Ncert Exercises & Solutions

Define the following modes of expressing the concentration of a solution? Which of these modes are independent of temperature and why?

1. w/w (mass percentage)

2. V/V (volume percentage)

3. w/V (mass by volume percentage)

4. ppm (parts per million)

5. $χ$ (mole fraction)

6. M (molarity)

7. m (molality)

(a) w/w (mass percentage) Mass percentage of a component of a solution can be expressed as

Mass % of component =

\frac{mass of component in the solution}{total mass of solution} \times 100

Thus, the percentage by mass means the mass of the solute in grams present in 100g of the solution.

(b) V/V (volume percentage) is defined as

Volume percentage =

\frac{volume of the component}{total volume of solution} \times 100

Thus, volume percentage means the volume of the liquid solute in cm³ present in 100 cm³ of the solution.

(c) w/V (mass by volume percentage) = mass of solute dissolved in 100 mL. of solution.

(d) ppm (parts per million) This parametre is used to express the concentration of very dilute solution.

ppm =

\frac{number of parts of component}{total number of parts of all component of solution} \times 10^{6}

(e) $χ$ (mole fraction) Mole fraction is an unitless quantity used to determine extent of any particular component present in total solution.

χ = \frac{number of moles of the component}{total number of moles of all components}

(f) M (molarity) Number of moles of solute dissolved in per litre of solution is known as molarity.

M = $\frac{number of moles of solute}{volume of solution in litre}$

(g) m (Molality) Molality of any solution can be defined as number of moles of solute dissolved in per kg of solvent.

m = $\frac{number of moles of solute}{mass of solvent in kg}$