Sodium Hydroxide Tests for Cations

Question 1

How would you test for cations?

(not flame test)

Answer 1

1. Add dilute (hydrochloric/nitric) acid
2. Add sodium hydroxide

Question 2

Colour of precipitate for copper (II) ion (Cu²⁺) reaction with sodium hydroxide (NaSO₄)

Answer 2

Blue

Question 3

Colour of precipitate for iron (II) ion (Fe²⁺) reaction with sodium hydroxide (NaSO₄)

Answer 3

Green

Question 4

Colour of precipitate for iron (III) ion (Fe³⁺) reaction with sodium hydroxide (NaSO₄)

Answer 4

Reddish-brown

Question 5

How would you test for ammonium ions (NH₄⁺)?

Answer 5

1. Add sodium hydroxide to the substance in a test tube.
2. Heat gently over a Bunsen burner with damp red litmus paper over the test tube.
3. If ammonium is present, ammonia gas is given off and litmus paper turns blue.

Question 6

Ionic equation for reaction using ammonium and sodium hydroxide

Answer 6

NH₄⁺ + OH^- —> NH₃ + H₂O