Concentration in g/dm3

Concentration is a measure of how much of a substance is present in a given volume
The simplest way to show a calculation is in grams per decimetre cubed, g/dm³
This is calculated using the following equation:

$concentration = \frac{mass of solute (grams)}{volume of solution ({dm}^{3})}$

A solution contains 2.0g of sodium hydroxide in 200cm³ of water.

What is the concentration in g/dm³?

Answer

- $mass of solute = 2.0 g$
- $volume of solution in {dm}^{3} = \frac{200 {cm}^{3}}{1000} = 0.20 {dm}^{3}$
- $concentration = \frac{mass of solute}{volume of solution} = \frac{2.0 g}{0.20 {dm}^{3}} = 10 g / {dm}^{3}$

You may have to convert from g/dm³ into mol/dm³ and vice versa depending on the question
- To go from g/dm³ to mol/dm³:
  - Divide by the molar mass in grams
- To go from mol/dm³ to g/dm³:
  - Multiply by the molar mass in grams

A solution of sulfuric acid, H₂SO₄, has a concentration of 0.1 mol/dm³

What is the concentration in g/dm³?

Answer

- Both units are per decimetre cubed, so you just need to convert moles to mass, using the molar mass
- Molar mass of H₂SO₄ = 98 g/mol
- Mass of H₂SO₄ = moles (mol) x molar mass (g/mol)
- Mass of H₂SO₄ = 0.1 mol x 98 g/mol = 9.8 g
- This is the mass present in 1dm³ so the concentration = 9.8 g/dm³

Don't forget your unit conversions:

To go from cm³to dm³ : divide by 1000

To go from dm³ to cm³ : multiply by 1000

Concentration in g/dm3 (OCR Gateway GCSE Chemistry)