Question

Five percent solution of solute (X) is isotonic with 0.855% solution of sucrose (molecular weight = 342 g). What is the molecular mass of solute (X)?
A. 200
B. 58.482
C. 400
D. 2000

Answer 1

Hint: Solution is a homogeneous mixture of two components called solute and solvent where solute is that substance which gets dissolved and solvent is that substance in which solute is dissolved and they both make a solution.

Complete answer:
The Solutions with a nonvolatile solute produce a vapor which is pure solvent while solutions with a volatile solute produce a vapor which is a mixture of both solvent and solute. There is another way to express the difference between volatile and nonvolatile: a nonvolatile solute does not appear as a component of the vapor above the solution while a volatile solute does appear as a component of the vapor above the solution.
It is given that the 5% solution of solute (X) is isotonic with 0.855% solution of sucrose. Two solutions are said to be isotonic if they have the same molar concentration.
Concentration of X = $(\dfrac{5}{M}\times \dfrac{1000}{100})=\dfrac{50}{M}g/L$
Concentration of sucrose = $M=\dfrac{342\times 50}{8.55}$
Now here both the given solution are isotonic in nature, this implies concentration of X will be equal to the concentration of sucrose so both the equations are said to be equal:
$\dfrac{50}{M}=\dfrac{8.55}{342}g/L$
$M=\dfrac{342\times 50}{8.55}$
M = 2000 g/L
Molecular mass of the solute is 2000.

Thus option D is the correct answer.

Note:
Solubility is defined as that property of a substance in which solute is dissolved in a solvent in order to form a solution. Solute is that substance which gets dissolved (present in small amount) and solvent in which solute is dissolved (present in higher amount).