Concentration of solutions

Solution

solution is a mixture of two or more substances in a single liquid phase. one constituent is regarded the solvent and the others as solutes. Solute + Solvent = Solution

Solute

the part of the solution that is being dissolved (usually the lesser amount)

Solvent

the part of the solution that dissolves the solute (usually the greater amount)

What is solution concentration?

Indicates the amount of solute in a given amount of solution/solvent.

Types of concentrations - percent concentration

• weight/weight percent concentration

• weight/volume percent concentration

• volume/volume percent concentration

weight/weight percent concentration is defined by the following equation

• shows the percent of the solute

weight/volume percent concentration

• shows the weight of the solute in the total volume of solution

volume/volume percent concentration

• used with liquid solutes

• volume is expressed in millilitres (mL)

Solution density

Refers to the ratio between the weight and volume of a give solution. Two types of density are used: relative density, mass density

Relative density (d)

a digit that shows how much the weight of a given solution is bigger than the weight of an equal vol of water

Mass density (ρ)

• ρ (density) = m (mass solution)/ v (vol solution)

  • expressed as kg/cm³ or g/mL

Molarity

• It is the number of moles of solute pre litre of solution (mol/L or M)

How to calculate moles?

How to calculate concentration?

Conc = moles/vol

How to calculate molarity as two equations?

1. first determine the moles of solute (n=m/Mr)

   1. once you have n substitute in the molarity equation

Suppose you dissolve 15 g of KCl (Mr=74.55M_r = 74.55Mr​=74.55 g/mol) in 500 mL (0.500 L) of solution.

Molal concentration (Cm)

• shows the number of moles of a solute in 1000g of solvent

  • Molality is a measure of concentration that expresses the number of moles of solute per kilogram of solvent.

Key differences between molarity and molality