Question

15g of an unknown molecular material is dissolved in 450 g of water .The resulting solution freezes at -0.340C .What is the molar mass of the material?

Answer 1

ΔTf = Kf m -- (1) 

ΔTf = original freezing point of water – freezing point of solution  

= 273K - (-0.34 +273) K 

= 0.34 K 

M = give mass of solute / molar mass of solute x 1000 / mass of solvent  

= 15g/ M x 1000 g  kg raise to power –1 / 450g 

= 33.3 g kg raise to power –1 / M 

Kf for water  = 1.86 k Kg mol raise –1 

Putting the values in given equation 1 we get  

0.34K = 1.86 K Kg mol raise to power –1 x 33.3g kg raise to power –1 / M 

M = 1.86 K kg mol raise to power –1 x 33.3 g kg raise to power –1 / 0.34 K 

= 182.17 g mol -1

Answer 2

Explanation:

molecular mass is 182.35g/mol