Precipitation reactions

Question 1

Describe the precipitation reactions of Fe3+?

Answer 1

• pale yellow solution which forms an orange brown precipitate of iron hydroxide
  -insoluble in excess sodium hydroxide
• Fe3+ (aq) + 3OH-(aq) = Fe(OH)3 (s)
  orange brown precipitate

Question 2

Describe the precipitation reactions of Mn2+?

Answer 2

• pale pink solution which forms a light brown precipitate of manganese hydroxide
• -insoluble in excess sodium hydroxide
  Mn2+ (aq) + 2OH-(aq) = Mn(OH)2

Question 3

Describe the precipitation reactions of Cu2+?

Answer 3

• forms a blue precipitate of copper ll hydroxide
  -insoluble in excess sodium hydroxide
  Cu2+ + 2OH- = Cu(OH)2

Question 4

Describe the precipitation reactions of Fe2+?

Answer 4

• pale green precipitate forms a green precipitate in iron hydroxide
• Fe2+ (aq) + 2OH- = Fe(OH)2
  -insoluble in excess sodium hydroxide
• The precipitate can be oxidised to form Fe (lll)
  Fe(OH)2 = Fe(OH)3

Question 5

Describe the precipitation reactions of cr3+?

Answer 5

• violet solution reacts with OH- to form a grey green precipitate
• Cr3+ + 3OH- = Cr(OH)3
  green precipitate
• soluble in sodium hydroxide and forms a dark green solution
• Cr(OH)3 + 3OH- = [Cr(OH)6]3-

Question 6

What is the reaction of cu(OH)2 and excess ammonia?

Answer 6

• forms a deep blue solution of [Cu(NH3)4(H20)2]2+

Question 7

What is the reaction of Cr(OH)3 and excess ammonia?

Answer 7

• a green precipitate which dissolves in excess ammonia to form [Cr(NH3)6]3+ which is a purple solution