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