Concentrations of Solutions (OCR GCSE Chemistry A, Combined (Gateway Science Suite)): Revision Notes
📚 Revision Notes
3.2.5 Concentrations of Solutions
What is Concentration?
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The concentration tells us how much solute (the substance that's dissolved) is in a certain volume of solvent (the liquid it's dissolved in). A solution with a high concentration has more solute in it than a solution with a low concentration.
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Concentration is usually measured in grammes per cubic decimetre (g/dm³). 1 dm³ is equal to 1000 cm³, so it's a larger volume.
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Calculating Concentration:
- To calculate the concentration of a solution, use the formula:
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Example: If you dissolve 25 grammes of sodium chloride () in 1000 cm³ of water (which is 1 dm³), the concentration is:
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Using Moles to Calculate Concentration:
- You can also calculate concentration using moles instead of grammes:
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Example: If you dissolve 0.5 moles of in 2 dm³ of water, the concentration is:
Summary:
- Grams per dm³: Used when the mass of the solute is known.
- Moles per dm³: Used when the amount of solute is measured in moles.