Exam (elaborations)
Calculations for Unit 3
- Institution
- PEARSON (PEARSON)
Some calculations for the concentration.
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3.3 Moles and volumesOCR Chemistry A Calculations
Units and concentration
Specification references
2.1.3 e) (i) (iii)
M0.0 Recognise and make use of appropriate units in calculations
M0.1 Recognise and use expressions in decimal and ordinary form
M1.1 Use an appropriate number of significant figures
M2.2 Change the subject of an equation
M2.3 Substitute numerical values into algebraic equations using appropriate
units for physical quantities
Learning outcomes
After completing the worksheet you should be able to:
recognise and make use of appropriate units in calculations
state the concentration of a substance in solution in units of mol dm−3
carry out calculations using concentration, volume and amount of substance
report answers to an appropriate number of significant figures.
Introduction
The concentration of a solution is defined in units of moles per cubic decimetre
(mol/dm3), which is called molar concentration. Since can also be represented
as dm−3 the unit of concentration can also be represented by mol dm−3.
By looking at the units of concentration of mol dm−3 we can see that the equation for
determining the concentration of a solution must be;
When calculating the concentration of a solution the volume must be given in units of
dm3. Therefore we need to be able to readily convert between units of m 3, dm3 and cm3
in order to correctly give the concentration of a solution. Figure 1 shows how to do this.
Figure 1 Converting between units of volume
© Oxford University Press 2015 www.oxfordsecondary.co.uk/acknowledgements
This resource sheet may have been changed from the original 1
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