The Characteristic Properties Of Acids And Bases

Learn it by playing

Answer these questions to earn energy, then fish and explore. No account needed.

For teachers: ready-to-use lesson slides, revision notes, diagrams for The Characteristic Properties Of Acids And Bases (Co-ordinated Sciences (Double Award) [CIE], Chemistry) — use them in your lesson, or run the topic as a live class game.

Notes

Properties of Acids

Acids have $pH < 7$ , sour taste (if edible), and are corrosive.
Acids neutralise bases to form a salt and water.
In water, acids release **hydrogen ions (H⁺)**; e.g., HCl → H⁺ + Cl⁻.
Acids react with metals (above H in reactivity series) to give salt + H₂.
Acids react with metal oxides/hydroxides (bases) to give salt + water (neutralisation).
Acids react with metal carbonates to give salt + CO₂ + H₂O.

Properties of Bases & Alkalis

Bases have $pH >$ 7; a water‑soluble base is an **alkali**.
Bases neutralise acids to form a salt and water.
In water, alkalis release **hydroxide ions (OH⁻)**; e.g., NaOH → Na⁺ + OH⁻.
Bases are usually metal oxides or hydroxides.
Alkalis react with ammonium salts (e.g., NH₄Cl) to give salt + water + NH₃ (test: damp red litmus turns blue).

Indicators

**Litmus**: red in acid, blue in alkali (not sharp for titrations).
**Methyl orange**: red in acid, yellow in alkali.
**Thymolphthalein**: colourless in acid, blue in alkali.
**Universal indicator**: mixture of dyes giving a colour range for pH 1–14.

Neutralisation & Ions

Neutralisation: H⁺ + OH⁻ → H₂O (net ionic equation).
Acids are sources of H⁺; alkalis are sources of OH⁻.
Not all acid reactions are neutralisations (e.g., acid + metal produces no water).
The pH scale is logarithmic: a change of 1 pH unit $= \times 10$ change in [H⁺].

pH Scale & Hydrogen Ion Concentration

pH 0–2: strong acid; pH 3–6: weak acid; pH 7: neutral.
pH 8–11: weak alkali; pH 12–14: strong alkali.
Lower $pH =$ higher [H⁺]; higher $pH =$ higher [OH⁻].
Universal indicator gives approximate pH by matching colour to a chart.

Classifying Oxides

**Acidic oxides** (non‑metal + O): react with bases to form salt + water; produce acidic solutions (e.g., CO₂, SO₂).
**Basic oxides** $(metal + O)$ : react with acids to form salt + water; produce alkaline solutions (e.g., CuO, CaO).
**Amphoteric oxides** (e.g., ZnO, Al₂O₃): react with both acids and bases to give salt + water.
**Neutral oxides** (e.g., N₂O, NO, CO): do not react with acids or bases.

Particle arrangement in solid, liquid and gas states (not directly about acids but useful for understanding solutions).

Practice questions

Free preview — 8 of 12 questions. Sign up to see them all.

1.All bases are soluble in water and are called alkalis.
Easy
True or false?
2.Which of the following is the correct net ionic equation for the neutralisation of an acid by a base?
Easy
- AH⁺(aq) + OH⁻(aq) → H₂O(l)
- BH⁺(aq) + OH⁻(aq) → H₂O₂(l)
- CH⁺(aq) + O²⁻(aq) → H₂O(l)
- DH₂O(l) → H⁺(aq) + OH⁻(aq)
3.State the colour of litmus in an alkali.
Easy
4.Complete the sentence about the reaction of acids with metals.
Medium
When an acid reacts with a metal, the products are $a ____ and$ hydrogen gas.
5.A solution has a pH of 3. How many times greater is the hydrogen ion concentration compared to a solution of pH 5?
Medium
- A100
- B120
- C90
- D110
6.Match each oxide to its classification.
Medium
- CO₂
- MgO
- Al₂O₃
- Acidic oxide
- Basic oxide
- Amphoteric oxide
7.Name the gas produced when an acid reacts with a metal carbonate.
Medium
8.Which indicator is most suitable for determining the endpoint in an acid-alkali titration?
Medium
- ALitmus
- BMethyl orange
- CThymolphthalein
- DUniversal indicator

Slides

Properties of Acids

Acids have pH values below 7, taste sour (when edible), and are corrosive.
Acids neutralise bases to form a salt and water.
In water, acids produce hydrogen ions (H⁺), which make the solution acidic.

Which ion is responsible for the acidic properties of a solution?

OH⁻
H⁺
Cl⁻
Na⁺

Reactions of Acids with Metals

Only metals above hydrogen in the reactivity series react with dilute acids.
The products are a salt and hydrogen gas: acid + metal → salt + hydrogen.
The salt name depends on the acid used (e.g., hydrochloric acid gives a chloride).

When magnesium reacts with dilute hydrochloric acid, the products are magnesium $____ and ____ gas$ .

Reactions of Acids with Bases and Carbonates

Acids neutralise bases (metal oxides/hydroxides) to form salt and water.
Acids react with metal carbonates to form salt, carbon dioxide, and water.
Example: MgCO₃ + 2HCl → MgCl₂ + CO₂ + H₂O.

What are the products when hydrochloric acid reacts with calcium carbonate?

