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MYP Chemistry: Neutralisation Reactions FAQ
Answered by RevisionPrep's IB Educators
Neutralisation trips up more MYP 4-5 students than almost any other acids-and-bases topic — usually because they memorise the word equation but can't apply it to a new salt. Here's what actually matters for your assessments, answered directly, with worked examples where they help.
The Concept
What is neutralisation reactions in MYP Chemistry?
A neutralisation reaction is when an acid reacts with a base (or alkali) to produce a salt and water, cancelling out the acidic and basic properties of both. The general word equation is: acid + base → salt + water. If the base is a carbonate, you also get carbon dioxide gas.
Two versions you need to know:
- Acid + metal hydroxide → salt + water
- Acid + metal carbonate → salt + water + carbon dioxide
Example: hydrochloric acid + sodium hydroxide → sodium chloride + water. In symbols: HCl + NaOH → NaCl + H₂O. Notice it's a 1:1 ratio here — that won't always be true, which is the mistake most students make.
Why does neutralisation produce a salt and water?
Because the H⁺ ions from the acid combine with the OH⁻ ions from the base to form water (H₂O), while the leftover metal ion and non-metal ion pair up to form the salt. It's genuinely an ion-swap, not a mysterious 'cancelling out' — I always draw the ions separately on the board before combining them.
Think of it as two couples swapping partners: H⁺ pairs with OH⁻ to make water, and the metal cation pairs with the acid's remaining anion to make the salt. This is why the salt named always matches the acid used — hydrochloric acid gives chloride salts, sulfuric acid gives sulfate salts, nitric acid gives nitrate salts.
How do you name the salt formed in a neutralisation reaction?
The salt's name comes from two parts: the metal (or ammonium) from the base, and the acid's ion name — chloride for hydrochloric acid, sulfate for sulfuric acid, nitrate for nitric acid. Sodium hydroxide plus hydrochloric acid gives sodium chloride; potassium hydroxide plus sulfuric acid gives potassium sulfate.
Quick reference:
| Acid | Salt ending |
|---|---|
| Hydrochloric acid | -chloride |
| Sulfuric acid | -sulfate |
| Nitric acid | -nitrate |
| Carbonic/ethanoic acid | -carbonate/-ethanoate |
Common mistake: writing 'sodium hydrochloride' — the acid's -ic acid ending never carries over into the salt name.
Applying It: Equations & Calculations
How do you write and balance a neutralisation equation?
Start with the word equation, write the correct chemical formulae for each substance, then balance atoms one element at a time — usually hydrogen and oxygen last since they appear in water. Always check charges balance too: a 2+ metal ion needs two 1- ions to form a neutral salt.
Worked example: Sulfuric acid + sodium hydroxide.
- Word equation: sulfuric acid + sodium hydroxide → sodium sulfate + water
- Formulae: H₂SO₄ + NaOH → Na₂SO₄ + H₂O
- Balance Na: need 2NaOH
- Check H and O balance: H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O ✓
Quick tip: balance metals first, then the acid's anion group (SO₄, NO₃, CO₃ etc.) as one whole unit rather than splitting it into separate atoms — it saves time and errors.
How do you calculate the volume needed to neutralise an acid?
Use the mole relationship from your balanced equation together with , where is concentration in mol/dm³, is moles, and is volume in dm³. Work out moles of acid first, use the equation's ratio to find moles of base needed, then convert back to volume.
Worked example: How much 0.5 mol/dm³ NaOH is needed to neutralise 25 cm³ of 0.2 mol/dm³ HCl?
- Moles HCl = mol
- Ratio HCl:NaOH is 1:1, so moles NaOH = 0.005 mol
- dm³ = 10 cm³
This titration-style calculation shows up constantly in MYP Criterion C/D investigations, so it's worth practising until the steps feel automatic.
What experiment do MYP students usually do to investigate neutralisation?
Most schools run a titration: adding acid to an alkali (or vice versa) using a burette, with an indicator like phenolphthalein or universal indicator to spot the endpoint where the solution turns neutral. Some MYP units instead use a pH probe to track the change in real time rather than relying on colour.
3 things examiners look for in your write-up (Criterion B — Inquiring and Designing):
- A clearly stated, testable research question — not just 'find the neutralisation point'
- Identified variables: independent (volume added), dependent (pH or colour change), controlled (concentration, temperature)
- A method detailed enough that someone else could repeat it exactly
If you're using a data logger, record readings every 1-2 cm³ near the expected endpoint — that's where the pH curve is steepest and most easily missed.
Common Confusions
What's the difference between neutralisation and dilution?
