GROUP 3+4

Question 1

The elements of group III react with NH4Cl and NH4OH till

Answer 1

alkaline to form hydroxides precipitated in basic solution

Question 2

Identification of chromium ions

Cr3+ + NaOH →

Answer 2

Cr(OH)3
greyish green ppt. that dissolve in excess NaOH

Question 3

Identification of ferric ions

Fe3+ + SCN- →

Answer 3

[FeSCN]+2
Blood red color

Question 4

Identification of aluminum ions

Al3+ + NaOH →

Answer 4

Al(OH)3
white ppt.

Question 5

adding NH4OH

Answer 5

to completely precipitate the cations as hydroxides.

Question 6

adding NH4Cl

Answer 6

to reduce the ionization of NH4OH by common ion effect.

Question 7

Identification of Zn+2

potassium ferrocyanide
2 Zn+2 + K4[Fe(CN)6]2 →

Answer 7

Zn2[Fe(CN)6]
(greenish White ppt)

Question 8

Identification of Co+2

AlcoholicKSCN in acetone
CoCl2 + 4 KSCN →

Answer 8

K2[Co(SCN)4] + 2 KCl
blue tetrathiocyanatocobaltate complex

Question 9

Identification of Ni+2

By 1 ml dimethylglyoxime

Answer 9

rose-red precipitate

Question 10

Thioacetamide in presence of aq. NH3 and NH4Cl

Answer 10

buff ppt (MnS)

Question 11

Lead dioxide and concentrated nitric acid

Answer 11

violet-red (or purple colour)

due to permanganic acid

Question 12

MnCl2 , ZnCl2

Answer 12

Soluble

Question 13

CoS, NiS

Answer 13

Insoluble

Question 14

Zn(OH)2 + 2 NaOH →

Zn(OH)2 is amphoteric

Answer 14

Na2 [ZnO2] + 2 H2O

Question 15

Mn(OH)2

Answer 15

does not dissolve
(remains as white precipitate)