Concentration of solutions

Percent Composition (by mass)
You can consider percent by mass (or weight percent) in two ways:

  • The parts of solute per 100 parts of solution
  • The fraction of a solute in a solution multiplied by 100

You need two pieces of information to calculate the percent by mass of a solute in a solution:

  • The mass of the solute in the solution
  • The mass of the solution

Use the following equation to calculate percent by mass:

Mass Percentage = (Solute mass/Solution mass) X 100

Molarity
Molarity tells us the number of moles of solute in exactly one litre of a solution. (Note that molarity is represented by a capital M).
You need two pieces of information to calculate the molarity of a solute in a solution:

  • The moles of solute present in the solution
  • The volume of solution (in litres) containing the solute

To calculate molarity use the equation:

Molarity = Moles of solute/Volume of solution (L)

Molality
Molality, m, tells us the number of moles of solute dissolved in exactly one kilogram of solvent. (Note that molality is represented by a lower case m).
You need two pieces of information to calculate the molality of a solute in a solution:

  • The moles of solute present in the solution
  • The mass of solvent (in kilograms) in the solution

To calculate molality we use the equation:

Molality = Moles of solute/Mass of solvent (Kg)

Normal and Molar Soluions

Concentrated reagents   Specific gravity   Molarity   Normality   Volume (mL) required to make 1L of solution 
   SG M N   1M    1N  
 Acetic acid 99,5%     17,40 17,40 57,5 57,5
 Ammonia 35%   0,88 18,10 18,10 55,3 55,3
 Ammonia 25%   0,91 13,40 13,40 74,6 74,6
 Hydrochloric acid 36%   1,18 11,65 11,65 85,8 85,8
 Hydrochloric acid 32%   1,16 10,20 10,20 98,0 98,0
 Hydrofluoric acid 40%   1,13 22,60 22,60 44,2 44,2
 Nitric acid 70%   1,42 15,80 15,80 63,3 63,3
 Perchloric acid 60%   1,54 9,20 9,20 108,7 108,7
 Perchloric acid 70%   1,67 11,60 11,60 86,2 86,2
 Orthophosphoric acid 85%   1,70 15,20 45,60 65,8 21,9
 Sodium hydroxide 47%   1,50 17,60 17,60 56,7 56,7
 Sulfuric acid 96%   1,83 18,00 36,00 53,1 26,2