Discovering chemistry
Discovering chemistry

Start this free course now. Just create an account and sign in. Enrol and complete the course for a free statement of participation or digital badge if available.

Free course

Discovering chemistry

3.3 Working with solutions: concentration

In making a solution, the chemicals involved are dissolved in a liquid which is referred to as the solvent.

The substance that dissolves is called the solute.

The most common solvent is water, but in the laboratory a chemist may choose to work with any one of a number of others. Different substances dissolve more easily or less easily in a particular solvent i.e. they have different solubilities. Here the solubility of a substance is defined as the maximum amount of solute that will dissolve in a given amount of solvent.

For example, when common salt (sodium chloride, the solute) is dissolved in water (the solvent) this gives a solution of sodium chloride. The solubility of a substance varies with temperature and is usually expressed as the maximum amount of a substance that will dissolve in 100 g of water at a particular temperature. However, it is often more usual (and more useful) to express the amount of solute that is dissolved in a specific volume of solution at a particular temperature.

This is known as the concentration of a solution, which is expressed as the amount of solute in 1dm 3.

Thus, if 10.0 g of sodium chloride is dissolved in water to give 1 dm3 of solution, the concentration would be 10.0 g per dm3 and so we would write 10.0 g dm3.

One important point: it is essential to define concentration as the amount of solute in exactly 1 dm 3, that is in 1 dm 3 of the final solution rather than the amount of solute dissolved in 1 dm3 of water. If you did dissolve 10.0 g of sodium chloride in 1 dm3 of water then the final volume would in effect be greater than 1 dm3. Therefore to make up a solution with a particular concentration of a solute, the required amount of solute is firstly dissolved fully in a suitable amount of water (less than 1 dm3) and then sufficient water is added to achieve the correct final volume of 1 dm3 .

Note 1dm3 = 1 litre

This is a label from a bottle of mineral water. It shows the concentration of each of the solutes expressed as mg/l.

Described image
Figure 8 Label from a bottle of mineral water
DC_1

Take your learning further

Making the decision to study can be a big step, which is why you'll want a trusted University. The Open University has 50 years’ experience delivering flexible learning and 170,000 students are studying with us right now. Take a look at all Open University courses.

If you are new to University-level study, we offer two introductory routes to our qualifications. You could either choose to start with an Access module, or a module which allows you to count your previous learning towards an Open University qualification. Read our guide on Where to take your learning next for more information.

Not ready for formal University study? Then browse over 1000 free courses on OpenLearn and sign up to our newsletter to hear about new free courses as they are released.

Every year, thousands of students decide to study with The Open University. With over 120 qualifications, we’ve got the right course for you.

Request an Open University prospectus371