Concentration of a Solution
- 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 in g 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
Concentration in mol dm-3 (Molarity)
- 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