Tests for positive ions (cations)

Question 1

What’s the effect of

Adding sodium hydroxide to a solution with ammonium (NH₄⁺)

Answer 1

Ammonia produced on warming (test with damp red litmus paper)

Question 2

What’s the effect of

Adding sodium hydroxide to a solution with copper(II) (Cu²⁺)

Answer 2

Light blue gelatinous precipitate of copper hydroxide; insoluble in excess sodium hydroxide

Question 3

What’s the effect of

Adding ammonia solution to a solution with copper(II) (Cu²⁺)

Answer 3

Light blue gelatinous precipitate; dissolves in excess ammonia, giving a deep blue solution

Question 4

What’s the effect of

Adding sodium hydroxide to a solution with iron(II) (Fe²⁺)

Answer 4

Green gelatinous precipitate of iron(II) hydroxide; insoluble in excess

Question 5

What’s the effect of

Adding ammonia solution to a solution with iron(II) (Fe²⁺)

Answer 5

Green gelatinous precipitate; insoluble in excess

Question 6

What’s the effect of

Adding sodium hydroxide to a solution with iron(III) (Fe³⁺)

Answer 6

Rust-brown gelatinous precipitate of iron(III) hydroxide; insoluble in excess

Question 7

What’s the effect of

Adding ammonia solution to a solution with iron(III) (Fe³⁺)

Answer 7

Rust-brown gelatinous precipitate; insoluble in excess

Question 8

What’s the effect of

Adding sodium hydroxide to a solution with calcium (Ca²⁺)

Answer 8

White precipitate of calcium hydroxide; insoluble in excess

Question 9

What’s the effect of

Adding ammonia solution to a solution with calcium (Ca²⁺)

Answer 9

No precipitate (or only a very slight precipitate)

Question 10

What’s the effect of

Adding sodium hydroxide to a solution with zinc (Zn²⁺)

Answer 10

White precipitate of zinc hydroxide; soluble in excess, giving a colourless solution

Question 11

What’s the effect of

Adding ammonia solution to a solution with zinc (Zn²⁺)

Answer 11

White precipitate; soluble in excess

Question 12

What’s the effect of

Adding sodium hydroxide to a solution with aluminium (Al³⁺)

Answer 12

White precipitate of aluminium hydroxide; soluble in excess, giving a colourless solution

Question 13

What’s the effect of

Adding ammonia solution to a solution with aluminium (Al³⁺)

Answer 13

White precipitate; insoluble in excess

Question 14

What’s the effect of

Adding sodium hydroxide to a solution with magnesium (Mg²⁺)

Answer 14

White precipitate of magnesium hydroxide; insoluble in excess

Question 15

What’s the effect of

Adding ammonia solution to a solution with magnesium (Mg²⁺)

Answer 15

White precipitate; insoluble in excess