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Molarity

Molarity is defined as the number of moles of solute dissolved in one liter of the solution or it can also be defined as number of millimoles of the solute dissolved in one milliliter of the solutionMolarity formulamolarity = number of moles ÷ volume of the solution in litersormolarity = g × 1000 ÷ m × v where g = weight of the solutev = volume of the solution in millilitersm = molecular weight of the solute


Molarity when density and percentage by weight are givenMolarity = 10 p d ÷ m where p = percentage by weight of soluted = density of the solutem = molecular weight of the soluteMolarity and Normality relationshipNormality = molarity × molar mass / eqivalent massFor acids


Normality = Molarity × BasicityFor Bases: Normality = Molarity × AcidityNote: Acidity is the number of H+ ions an acid can giveBasicity is the number of OH- ions a base can give 


Example 1Q:Calculate the molarity of the solution of volume 500 ml containing 4.9 g of sulfuric acid (H2SO4).solution: Molarity of the solution = number of moles of solute(H2SO4) / volume of the solution in litresNow calculate the number of moles of solute = mass of the solute / molar mass of soluteMolar mass of sulfuric acid = 98 gSo Number of moles = 4.9/98 = 0.05Now volume of the solution in litres = volume in ml / 1000= 500/1000 = 0.5 LSo molarity = number of moles / volume of the solution in litres= 0.05 / 0.5= 0.1 M 



 Example 2Q:Calculate the molarity of the solution of volume 100 ml containing 4 g of NaOH.Molarity of the solution = number of moles of solute(NaOH) / volume of the solution in litresNow calculate the number of moles of solute = mass of the solute / molar mass of soluteMolar mass of NaOH = 40 gSo Number of moles = 4/40 = 0.1Now volume of the solution in litres = volume in ml / 1000= 100/1000 = 0.1 LSo molarity = number of moles / volume of the solution in litres= 0.1 / 0.1= 1 M