Question

A chemical test has determined the concentration of a solution of an unknown substance to be 2.41 M. a 100.0 mL volume of the solution is evaporated to dryness, leaving 9.56 g of crystals of the unknown solute. Calculate the molar mass of the unknown substance.

Answer 1

Answer : The molar mass of unknown substance is, 39.7 g/mol

Explanation : Given,

Mass of unknown substance = 9.56 g

Volume of solution = 100.0 mL

Molarity = 2.41 M

Molarity : It is defined as the number of moles of solute present in one liter of volume of solution.

Formula used :

$\text{Molarity}=\frac{\text{Mass of unknown substance}\times 1000}{\text{Molar mass of unknown substance}\times \text{Volume of solution (in mL)}}$

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

$2.41M=\frac{9.56g\times 1000}{\text{Molar mass of unknown substance}\times 100.0mL}$

$\text{Molar mass of unknown substance}=39.7g/mol$

Therefore, the molar mass of unknown substance is, 39.7 g/mol