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Question 3

Define the following terms:

(i) Mole fraction    (ii) Molality    (iii) Molarity   (iv) Mass percentage.

Answer

a) Mole Fraction - it is defined as the ratio of number of moles of one component to the total number of moles of solute & solvent present in the solution.

Mole fraction = number of moles of the component / total number of moles of all components

It is denoted by x.

Take it as binary solution, the number of the moles of solute will be nA and the number of moles of solvent will be nB, then the mole fraction of the solute in the solution is given as:



In the same manner, the mole fraction of the solvent in the solution is given as:

 

b) Molality- it is the number of moles of the solute dissolved per 1000g of the solvent.

It is denoted by m

Molality = mole of solute / mass of solvent in kg

Unit for molality are moles/kg

 

c) Molarity- it is the number of moles of the solute dissolved per litre of the solution.

It is represented by M.

Molarity = moles of solute / volume of solute in litres

Unit for molarity is moles/litre

 

d) Mass Percentage- the mass percentage of a component in a given solution is the mass of the component per 100g of the solution.

Mass percentage of the component = (mass of the component in the solution/total mass of the solution) x100

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