TM:, NaOH and NH3

Question 1

Colour change when NaOH/NH3 added: Cr +3

Answer 1

Green solution➡️ grey-green precipitate

Question 2

Colour change when excess NaOH added: Cr +3

Answer 2

Grey-green precipitate➡️ dark green solution

Question 3

Colour change when excess NH3 added: Cr +3

Answer 3

Grey-green precipitate➡️ purple solution

Question 4

Colour change when NH3/NaOH added: Cu +2

Answer 4

Pale blue solution➡️ blue precipitate

Question 4

Colour change when excess NH3 added: Cu +2

Answer 4

Blue precipitate➡️ deep blue solution

Question 5

Colour change when NH3/NaOH added: Fe +2

Answer 5

Pale green solution➡️ green precipitate

Question 6

Why does the precipitate of Fe +2 darken on standing after NaOH/NH3 is added? (Also happens to Fe +3)

Answer 6

Precipitate is oxidised by water and O2 in the air and forms iron(lll) hydroxide

Question 7

Colour change when NH3/NaOH added: Fe +3

Answer 7

Yellow solution➡️ Orange precipitate

Question 8

Colour change when NaOH/NH3 added: Co +2

Answer 8

Pale pink solution➡️ blue precipitate

Question 9

Colour change when excess NH3 added: Co +2

Answer 9

Blue/pink precipitate➡️ yellow-brown solution

Question 10

What happens to the colour of Co +2 after NH3/NaOH has been added and its left to stand?

Answer 10

Turns brown

Question 11

What happens to the colour of Co +2 after NaOH/NH3 has been added and its left to stand?

Answer 11

Oxidised to form a brown solution