Chapter 12, Problem 12.1QE

Interpretation Introduction

Interpretation:

The unit of quantity of solution has to be expressed for molarity, mole fraction and mass percentage.

Explanation of Solution

Molarity:  Molarity is defined as the mass of solute in one liter of solution.  Molarity is the preferred concentration unit for stoichiometry calculations.  The formula is,

  $\text{Molarity=}\frac{\text{Mass}\text{of}\text{solute(in}\text{grams)}}{\text{Volume}\text{of}\text{solution}\text{(in}\text{litres)}}$

The quantity of solution in molarity is expressed in terms of volume of solution in liters.

Mole fraction:  Mole fraction of a substance in a solution is the number of moles of that substance divided by the total number of moles of all substances present.  The formula is,

  $\begin{array}{l}{\text{χ}}_{\text{A}}\text{=}\frac{\text{Moles}\text{of}\text{A (in}\text{mol)}}{\text{Moles}\text{of}\text{A (in mol) +Moles}\text{of}\text{B (in mol) +Moles}\text{of}\text{C (in mol) +}\mathrm{...}}\\ \\ {\text{χ}}_{\text{A}}\text{=}\frac{\text{Moles}\text{of}\text{A (in}\text{mol)}}{\text{Total}\text{number}\text{of}\text{moles}\text{of}\text{components}\text{(in}\text{mol)}}\end{array}$

The quantity of solution in mole fraction is expressed in terms of total number of moles of the components present in the solution (in mol).  The sum of the mole fractions of all components of a solution is always one.

Mass percentage:  The mass percentage gives the number of grams of solute present in 100g of solution.  The formula of mass percentage is,

  $\text{Mass}\text{percentage=}\frac{\text{Grams}\text{of}\text{solute}}{\text{Grams}\text{of}\text{solution}}\text{×100\%}$

The quantity of solution in mass percentage is expressed in terms weight of the solution (in grams).