|Solute||Solid which dissolves|
|Solvent||Liquid which does the dissolving|
|Solution||Solute + solvent|
|Saturated solution||A solution which will dissolve no more solute.|
|Soluble substance||A substance that will dissolve in a solvent.|
|Insoluble substance||A substance that will not dissolve in a solvent|
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 )
Calculate the concentration of the solution if 28g of NaOH is dissolve in 250cm3 of water.
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 )
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]
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
Conversion of the Unit of Concentration
- The chart above shows how to convert the units of concentration from g dm-3 to mol dm-3 and vice versa.
- The molar mass of the solute is equal to the relative molecular mass of the solute.
The concentration of a Potassium chloride solution is 14.9 g dm-3. What is the molarity ( mol dm-3) of the solution? [ Relative Atomic Mass: Cl = 35.5; K = 39 ]
Relative Formula Mass of Potassium Chloride (KCl)
= 39 + 35.5 = 74.5
Molar Mass of Potassium Chloride = 74.5 g/mol
Molarity of Potassium Chloride
Molarity = Concentration Molar Mass = 14.9gd m −3 74.5gmol−1 =0.2mol/dm3
A solution of barium hydrokxide have molarity 0.1 mol dm-3. What is the concentration of the solution in g dm-3? [Relative Atomic Mass: Ba = 137; O = 16; H = 1 ]
Relative Formula Mass of barium hydrokxide, Ba(OH)2
= 137 + 2(16+1) = 171
Molar Mass of Potassium Chloride = 171 g/mol
= Molarity×Molar Mass
=0.1mol/dm3 × 171gmol−1 =17.1gmol−1