Dilution just adds water to reduce concentration — the substance is still the same acid or base, only weaker. Neutralisation is a chemical reaction where an acid and base react to form entirely new substances, a salt and water, and the acid/base properties disappear. Diluting an acid still leaves you with an acid; neutralising it doesn't.
A quick check I give students: if you dilute hydrochloric acid, the pH rises slightly but stays below 7. If you neutralise it fully with sodium hydroxide, the pH reaches 7 and the product (sodium chloride solution) has none of the acid's reactive properties left — it won't react with magnesium ribbon, for instance.
Why doesn't the pH always end up at exactly 7 after neutralisation?
It depends on the salt formed. A strong acid plus a strong base (like HCl and NaOH) gives a neutral salt solution at pH 7. But a weak acid plus a strong base, or vice versa, produces a salt that's slightly acidic or alkaline in solution, so the endpoint sits above or below 7.
Ethanoic acid (a weak acid) reacting with sodium hydroxide gives sodium ethanoate, a salt that's mildly alkaline in solution because the ethanoate ion reacts slightly with water. This is a genuine step-up from the simple 'acid + base = pH 7' picture taught in MYP 1-3, and examiners reward students who can explain the exception, not just quote the rule.
How is neutralisation used in real life?
Farmers spread calcium hydroxide (lime) on acidic soil to neutralise it before planting. Indigestion tablets contain a weak base like magnesium hydroxide to neutralise excess stomach acid. Factories neutralise acidic waste water before releasing it, and dentists recommend fluoride toothpaste partly because it helps neutralise acids produced by mouth bacteria.
Common MYP exam application question: 'Explain why farmers add lime to acidic fields.' A strong answer names the base (calcium hydroxide or calcium oxide), states the word equation with the soil acid, and links it to crop yield — not just 'it makes the soil less acidic', which rarely earns full marks under Criterion A.
Assessment & Study Strategy
How is neutralisation assessed in MYP Chemistry?
Neutralisation typically appears under Criterion A (Knowing and Understanding) through equation-writing and calculation questions, and under Criteria B–D if it's the focus of a practical investigation. According to the MYP Sciences guide, assessment is criterion-referenced against command terms like 'state', 'explain' and 'deduce' rather than against a percentage mark.
A 'state' question just wants the word or symbol equation. An 'explain' question wants the mechanism — why H⁺ and OH⁻ combine, why the salt is named as it is. Losing marks on explain questions usually means writing a state-level answer, which is the single most common error I see marking MYP scripts.
What mistakes do students most often make with neutralisation questions?
The three recurring errors: forgetting to balance charge as well as atoms, mixing up the salt's name (e.g. writing 'sodium hydrochloride'), and stating pH always ends at exactly 7 regardless of which acid and base were used. Each one is fixable with focused practice rather than more general revision.
Checklist before you submit any neutralisation answer:
- Did I balance both sides for atoms AND overall charge?
- Does my salt name match the acid used (chloride/sulfate/nitrate)?
- Have I checked whether this is a strong-strong, strong-weak, or weak-strong pairing before assuming pH 7?
- Did the question ask me to 'state' or 'explain' — and did my answer match that command term?
How can I get top marks on neutralisation topics in MYP Chemistry?
Practise writing and balancing equations from word descriptions until it's automatic, learn the salt-naming pattern cold, and always link your answer back to particle-level behaviour (ions combining) rather than just quoting 'acid plus base equals salt plus water'. Examiners reward the explanation, not the memorised phrase.
On RevisionPrep, the MYP Chemistry Topical Worksheets isolate neutralisation equation-writing and titration calculations into short, focused problem sets, and the Revision Notes summarise the strong/weak acid-base pH exceptions in one table — useful for the week before a summative.
How can I help my child revise neutralisation reactions at home?
The fastest home check is asking your child to write and balance a neutralisation equation from a word description without notes — if they hesitate on the salt name or forget to balance charge, that's exactly where most marks are lost in MYP assessments. A quick weekly practice question keeps it fresh.
You don't need a chemistry background to help here. Ask them to explain out loud why the salt is named what it is, or to talk through a titration calculation step by step — teaching it back is one of the most reliable ways to spot a shaky understanding before a summative assessment.
Strong vs Weak Acid/Base Neutralisation: Resulting pH
| Acid type | Base type | Salt solution pH |
| Strong (HCl) | Strong (NaOH) | pH 7 (neutral) |
| Weak (ethanoic acid) | Strong (NaOH) | pH above 7 (mildly alkaline) |
| Strong (HCl) | Weak (ammonia) | pH below 7 (mildly acidic) |
For more worked equations, titration calculations and criterion-referenced practice questions on acids and bases, explore the MYP Chemistry Revision Notes and Topical Worksheets on RevisionPrep.