DSE Chemistry | Acid-base neutralisation and titration: a tutor lesson guide

DSE Chemistry | Acid-base neutralisation and titration: a tutor lesson guide | From moles to the curve

2026-11-04

Tutor lesson-prep guides · Secondary Chemistry

Students can write acid plus base gives salt plus water, then multiply two concentrations and call it moles, or forget that sulfuric acid brings two hydrogen ions. This lesson drills one sentence: moles first, volume second. It starts from 25.0 cm3 of 0.100 M sodium hydroxide and lets students find the 25.0 cm3 end point themselves.

Objectives — Students can: (1) compute the titre from moles equal to concentration times volume, including the factor for a diprotic acid; (2) explain that neutralisation is hydrogen ions meeting hydroxide ions, and name where the salt and water come from; (3) choose a suitable indicator and state the direction of a reading error.

01 Prerequisites (3-minute check)

If any of these fails, fix it before the lesson starts.

Skill	Quick check	Pass mark
The mole	How many particles are in one mole?	6.02 times ten to the twenty-three
Molarity	What does 0.100 M mean?	0.100 mole of solute per cubic decimetre
Unit conversion	25.0 cm3 in dm3?	0.0250 dm3

02 Lesson flow (60 minutes)

Time	Stage	Tutor does	Student does
0-8 min	Three-question check	Mole, molarity, volume conversion	Answer orally
8-22 min	Nature of neutralisation	H plus OH gives water, ionic equation	Write the net ionic equation
22-38 min	Mole stoichiometry	25.0 cm3 of 0.100 M sodium hydroxide	Find the acid volume
38-50 min	Curve and error	End point, equivalence point, indicator	State the error direction
50-56 min	Timed practice	Two calculations and one explanation	Work alone
56-60 min	Exit check	Three checkpoints, one question each	Self-assess and mark gaps

03 Teaching script (read it out)

Scene 1: Neutralisation: hydrogen ions move, nothing else

Write the net ionic equation first and delete the spectator ions, so only hydrogen and hydroxide remain on the left. Two consequences follow: the enthalpy change is nearly constant, and the stoichiometry counts hydrogen and hydroxide ions only, whatever the strength of the acid. Students should say plainly that the salt is not a by-product but the leftover spectator ions coming together in solution.

Students delete spectators, write the net ionic equation and check each other.

Scene 2: Mole stoichiometry: moles first, volume second

25.0 cm3 of 0.100 M sodium hydroxide carries 2.50 millimoles of hydroxide, so 0.100 M hydrochloric acid needs 25.0 cm3 because the ratio is one to one. Switch to 0.0500 M sulfuric acid and everything changes: each unit supplies two hydrogen ions, so only 1.25 millimoles are needed and the volume stays at 25.0 cm3. The two equal volumes are deliberate: equal volume does not mean equal moles.

Students write the mole ratio first, substitute second, add units last.

Scene 3: End point and error: the direction of one drop

An indicator changes colour near the equivalence point, but the eye usually overshoots by half a drop to a drop. Against 25.0 cm3, an extra 0.10 cm3 is 0.4 per cent, and the calculated acid concentration comes out high because extra acid was used. Train one habit: state high or low, then why. Rinsing the conical flask with distilled water dilutes the base, so less acid is needed and the result comes out low.

In pairs, students give the direction for three procedural mistakes.

04 Question types and worked steps

Type	Example	Steps	Answer
Monoprotic calculation	25.0 cm3 of 0.100 M hydroxide with 0.100 M acid	Find moles, use the one to one ratio, divide by concentration	25.0 cm3
Diprotic calculation	Same base with 0.0500 M sulfuric acid	Halve the moles, then divide by concentration	25.0 cm3
Indicator choice	Strong acid into strong base: which indicator?	Equivalence near pH 7, so phenolphthalein or methyl orange	State the pH range
Error direction	Flask rinsed with distilled water	Base diluted, less acid needed, result low	Direction plus reason

Sanity check (teach this): The three numbers must close: 2.50 millimoles of base against 25.0 cm3 of 0.100 M acid returns exactly 2.50 when multiplied. For sulfuric acid the moles halve and the concentration halves, so the volume does not move; that is the one line students suspect is a mistake. 0.100 M sodium hydroxide is 4.00 grams per cubic decimetre, so an answer of 0.1 grams forgets the molar mass. An error of 0.4 per cent is under one per cent, so report three significant figures.

05 Independent practice (3 questions)

Question	Answer	What to watch
20.0 cm3 of 0.150 M hydroxide with 0.100 M acid: volume	30.0 cm3	Start from 3.00 millimoles
Same base with 0.100 M sulfuric acid	15.0 cm3	Remember to halve
Explain why rinsing the flask with water does not change the result	The moles of base stay the same	Say moles, not concentration

06 Common mistakes and what to say

Mistake	Student writes	Say this
Multiplying concentrations and calling it moles	Writes 0.100 times 0.100 as the answer	Ask for the unit; moles always need a volume.
Forgetting the diprotic factor	Gives 25.0 cm3 for sulfuric acid	Write the hydrogen count, then the mole ratio, then substitute.
Confusing end point with equivalence point	Says colour change means pH 7	Phenolphthalein turns near pH 8.2, so the end point only approximates it.
Reporting an error without direction	Writes there will be some error	Demand the pattern: high or low, because this quantity grew or shrank.

07 Homework (paper, section and question numbers)

Chemistry chapter index — All chapters
Chemistry practice papers — Acids: calculation questions 2 and 4, error question 1

08 Exit check (last 5 minutes)

Question	Answer	Decision
Moles	How many millimoles in 25.0 cm3 of 0.100 M base?	Says 0.1: forgot the volume
Diprotic	Why does the sulfuric acid volume stay the same?	Says the concentration is lower: name the hydrogen count
Error direction	Flask rinsed with water: high, low or unchanged?	Says unchanged: ask which vessel was rinsed

09 Tutor FAQ

Is phenolphthalein always the right indicator?

No; match it to the equivalence pH, methyl orange for strong acid with weak base.

Why repeat a titration?

Average two or three concordant readings to cut random error, not to look tidy.

How do molarity and mass concentration relate?

Multiply by molar mass, so 0.100 M sodium hydroxide is 4.00 grams per dm3.

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A TutorZone lesson-prep guide. Written by the TutorZone team; questions and lesson flow are original and are not taken from any school or publisher material.