Using Concentrations of Solutions in mol/dm³ + Moles in Relation to Volumes of Gases

Write down the two formulae that link concentration, mass/moles and volume together.

Concentration (g/dm³) = Mass (g) / Volume (dm³) Concentration (mol/dm³) = Moles (mol) / Volume (dm³)

31.0 cm³ of potassium hydroxide solution neutralised 25.0 cm³ of 2.0 mol/dm³ nitric acid (HNO₃ + KOH ⟶ KNO₃ + H₂O). Calculate the concentration of the potassium hydroxide solution in mol/dm³. (Higher tier only)

Step 1: Moles HNO₃ = 2.0 x (25/1000) = 0.05 moles.

Step 2: Mole ratio is 1:1, so moles KOH = 0.05.

Step 3: Conc. KOH = 0.05 / (31/1000) = 1.61 mol/dm³.

What is titration?

A technique for finding the concentration of a solution by reacting a known volume of it with a solution of known concentration.

How do you conduct a titration?

1. Use a pipette to measure a known volume of the unknown solution into a flask.

2. Add an indicator.

3. Add the known solution from a burette gradually.

4. Stop when the indicator changes colour (the end point) and record the volume added.

5. Repeat until you get concordant results (volumes that are very close together).

What is the molar volume of a gas at room temperature and pressure (RTP)?

1 mole of any gas at room temperature and pressure occupies 24 dm³.