Question

Define the following terms: (i) Mole fraction (ii) Molality (iii) Molarity (iv) Mass percentage.

Answer 1

1)Mole fraction:Mole fraction is the ratio of number of moles of one component to the total number of moles of all components in the solution.
2)Molality:The number of moles of solute present in 1kg of solvent is called Molality.It is denoted by 'm'.
3)Molarity:The number of moles of solute present in one litre of solution is called molarity.It is denoted by 'M'.
4)Mass percentage:Mass percentage of a component in a given solution is the mass of the component per 100 gm of the solution.

Answer 2

Hey !!

(i) Mole fraction :- It may be defined as the ratio of the number of moles of one component (solute or solvent) to the total number of moles of all the components present in the solution.

If in a solution, na and nb are the number of moles of solvent and solute, then

Mole fraction of solvent in the solution

                 xa = na / na + nb

Mole fraction of solute in the solution

                 xb = nb / na + nb

In a solution, sum of the mole fractions of all the components is unity.

Example :- In a binary solution (having two components) xa + xb = 1

(ii) Molality :- It is defined as the number of moles of solute per 1000 g or 1 kg of solvent.

   Molality = Number of moles of solute / Mass of solvent in kg

(OR) m = n/W (or) m = Wb × 1000 / W × Wa

where n is number of moles of solute, Wa is weight of solvent, Wb is quantity of solute, Mb is molar mass of solute. Molality and mole fraction do not change with change in temperature.

Units :- kg⁻¹ or molal (m)

(iii) Molarity :- It is defined as number of moles of solute dissolved in one litre of solution.

         Molarity = Moles of solute / Volume of solution (in litre)

Units :- mol L⁻¹ or M (molar)

(iv) Mass percentage :- It may be defined as mass of solute per 100 g of solution.

    Mass% of solute = Mass of solute / Total mass of the solution × 100

Good luck !!