10.03.06 Concentration of Solutions (g/mol)

Syllabus

- Many chemical reactions take place in solutions.
- The concentration of a solution can be measured in grams per dm3 (g/dm3 ).
- Students should be able to calculate the mass of solute in a given volume of solution of known concentration in terms of mass per given volume of solution

(HT only) explain how the mass of a solute and the volume of a solution is related to the concentration of the solution.

We dilute squash with water until it tastes right

One way to measure a concentration is the number of grams of solute (dissolved stuff) in each litre of water

Unfortunately, chemists write litres as dm3

So the unit would be grams per dm3 (g/dm3) rather than g/L which would be easier.

A student dissolves 16 g of salt in 2 dm3 of water what is the concentration?

Concentration = Mass/ volume = 16/2 = 8 g/dm3.

A student dissolves 16 g of salt in 200 cm3 of water what is the concentration?

Concentration = Mass/ volume

But first we need to know how many dm3 of water were used.

1000 cm3 = 1 dm3

So, 200 cm3 = 200/100 = 0.2 dm3

Concentration = g/ dm3 = 16/0.2 = 80 g/dm3.

A student has a salt solution with concentration 2.5 g/dm3.

What mass of salt in 4 dm3 of water?

Concentration = Mass/ Volume

So, Mass = Concentration x Volume

Mass = 2.5 x 4 = 10g

A student has a salt solution with concentration 3.5 g/dm3.

What mass of salt in 400 cm3 of water?

Concentration = Mass/ Volume

But first we need to know how many dm3 of water were used.

1000 cm3 = 1 dm3

So, 400cm3 = 400/1000 = 0.4 dm3

Mass = Concentration x Volume

Mass = 3.5 x 0.4 = 1.4 g