Concentration tells you how much solute is in each cubic decimetre of solution. Measure a volume, and you know the amount. A titration uses this to find an unknown concentration. Knowing both units is core; the calculations are Extended content.
Concentration can be given in g/dm3 or in mol/dm3. Moles of solute = concentration in mol/dm3 × volume in dm3, and to change cm3 into dm3 you divide by 1000. In a titration you find the moles of the solution you know completely, use the equation's ratio, and then divide by the volume of the other solution in dm3.
Core: know that concentration is measured in g/dm3 and in mol/dm3. Extended: calculate with them, always using volumes in dm3.
Burettes and pipettes measure in cm3, but concentrations are per dm3. Forgetting to divide by 1000 makes 25 cm3 of 0.2 mol/dm3 look like 5 mol instead of 0.005 mol.
Four quick checks. Each correct answer earns XP and records this skill on your profile.
0.5 mol of solute is dissolved to make 2 dm3 of solution. What is the concentration?
What is 25 cm3 in dm3?
Which pair of units can both be used for concentration?
A solution of sodium hydroxide (Mr 40) has a concentration of 0.1 mol/dm3. What is this in g/dm3?
Run a titration in the simulator: fill the burette with acid, pipette 25.0 cm3 of alkali into the flask, add indicator, and open the tap until the colour just changes. Repeat until two titres agree within 0.10 cm3.
Sulfuric acid has two hydrogen ions per formula, so it reacts with sodium hydroxide in a 1 : 2 ratio. The ratio step is where the marks are won or lost.
Do not skip the ratio. Treating the sulfuric acid titration as 1 : 1 gives 0.0025 ÷ 0.0125 = 0.20 mol/dm3, double the right answer. Write the balanced equation first and read the ratio from it.
Unlocks once the four checks above are done. Worth more XP, written to IGCSE Paper 2 and Paper 4 standard.
How many moles of solute are in 25 cm3 of a 0.2 mol/dm3 solution?
25.0 cm3 of sodium hydroxide solution is neutralised by 20.0 cm3 of 0.10 mol/dm3 hydrochloric acid. What is the concentration of the sodium hydroxide?
25.0 cm3 of 0.10 mol/dm3 NaOH is neutralised by 12.5 cm3 of sulfuric acid. H2SO4 + 2NaOH → Na2SO4 + 2H2O. What is the concentration of the sulfuric acid?
What volume of 0.5 mol/dm3 hydrochloric acid exactly neutralises 0.01 mol of sodium hydroxide?
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