# REACTIONS IN SOLUTION

Molarity

• Molarity (M) is defined as number of moles of solute dissolved in one litre (or one cubic decimetre) of solutio

• where WB is the mass of solute and MB is the molar mass of the solute.
• For dilution; where M1 is initial molarity, V1 is initial volume, M2 is final molarity and M2 is final volume.
• M1V1 = M2V2
•  are called molar, decamolar, decimolar, pentimolar, semimolar and centimolar solution respectively.

Molality

• Molality (m) is defined as the number of moles of the solute per kilogram (kg) of the solvent and is expressed as:

• Molality (m) = (Given mass / molecular mass) * ( 1/mass of solvent in Kg )
• Its SI unit is moles / Kg
• It is represented as m or molal solution.

Difference between Molarity and Molality

 Molarity Molality The molarity of a given solution is defined as the total number of moles of solute per litre of solution. Molality is defined as the total moles of a solute contained in a kilogram of a solvent. Mathematical expression is M = number of moles of the solute / Volume of solution given in terms of litres. The mathematical expression m = Number of moles of solute / Mass of solvent in Kg Depends on the volume of the whole solution. Depends on the mass of the solvent. Unit sign expressed as (M). Unit sign expressed as (  ). Molarity has a unit of moles/litre. Molality has a unit of moles / kg

Vapour density

• Vapor density is the ratio of the mass of a volume of a gas, to the mass of an equal volume of hydrogen, measured under the same conditions of temperature and pressure.
• It is a unitless quantity.

Relation between Vapour density and Molecular weight

• Molecular weight = 2 X Vapour density

Normality

• Normality (N) It is defined as the number of g-equivalents of solute per litre of solution or as the number of mg-equivalents of a substance per millilitre of solution.

• If specific gravity is known, normality is calculated as