Define the following terms:

Question:

Define the following terms:

(i) Mole fraction

(ii) Molality

(iii) Molarity

(iv) Mass percentage.

Solution:

(i) Mole fraction:

The mole fraction of a component in a mixture is defined as the ratio of the number of moles of the component to the total number of moles of all the components in the mixture.

i.e.,

Mole fraction of a component $=\frac{\text { Number of moles of the component }}{\text { Total number of moles of all components }}$

Mole fraction is denoted by ‘x’.

If in a binary solution, the number of moles of the solute and the solvent are nA and nB respectively, then the mole fraction of the solute in the solution is given by,

$x_{A}=\frac{n_{A}}{n_{A}+n_{B}}$

Similarly, the mole fraction of the solvent in the solution is given as:

$x_{B}=\frac{n_{B}}{n_{A}+n_{B}}$

(ii) Molality

Molality (m) is defined as the number of moles of the solute per kilogram of the solvent. It is expressed as:

Molality $(\mathrm{m})=\frac{\text { Moles of solute }}{\text { Mass of solvent in } \mathrm{kg}}$

(iii) Molarity

Molarity (M) is defined as the number of moles of the solute dissolved in one Litre of the solution.

It is expressed as:

Molarity $(M)=\frac{\text { Moles of solute }}{\text { Volume of solution in Litre }}$

(iv) Mass percentage:

The mass percentage of a component of a solution is defined as the mass of the solute in grams present in 100 g of the solution. It is expressed as:

Mass $\%$ of a component $=\frac{\text { Mass of component in solution }}{\text { Total mass of solution }} \times 100$

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