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Ymorist [56]
3 years ago
12

Calculate the molecular weight of a substance. In which the solution of this substance in the water has a concentration of 7 per

cent by weight, has a freezing point
Equal to -0.89 ° C, set Kf value of water = 1.86 ° C / m
Chemistry
1 answer:
Eduardwww [97]3 years ago
7 0

Answer : The molecular weight of a substance is 157.3 g/mol

Explanation :

As we are given that 7 % by weight that means 7 grams of solute present in 100 grams of solution.

Mass of solute = 7 g

Mass of solution = 100 g

Mass of solvent = 100 - 7 = 93 g

Formula used :  

\Delta T_f=i\times K_f\times m\\\\T_f^o-T_f=k_f\times\frac{\text{Mass of substance(solute)}\times 1000}{\text{Molar mass of substance(solute)}\times \text{Mass of water(solvent)}}

where,

\Delta T_f = change in freezing point

T_f^o = temperature of pure water = 0^oC

T_f = temperature of solution = -0.89^oC

K_f = freezing point constant of water = 1.86^oC/m

m = molality

Now put all the given values in this formula, we get

(0-(-0.89))^oC=1.86^oC/m\times \frac{7g\times 1000}{\text{Molar mass of substance(solute)}\times 93g}

\text{Molar mass of substance(solute)}=157.3g/mol

Therefore, the molecular weight of a substance is 157.3 g/mol

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