How to carry out and record an acid–base titration, choose an indicator, identify concordant titres, and use the results with the mole ratio to find a concentration.
5 narrated scenes. Press play, listen and read along — the points appear as they are explained. Use ‹ Prev / Next › or the scene bar to jump to any scene.
A titration is the chemist’s most precise way of finding how much acid is in a solution. It combines careful lab technique with the mole concept — the two areas where candidates lose most marks.
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Copy these into your notebook in your own words — that is how they stick.
Pipette: fixed volume; burette: variable volume, read to 0.05 cm³.
Burette and pipette with the solution they hold; flask with distilled water.
Final reading − initial reading; readings to 2 d.p.
Titres within 0.10 cm³; average only these.
Methyl orange (strong acid/weak alkali); phenolphthalein (weak acid/strong alkali).
V in cm³.
Use the balanced equation (HCl:NaOH 1:1; H₂SO₄:NaOH 1:2).
moles known → mole ratio → moles unknown → concentration.
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8 items modelled on real CSEC Paper 1 questions. Choose one answer for each, then check. Aim for 80% or better. Work each item on paper first.
Write full answers, then reveal the mark scheme and tick the points you earned (16 marks in total). Show all your working — method marks count. Your answers are saved on this device.
Question 1 [16 marks]
25.0 cm³ portions of sodium hydroxide solution were titrated against 0.100 mol/dm³ hydrochloric acid using methyl orange. Burette readings (cm³): trial 0.00 → 21.30; titration 1 0.50 → 20.60; titration 2 0.20 → 20.35; titration 3 1.00 → 21.30.
(a) (a) Calculate the titre for each titration. [3]
(b) (b) State which titres are concordant and calculate the average titre. [3]
(c) (c) Calculate the number of moles of hydrochloric acid in the average titre. [3]
(d) (d) Write the equation and calculate the concentration of the sodium hydroxide solution. [4]
(e) (e) State the colour change of methyl orange at the end-point. [1]
(f) (f) State two precautions that improve accuracy. [2]
Find these in your own past-paper booklets for extra timed practice. Items above are written in the style of these papers; any adapted from a specific question say so.