question_answer 15)

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

Answer:

(i) Mole fraction. It is the ratio of the number of moles of a component (solute or solvent present) to the total number of moles of all components in the solution. Suppose a solution contains n, moles of A and n2 moles of B. Then Mole fraction of A,            Mole fraction of B,              It should be noted that x1 + x2 = 1 (ii) Molality. It is defined as the number of g-moles of solute dissolved in 1000 g (1 kg) of the solvent. It is denoted by m. Its units are moles kg-1. (iii) Molarity. It is defined as the number of gram-moles of solute dissolved per litre of the solution. It is denoted by M. Its units are mole It-1.   (iv) Mass percentage. In case of a solid dissolved in a liquid, the percentage by weight means the amount of solute in grams present in 100 g of the solution. Weight percentage     10% solution of sugar by weight means that 10 g of sugar is present in 100 g of the solution i.e., 10 g of sugar has been dissolved in 90 g of water. Percent by weight has the same meaning in case of a solution of a liquid in liquid.