What are the main differences between acids and bases in terms of their properties?

In the context of the IB MYP Science curriculum, acids and bases are distinguished by their chemical properties. Acids typically have a sour taste, can turn blue litmus paper red, and react with metals to produce hydrogen gas. They have a pH less than 7. Bases, on the other hand, have a bitter taste, feel slippery, can turn red litmus paper blue, and have a pH greater than 7. Both acids and bases can conduct electricity when dissolved in water due to the presence of ions.

How do acids and bases react to form salts?

In chemical reactions, acids and bases can react with each other in a process called neutralization. During this reaction, the hydrogen ions (H⁺) from the acid combine with the hydroxide ions (OH⁻) from the base to form water (H₂O). The remaining ions from the acid and base form a salt. For example, when hydrochloric acid (HCl) reacts with sodium hydroxide (NaOH), the products are water and sodium chloride (NaCl), which is a common table salt.

What is the role of pH in determining the strength of an acid or base?

The pH scale, which ranges from 0 to 14, is used to measure the acidity or alkalinity of a solution. In the IB MYP Science curriculum, understanding pH is crucial for determining the strength of acids and bases. A pH less than 7 indicates an acidic solution, with lower values representing stronger acids. A pH greater than 7 indicates a basic solution, with higher values representing stronger bases. A pH of 7 is considered neutral, which is the pH of pure water.

Why are indicators used in experiments involving acids and bases?

Indicators are substances used in science experiments to determine the acidity or basicity of a solution. They change color at specific pH levels, providing a visual representation of the solution's pH. Common indicators include litmus paper, phenolphthalein, and bromothymol blue. In the IB MYP curriculum, using indicators helps students understand the concept of pH and the properties of acids and bases through hands-on experiments.

Can you explain the concept of a buffer solution in relation to acids and bases?

A buffer solution is a special type of solution that resists changes in pH when small amounts of an acid or base are added. It is typically made from a weak acid and its conjugate base or a weak base and its conjugate acid. In the IB MYP Science curriculum, buffer solutions are important for maintaining stable pH levels in various chemical and biological processes. For example, the human body uses buffer systems to maintain the pH of blood, which is crucial for proper physiological function.

Why is "Treating 'base' and 'alkali' as identical." a common mistake in Acids, Bases and Salt?

Why it happens: Many alkalis are bases, and vice versa. How to avoid it: All alkalis are bases (they accept H⁺). NOT all bases are alkalis — copper oxide is a base but doesn't dissolve in water.

Why is "Thinking pH 4 is only twice as acidic as pH 8." a common mistake in Acids, Bases and Salt?

Why it happens: It looks linear. How to avoid it: Each pH unit is a 10× change. pH 4 is 10 000× more acidic than pH 8.

Why is "Forgetting that acid + metal produces hydrogen." a common mistake in Acids, Bases and Salt?

Why it happens: It's easy to confuse with acid + carbonate (CO₂). How to avoid it: Memorise the three products: metal → H₂, base → water only, carbonate → water + CO₂.

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Acids, Bases and Salts — IB MYP Sciences: pH, neutralisation and how salts form

Acids in your stomach, bases in cleaning products, salts in your food — chemistry shapes everyday life. This MYP Sciences note covers the pH scale, what makes an acid or a base, common neutralisation reactions, and how salts are made.

At a glance

Acids release H⁺ ions in water (e.g. HCl → H⁺ + Cl⁻).
Bases accept H⁺ ions; alkalis are bases that dissolve in water and release OH⁻.
pH scale 0-14: <7 acidic, 7 neutral, >7 alkaline.
Each pH step = 10× change in H⁺ concentration.
Universal indicator: red→orange→yellow (acid), green (neutral), blue→purple (alkali).
Neutralisation: acid + alkali → salt + water (H⁺ + OH⁻ → H₂O).
Acid + metal → salt + hydrogen.
Acid + carbonate → salt + water + CO₂.
A salt forms when the H of an acid is replaced by a metal (or ammonium).

What you’ll learn

Mapped to the IB MYP Sciences subject guide (2026 onwards).

MYP Sciences A — Define acids, bases and alkalis using ion language.
MYP Sciences A — Use the pH scale to classify a solution.
MYP Sciences A — Write word equations for acid + metal, acid + base, acid + carbonate.
MYP Sciences B — Plan a titration to find the concentration of an acid.
MYP Sciences D — Evaluate everyday neutralisation (indigestion remedies, acidic soil).

