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Concentration (Edexcel GCSE Chemistry: Combined Science)
Revision Note
Calculating Concentration
- A solid substance that dissolves in a liquid is called a solute, the liquid is called a solvent and the two when mixed together form a solution
- Most chemical reactions occur between solutes which are dissolved in solvents, such as water or an organic solvent
- Concentration simply refers to the amount of solute there is in a specific volume of the solvent
- The greater the amount of solute in a given volume then the greater the concentration
- A general formula for concentration is thus:
- Concentration can be measured in grams per cubic decimetre
- 1 decimetre cubed (dm3) = 1000 cm3
- 1 decimetre cubed (dm3) is the same as 1 litre
- You may be given data in a question which needs to be converted from cm3 to dm3 or the other way around
- To go from cm3 to dm3 :
- Divide by 1000
- To go from dm3 to cm3 :
- Multiply by 1000
- To go from cm3 to dm3 :
Worked example
A student dissolved 10 g of sodium hydroxide, NaOH, in 2 dm3 of distilled water. Calculate the concentration of the solution.
Answer:
Examiner Tip
Be careful when doing volume unit conversions as it is easy to multiply instead of dividing by 1000 and vice-versa. Always ask yourself – is the result going to be a bigger or smaller number than I started with? Do I get more or fewer cubic decimetres when I convert from cubic centimetres?
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