Question

When 20 g of non volatile solid is added to 250 ml of water, the freezing point of water becomes -0.9 celcius. calculate the molecular mass of the solid if freezing constant of water is 1.86

Answer 1

Answer:

-0.9×250=9.25

Explanation:

9.25×1.86=17.205 So here the answer is 17. 205.

Answer 2

The molecular mass of the solid is 165.33 gm.

- Given:

w = 20 g

V = 250 ml

ΔTf = 0.9

Kf = 1.86

- Since 1 ml water = 1 gm

⇒ 250 ml = 250 g =W

- We know that

ΔTf = Kf × m

ΔTf = Kf × (w × 1000)/ (M.wt × W)      

0.9 = 1.86 × (20 × 1000)/ (M.wt × 250)

M.wt = 148.8/0.9

M.wt = 165.33 gm