Depression in freezing point- source : surfguppy.com

### Solution )

w = 3.0 gm ,  ΔTf =1.45 0 C , Kf = 1.86 ,W =22 gm , m = ?

m =1000 K. w /ΔTf .W

m = 1000 x 1.86 x 3.0 / 1.45 x 22

m =174.9 = 175  Ans.

### Solution )

ΔTf = 2.0 , molality = 0.25

KfΔTf / molality

Kf = 2.0 /0.25 = 8.0 K Kg /mole Ans.

### For ‘A’ ,

w1= 4 gm,W1 = 100 gm ,

#### For ‘B’

w2= 4 gm,W2 = 100 gm ,

#### ΔTf2 = 0.2

m = 1000 Kf. w/ ΔTf.W

Because values of Kf , W and w  are same . Therefore ,

mA /mB =   ΔTf2 / ΔTf1

= 0.2 /0.1

= 2 /1

### For Acetone ,

w = 1.4 gm , W = 100 gm ,m of acetone [ CH3COCH3] = 12+ 3+12+ 16 + 12 + 3 = 58

#### m =1000 Kf . w /ΔTf .W

Kf = ΔTf .W.m / 1000 w

Kf = 1.28 x 100 x 58 /1000 x 1.4

### Kf = 5.30

For ‘A’,

w = 2.8 gm ,

W = 100 gm , m of ‘A’ =?

#### m =1000 Kf . w /ΔTf .W

m = 1000 x 5.30 x 2.8 / 0.64 x 100

### w = 2.71 gm ,

W =  72 gm , molecular weight  of  sulphur  ‘m’ = ?

#### m =1000 Kf . w /ΔTf .W

m = 1000 x 6.9 x 2.71 / 1.015 x 72

### m =255.8

molecular weight of sulphur = 255.8

Atomic weight of sulphur = 32

Number of atoms = molecular weight of sulphur / Atomic weight of sulphur

Number of atoms = 255.8 /32 = 7.9  = 8 atoms Ans.