Concentration Of Solution - Higher - OCR 21st Century - BBC Bitesize

In this guide

1. Revise
2. Video
3. Test

Pages

1. Reactions of acids and alkalis
2. How to titrate an acid and an alkali
3. Concentration of solution - Higher
4. Calculating concentrations - Higher

Concentration of solution - Higher

A solution forms when a solute dissolves in a solvent. The concentration of a solution is a measure of the amount of solid dissolved in 1 dm3 of solution. When the mass of solute dissolved is measured in g, the units for concentration are g/dm3.

Key factconcentration (g/dm3) = \(\frac{mass\ of\ solute\ (g)}{volume\ (dm^3)}\)

Question

8 g of sodium hydroxide is dissolved in 2 dm3 of water. Calculate the concentration of the sodium hydroxide solution formed.

Show answer

concentration = \(\frac{mass\ of\ solute\ in\ g}{volume\ in\ dm^3}\)

concentration = \(\frac{8\ g}{2\ dm^3}\)

= 4 g/dm3

Volume units

Apparatus used to measure volumes is usually marked in cm3 or ml. Although these are different units, they describe the same volume. For example, 250 ml = 250 cm3.

Volumes used in concentration calculations must be in dm3, not in cm3 or ml. It is useful to know that 1 dm3 = 1,000 cm3. This means:

• divide by 1,000 to convert from cm3 to dm3
• multiply by 1,000 to convert from dm3 to cm3

For example, 250 cm3 is 0.25 dm3 (250/1,000). It is often easiest to convert from cm3 to dm3 before continuing with a concentration calculation.

Question

100 cm3 of dilute hydrochloric acid contains 0.5 g of dissolved hydrogen chloride. Calculate the concentration of the acid in g/dm3.

Show answer

volume of acid in dm3 = \(\frac{100}{1000}\) = 0.1 dm3

concentration = \(\frac{mass\ of\ solute\ in\ g}{volume\ in\ dm^3}\)

= \(\frac{0.5}{0.1}\)

= 5g/dm3

Next pageCalculating concentrations - HigherPrevious pageHow to titrate an acid and an alkali

More guides on this topic

• Separating chemical mixtures
• Finding the composition of unknown samples
• Calculating amounts of substances
• Calculating yields - OCR 21st Century
• Sample exam questions - chemical analysis

Related links

• Chemistry: Exam practice
• Chemistry revision resources
• Bitesize revision podcasts
• Personalise your Bitesize!
• Jobs that use Chemistry
• Save My Exams Subscription
• Quizlet
• Royal Society of Chemistry
• Revisio Subscription
• Science Museum