Acids, bases and the pH scale

Acids release H⁺; alkalis release OH⁻; pH measures how acidic or alkaline a solution is.

An acid is a substance that, when dissolved in water, releases H⁺ ions (protons). A base is a substance that accepts H⁺ ions. A soluble base is called an alkali — it releases OH⁻ ions in water.

The pH scale is a numerical measure of acidity:

pH	Class	Examples
0-1	Strongly acidic	Concentrated HCl, battery acid
2-3	Acidic	Lemon juice, vinegar
5-6	Weakly acidic	Coffee, milk
7	Neutral	Pure water
8-9	Weakly alkaline	Sea water, baking soda solution
10-13	Alkaline	Ammonia, soap
14	Strongly alkaline	Concentrated NaOH

Three key reactions of acids

Acid + metal, acid + base, acid + carbonate — all produce a salt.

1. Acid + metal → salt + hydrogen

$\text{Mg} + 2\text{HCl} \rightarrow \text{MgCl}_2 + \text{H}_2$

How salts form and how they're named

Replace the H of an acid with a metal: that's a salt.

A salt is what you get when the hydrogen in an acid is replaced by a metal (or by ammonium, NH₄⁺). Each common acid gives a particular family of salts:

Acid	Salt family	Example
HCl (hydrochloric)	chlorides	NaCl, MgCl₂
H₂SO₄ (sulfuric)	sulfates	Na₂SO₄, CuSO₄
HNO₃ (nitric)	nitrates	KNO₃, NaNO₃
CH₃COOH (ethanoic)	ethanoates	Na ethanoate

Worked example. Predict the salt formed when sulfuric acid reacts with sodium hydroxide.

H₂SO₄ + 2 NaOH → Na₂SO₄ + 2 H₂O. The salt is sodium sulfate (Na₂SO₄).

Many salts are useful in everyday life: NaCl (food), CaSO₄ (plaster of Paris), KNO₃ (fertiliser), NH₄NO₃ (fertiliser, explosive precursor).

Salt = H of acid replaced by metal.
HCl → chlorides; H₂SO₄ → sulfates; HNO₃ → nitrates.
Salts are everywhere: food, agriculture, construction.

Quick recap

Acid → H⁺ in water; alkali → OH⁻; pH 0-14.
Each pH step = 10× change in H⁺.
Acid + metal → salt + H₂ (pops with splint).
Acid + base → salt + water (neutralisation).
Acid + carbonate → salt + water + CO₂ (fizz; turns limewater milky).
Salt = H of acid replaced by metal.

Memorise this

Verbatim phrases and definitions MYP criterion-A markschemes credit.

pH < 7 acid, = 7 neutral, > 7 alkali
Acid + metal → salt + H₂
Acid + alkali → salt + water
Acid + carbonate → salt + water + CO₂
HCl → chlorides, H₂SO₄ → sulfates, HNO₃ → nitrates

How it’s examined

Criterion A tests pH classification, word equations and reaction products. Criterion B/C: titrations and salt preparation IAs. Criterion D may ask about indigestion, soil treatment or acid rain.

Sources: IB MYP Sciences guide (IBO, official subject guide). Last reviewed 2026-05-25.

Acids, Bases and Salt – Study Notes & Past Paper Style Questions | IB MYP Sciences (Years 1-5) | Tutopiya

Acids, Bases and Salt

Detailed Study Notes

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Acids, Bases and Salt — frequently asked questions

Acids, Bases and Salts — IB MYP Sciences: pH, neutralisation and how salts form

At a glance

What you’ll learn

Acids, bases and the pH scale

Three key reactions of acids

How salts form and how they're named

Quick recap

Memorise this

How it’s examined

Step-by-step worked examples — Acids, Bases and Salt

1Classifying solutions

2Acid + metal

3Naming salts

4Identifying a carbonate

Key Formulae — Acids, Bases and Salt

Neutralisation

Key Definitions and Keywords — Acids, Bases and Salt

Acid

Base

Alkali

pH

Neutralisation

Salt

Universal indicator

Common Mistakes and Misconceptions — Acids, Bases and Salt

✕Treating 'base' and 'alkali' as identical.

✕Thinking pH 4 is only twice as acidic as pH 8.

✕Forgetting that acid + metal produces hydrogen.