precipitation reactions

Question 1

Cu²+ with hydroxide ions

Answer 1

blue solution ——> blue ppt forms

Cu2+ +2OH- —-> Cu(OH)2 (s)

INSOLUBLE IN EXCESS

Question 2

Fe2+ with hydroxide ions

Answer 2

pale green sol ——> green ppt

surface turns brown in standing air as Fe2+ is oxidised

INSOLUBLE IN EXCESS OH-

Question 3

Fe3+ with OH-

Answer 3

pale yellow sol —-> orange/brown ppt

insoluble in excess

Question 4

Mn2+ with OH-

Answer 4

pale-pink sol ——> light brown ppt

DARKENS slightly on standing air

insoluble in excess

Question 5

Cr3+ with OH-

Answer 5

violet sol —-> grey green ppt

SOLUBLE IN EXCESS

grey green ppt —> dark green sol

Cr(OH)₃ + 3OH- ——> [Cr(OH)₆)]³-(aq)

Question 6

Cu 2+ with Excess NH3

Answer 6

TWO STEPS

1
blue sol ——-> blue ppt
Cu2+ + 2OH- —-> Cu(OH)₂

2
blue ppt ——-> deep blue sol.

Cu(OH)₂ + 4NH₃ ——-> [Cu(NH3)₄(H20)₂]

Question 7

Cr3+ with drops of ammonia then excess ammonia

Answer 7

TWO STEPS
1.
violet sol. —-> grey green ppt

Cr3+ + 3OH- ——> Cr(OH)₃

2.
grey green ppt —-> purple sol

Cr(OH)₃ +6NH₃ —-> [Cr(NH₃)₆]