THE MOLE: Formulae and Chemical Equations: Concentration of a solution

2.0 THE MOLE:Formulae and Chemical Equations

2.5 Concentration of a solution

How much solute we put in a given volume of liquid matters. We usually put just the right amount of salt, sugar, or other flavor in food; otherwise it tastes unpalatable. The amount of solute per unit volume (1 litre) of solution is called concentration.

1 litre = 1 dm³ = 1000 ml =1000 cm³ (1cm³ and 1ml are treated as equal)

Questions 2.5

1. Determine the concentration in g/dm³ of a solution containing (a) 5.85 g of sodium chloride in 1 dm³ (b) 5.85 g of the salt in 250 ml (c) 2.925 g of the salt in 500 ml.
2. Determine the concentration in g/dm³ of a solution containing (a) 40 g of sodium hydroxide in 500 ml (b) 40 g in 250 ml (c) 4 g in 500 ml.
3. Determine the concentration in g/dm³ of a solution containing 98 g of sulphuric (VI) acid in 1 dm³ (b) 98 g of sulphuric (VI) acid 500 ml (c) 49 g of sulphuric (VI) acid in 250 ml.
4. The concentration of a solution is 10 g/dm³. What is the mass of the solute in a 25-ml sample of the solution?
5. A beverage contains 10 g of sugar in 200 ml (1 cup) on average. Express this in g/dm³.

We notice from the results of calculations that concentration depends on both mass of solute and volume of solution. A small mass of solute can give a high concentration if the volume is small. A large mass can give a low concentration if dissolved in a large volume.