Calcium chloride and water only
Calcium chloride, carbon dioxide, and water
Calcium oxide and hydrogen
Calcium and chlorine

Indicators

Indicators change colour in acids and alkalis.
Litmus: red in acid, blue in alkali.
Methyl orange: red in acid, yellow in alkali.
Thymolphthalein: colourless in acid, blue in alkali.

Which of these are true about indicators?

Litmus turns blue in acidic solutions.
Methyl orange is red in acid and yellow in alkali.
Thymolphthalein is colourless in acid.
Litmus is suitable for titrations due to its sharp colour change.

Properties of Bases and Alkalis

Bases have pH above 7; water-soluble bases are called alkalis.
Alkalis produce hydroxide ions (OH⁻) in water.
Bases neutralise acids to form salt and water.

Which ion is responsible for the alkaline properties of a solution?

H⁺
OH⁻
Cl⁻
Na⁺

Neutralisation and the Ionic Equation

Neutralisation is the reaction between H⁺ from acids and OH⁻ from alkalis.
The net ionic equation is: H⁺(aq) + OH⁻(aq) → H₂O(l).
Not all acid reactions are neutralisations (e.g., acid + metal produces no water).

The net ionic equation for neutralisation is H⁺ + ____ → ____.

pH Scale and Hydrogen Ion Concentration

pH scale runs from 0 to 14; acids $<7$ , alkalis $>7$ , neutral $=7$ .
Lower pH means higher H⁺ concentration (stronger acid).
The scale is logarithmic: a change of 1 pH unit means a tenfold change in H⁺ concentration.

How many times more concentrated in H⁺ is a solution of pH 3 compared to pH 5?

2 times
10 times
100 times
1000 times

Classifying Oxides

Acidic oxides: formed by non-metals, react with bases to form salt and water, produce acidic solutions (e.g., CO₂, SO₂).
Basic oxides: formed by metals, react with acids to form salt and water, produce alkaline solutions (e.g., CuO, CaO).
Amphoteric oxides: can act as both acid and base (e.g., ZnO, Al₂O₃).
Neutral oxides: do not react with acids or bases (e.g., N₂O, CO).

Which of these are true about oxides?

Non-metals form basic oxides.
Basic oxides react with acids to form salt and water.
Aluminium oxide is amphoteric.
Carbon monoxide is a neutral oxide.

Alkalis and Ammonium Salts

Ammonium salts react with alkalis when warmed to produce ammonia gas, water, and a salt.
Example: NH₄Cl + NaOH → NaCl + H₂O + NH₃.
Ammonia turns damp red litmus paper blue, confirming the ammonium ion.

What gas is produced when an ammonium salt is warmed with an alkali?

Hydrogen
Oxygen
Ammonia
Carbon dioxide

Flashcards

What is the pH range of acids?

Acids have pH values below 7.

What ions do acids produce when added to water?

Acids produce hydrogen ions (H+).

What is the general equation for the reaction of an acid with a metal?

acid + metal → salt + hydrogen

What is the general equation for the reaction of an acid with a base?

acid + base → salt + water

What are the products when an acid reacts with a metal carbonate?

salt + carbon dioxide + water

What is the colour of litmus in acid and in alkali?

Litmus is red in acid and blue in alkali.

What is the colour of methyl orange in acid and in alkali?

Methyl orange is red in acid and yellow in alkali.

What is the colour of thymolphthalein in acid and in alkali?

Thymolphthalein is colourless in acid and blue in alkali.

What is the pH range of bases?

Bases have pH values above 7.

What ions do alkalis produce when added to water?

Alkalis produce hydroxide ions (OH-).

What is the net ionic equation for neutralisation?

$H+(aq) + OH-(aq)$ → H2O(l)

What is the pH of a neutral solution?

pH 7

How many times more concentrated in H+ is a pH 3 acid compared to a pH 4 acid?

10 times more concentrated.

What is universal indicator used for?

To measure the pH of a solution by matching the colour to a pH colour chart.

What type of oxide is formed when a non-metal combines with oxygen?

Acidic oxide

What type of oxide is formed when a metal combines with oxygen?

Basic oxide

Give an example of an acidic oxide.

Carbon dioxide (CO2), sulfur dioxide (SO2), nitrogen dioxide (NO2), or silicon dioxide (SiO2).

Give an example of a basic oxide.

Copper(II) oxide (CuO) or calcium oxide (CaO).

What are amphoteric oxides?

Oxides that can behave as both acidic and basic, reacting with both acids and bases to form salt and water.

Give two examples of amphoteric oxides.

Zinc oxide (ZnO) and aluminium oxide (Al2O3).

What are neutral oxides?

Oxides that do not react with either acids or bases, e.g., N2O, NO, and CO.

What happens when an alkali is warmed with an ammonium salt?

A salt, water, and ammonia gas are produced; ammonia turns damp red litmus paper blue.

Why is litmus not suitable for titrations?

Because its colour change is not sharp and it goes through a purple transition colour in neutral solutions, making it difficult to determine the endpoint.

Unlock all 12 questions, slides, flashcards & more

Create a free account to see every question, the slides, flashcards and revision notes for this topic.

Past papers

Past-paper practice for this topic is coming soon.

🗂️ Coming soon