Precipitation Reactions

Question 1

What happens when Cu2+ is reacted with NaOH?

Answer 1

The blue solution reacts to form the blue precipitate Cu(OH)2

Question 2

What happens when Fe2+ reacts with NaOH and is then left standing?

Answer 2

1. Pale green solution reacts to form a green precipitate
2. Oxidises when left standing to form an orange/brown precipitate

Question 3

What happens when Fe3+ reacts with NaOH?

Answer 3

Pale yellow solution reacts to form orange-brown precipitate

Question 4

What happens when Mn2+ reacts with NaOH and is left standing?

Answer 4

1. Pale pink solution reacts to become a light brown precipitate
2. Darkens due to oxidation

Question 5

What happens when Cr3+ is reacted with NaOH and then an excess of NaOH?

Answer 5

1. Violet solution reacts to form a grey/green precipitate
2. Soluble in excess NaOH to form a dark green solution

Question 6

What happens when Cu2+ is reacted with NH3 and then an excess of NH3?

Answer 6

1. Blue solution reacts to form a blue precipitate
2. Soluble in excess NH3 so a deep blue solution forms

Question 7

What happens when Fe2+ reacts with NH3 and is then left standing?

Answer 7

1. Pale green solution reacts to form a green precipitate
2. Oxidises to form and orange/brown precipitate

Question 8

What happens when Fe3+ reacts with NH3?

Answer 8

Pale yellow solution reacts to form and orange/brown precipitate

Question 9

What happens when Mn2+ reacts with NH3 and is left standing?

Answer 9

1. Pale pink solution reacts to form light brown precipitate
2. Darkens due to oxidation

Question 10

What happens when Cr3+ reacts with NH3 and then excess NH3?

Answer 10

1. Violet solution reacts to form a grey/green precipitate
2. Soluble in excess NH3 so forms a purple solution