A cream precipitate of silver bromide (AgBr) forms

Question 13

Test for I⁻

Answer 13

Add acidified silver nitrate solution. A yellow precipitate of silver iodide (AgI) forms