Titration concentration
moles = concentration x volume(dm3) [volume in cm3 → divide by 1000]
Two easy marks are lost every year to the cm^3 -> dm^3 conversion. Do the acid side first.
Work it, then mark it
Do each calculation on paper first, then reveal the mark scheme and tick the marks you actually earned — the same way you should mark past papers.
In a titration, 25.0 cm3 of sodium hydroxide solution is exactly neutralised by 20.0 cm3 of 0.10 mol/dm3 hydrochloric acid. The equation is NaOH + HCl → NaCl + H2O. Calculate the concentration of the sodium hydroxide in mol/dm3.
Do the calculation on paper first — then mark it.
Where the marks get lost
- Forgetting to divide the cm3 volume by 1000 to get dm3.
- Using the wrong volume for the wrong chemical (25.0 goes with the NaOH, 20.0 with the HCl).
- Ignoring the mole ratio from the balanced equation (it happens to be 1:1 here, but check every time).
Exam tip: Always work moles = concentration x volume(in dm3). Find the moles of the chemical you know first, use the ratio, then rearrange for the unknown concentration.
Calculations are the most trainable marks in chemistry
They come up every paper and reward a clean method. Send me one you keep dropping marks on — your first lesson is free.