Question

On dissolving 15gm of a substance in 150fgm water a depression of 1.2°c in the freezing point is recorded .
calculate the molecular weight of the substance.
The molar depression constant of water is 1.86​

Answer 1

Answer:

where

Δ

T

f

= the decrease in the freezing point

K

f

= the molal freezing point depression constant of the solvent

m

= the molality of the solution

We can rearrange the formula to get

m

=

Δ

T

f

K

f

In your problem,

Δ

T

f

=

0.930 °C

K

f

=

1.86 °C⋅kg⋅mol

-1

∴  

m

=

0.930

°C

1.86

°C

⋅

kg⋅mol

-1

=

0.500 mol⋅kg

-1

Now,  

m

=

0.500 mol

1

kg

=

22.5 g

0.250

kg

∴  

1 mol

=

22.5 g

0.250

×

1

0.500

=

180 g

The molar mass is 180 g/mol, so the molecular mass is 180 u.

Explanation:

Answer 2

I hope answer in above image clear