## A Chemical Cook Book

### Pfizer

Some aspects of volumetric analysis are discussed in this lesson. The common methods of expressing concentration are explained and there are worked examples of how to calculate concentration.

Contains the full lesson along with a supporting toolkit, including teachers’ notes.

### Lesson excerpt

Volumetric analysis is a branch of quantitative analysis that involves reacting measured volumes of solutions and the use of these volumes to calculate concentrations. Volumetric flasks are used to make up accurate volumes of solutions to ensure accurate concentrations, while burettes and pipettes are used to dispense accurate volumes of these liquids. The areas of the apparatus where the volumes are measured are narrow to ensure they are accurate. It is important to be able to read volumes with accuracy to 0.1cm3. Although cm3 is used in calculations, a millilitre (ml) is also a common unit used for measuring volumes of liquids. Millilitres (ml) are more commonly used in industry.

What is a solution?
A solution is a substance made up of a solute and a solvent. A solute is normally a soluble solid whereas a solvent is the liquid used to dissolve it – most commonly, water. Solutes and solvents can be broadly described as polar or non-polar. Water is a polar solvent and typically dissolves polar solutes. Alcohol and ethyl benzene are examples of solvents used for non-polar solutes.

If a solution contains a large amount of solute relative to the amount of solvent it is said to be concentrated. If a solution contains only a relatively small amount of solute then it is said to be dilute. In accurate quantitative analysis we need to know the exact amounts and concentration of solutions. The concentration of a solution is the amount of solute dissolved in a specified amount of solution.

### True or False?

1. Volumetric analysis is a branch of qualitative analysis. false
2. The concentration of a solution is the amount of solvent dissolved in a certain amount of solute. false
3. Qualitative analysis tells us what substances are present in a sample. false
4. A solution is a substance made of a solvent and a solute. false
5. The symbol M indicates the number of moles of solute per litre. true
6. The term p.p.m. is the equivalent of 1 gram of solute per litre. false
7. A solution labelled 10% w/v NaOH contains 10 g of solute per litre. true
8. Polar solutes dissolve in non-polar solvents. false
9. Narrow measuring containers give more accurate volumes . true
10. Pesticide concentrations in water are measured in mg/L. true
11. To make a 2 M solution you add two moles of solute to 2 two litres of water. false