The concentration of a solution tells you how much solute is dissolved in 1 unit volume of solution.
The volume of a solution is measured in dm³ (litres). 1 dm³ = 1000 cm³.
The amount of solute can be measured in grams or moles.
2 units of concentration used in chemistry are g dm^-3 and mol dm^-3

Concentration is the number of moles of solute per liter of solution.
A concentration of 10 g dm^-3 means there is 10 g of solute dissolved in1 dm³ of solution.

Concentration = Mass of solute(g) Volume of solution(dm 3 )

Example 1:

Calculate the concentration of the solution if 28g of NaOH is dissolve in 250cm³ of water.

Answer:

Mass of solute = 28g
Volume of solvent = 250cm³ = 0.25dm³

Concentration= Mass/Volume = 28g/0.25dm³ = 112g/dm³

Molarity is probably the most commonly used unit of concentration. It is the number of moles of solute per liter of solution.
A concentration of 2 mol dm^-3 means there are 2 moles of solute dissolved in 1 dm³ of solution.

Molarity = Mole of solute(mol) Volume of solution(dm 3 )

Example:

What is the molarity of a solution made when water is added to 0.2 mol of CaCl₂ to make 100 cm³ of solution? [RAM: Ca = 40; Cl = 35.5]

Answer:

Number of mole of solute = 0.2 mol
Volume of solvent = 100 cm³ = 0.1 dm³

Molarity = Number of Mole/Volume = 0.2mol/0.1dm³ = 2mol/dm³

6.5.2 Concentration of Solution

Concentration of a Solution