An alkali is a base that dissolves in water to produce hydroxide ions (OH - ). Alkalis have a pH above 7 and can neutralise acids to form a salt and water.

An acid reacts with a metal above hydrogen in the reactivity series to produce a ______ and ______ gas.

An acid reacts with a metal above hydrogen in the reactivity series to produce a salt and hydrogen gas.

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

The products are a salt , carbon dioxide and water . For example, hydrochloric acid and calcium carbonate produce calcium chloride, carbon dioxide and water.

Litmus paper turns ______ in acidic conditions and ______ in alkaline conditions.

Litmus paper turns red in acidic conditions and blue in alkaline conditions.

True or False? Litmus is a suitable indicator to use in acid-alkali titrations.

False. Litmus is not suitable for titrations because its colour change at the endpoint is not sharp and it passes through a purple transition colour in neutral solutions, making the endpoint difficult to detect.

Methyl orange turns ______ in acidic conditions and ______ in alkaline conditions.

Methyl orange turns red in acidic conditions and yellow in alkaline conditions.

How is the ammonium ion (NH 4 + ) identified in the laboratory?

The ammonium ion is identified by adding an alkali (such as NaOH) and warming gently. Ammonia gas (NH 3 ) is released, which turns damp red litmus paper blue.

To compare the relative acidity and alkalinity of solutions, ______ indicator is used and its colour is compared to a ______ .

To compare the relative acidity and alkalinity of solutions, universal indicator is used and its colour is compared to a pH colour chart .

True or False? Universal indicator is suitable for use in acid-alkali titrations.

False. Universal indicator shows a variety of colours across the pH range, making it difficult to determine a precise endpoint.

An acid produces ______ ions in water, making the solution acidic. An alkali produces ______ ions in water, making the solution alkaline.

An acid produces hydrogen ions in water, making the solution acidic. An alkali produces hydroxide ions in water, making the solution alkaline.

What is the ionic equation for the neutralisation of an acid by an alkali?

The ionic equation is: H + (aq) + OH - (aq) → H 2 O (l)

On the pH scale, solutions with a pH below 7 are ______ , pH 7 is ______ and pH above 7 are ______ .

On the pH scale, solutions with a pH below 7 are acidic , pH 7 is neutral and pH above 7 are alkaline .

True or False? When magnesium reacts with hydrochloric acid, a neutralisation reaction occurs.

False. Neutralisation requires an acid and a base to form salt and water. The reaction of magnesium with HCl produces magnesium chloride and hydrogen gas, but no water, so it is not a neutralisation reaction.

A lower pH indicates a ______ concentration of H + ions. A solution of pH 3 has ______ times the H + concentration of a solution of pH 4.

A lower pH indicates a higher concentration of H + ions. A solution of pH 3 has ten times the H + concentration of a solution of pH 4.

What does it mean that the pH scale is logarithmic?

Each change of 1 unit on the pH scale represents a change in H + concentration by a factor of 10. For example, a pH 2 solution has 100 times the H + concentration of a pH 4 solution.

Why can aqueous acid solutions conduct electricity?

Aqueous acid solutions conduct electricity because they contain mobile ions — the H + ions and the acid's anion (e.g. Cl - in HCl) — that are free to move and carry charge through the solution.

What is an acid in terms of proton transfer?

An acid is a proton donor : it ionises in water to release H + ions (protons) into solution.

A ______ acid completely dissociates in water, producing a high concentration of H + ions and a very low pH.

A strong acid completely dissociates in water, producing a high concentration of H + ions and a very low pH.

True or False? A base is a proton donor.

False. A base is a proton acceptor : it accepts the H + ions (protons) donated by an acid.

For a weak acid, the dissociation equilibrium lies to the ______ , meaning there is a ______ concentration of H + ions compared to a strong acid of the same concentration.

For a weak acid, the dissociation equilibrium lies to the left , meaning there is a lower concentration of H + ions compared to a strong acid of the same concentration.

What is the difference between a strong acid and a concentrated acid?

Strength and concentration are different properties: Strength describes how completely an acid dissociates Concentration describes how many moles per dm 3 are present. A strong acid at low concentration can be more acidic than a weak acid at high concentration.

In the equation HCl (aq) → H + (aq) + Cl - (aq), the single arrow shows the dissociation is ______ . For weak acids, a ______ arrow (⇌) is used instead.

In the equation HCl (aq) → H + (aq) + Cl - (aq), the single arrow shows the dissociation is complete . For weak acids, a reversible arrow (⇌) is used instead.

Write the equilibrium equation for the partial dissociation of ethanoic acid (CH 3 COOH) in water.

The equilibrium equation for the partial dissociation of ethanoic acid (CH 3 COOH) in water is : CH 3 COOH (aq) ⇌ H + (aq) + CH 3 COO - (aq) The equilibrium lies to the left, meaning most molecules remain undissociated.

O LevelChemistryCambridge (CIE)Flashcards7. Acids, Bases & Salts7.1 The Characteristic Properties of Acids & Bases

7.1 The Characteristic Properties of Acids & Bases (Cambridge (CIE) O Level Chemistry): Flashcards

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FrontProperties of Acids & Bases
What is an alkali?

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What is an alkali?
An alkali is a base that dissolves in water to produce hydroxide ions (OH^-). Alkalis have a pH above 7 and can neutralise acids to form a salt and water.
An acid reacts with a metal above hydrogen in the reactivity series to produce a ______ and ______ gas.
An acid reacts with a metal above hydrogen in the reactivity series to produce a salt and hydrogen gas.
What are the products when an acid reacts with a metal carbonate?
The products are a salt, carbon dioxide and water. For example, hydrochloric acid and calcium carbonate produce calcium chloride, carbon dioxide and water.
Litmus paper turns ______ in acidic conditions and ______ in alkaline conditions.
Litmus paper turns red in acidic conditions and blue in alkaline conditions.
True or False?
Litmus is a suitable indicator to use in acid-alkali titrations.
False.
Litmus is not suitable for titrations because its colour change at the endpoint is not sharp and it passes through a purple transition colour in neutral solutions, making the endpoint difficult to detect.
Methyl orange turns ______ in acidic conditions and ______ in alkaline conditions.
Methyl orange turns red in acidic conditions and yellow in alkaline conditions.
How is the ammonium ion (NH₄⁺) identified in the laboratory?
The ammonium ion is identified by adding an alkali (such as NaOH) and warming gently. Ammonia gas (NH₃) is released, which turns damp red litmus paper blue.
To compare the relative acidity and alkalinity of solutions, ______ indicator is used and its colour is compared to a ______.
To compare the relative acidity and alkalinity of solutions, universal indicator is used and its colour is compared to a pH colour chart.
True or False?
Universal indicator is suitable for use in acid-alkali titrations.
False.
Universal indicator shows a variety of colours across the pH range, making it difficult to determine a precise endpoint.
An acid produces ______ ions in water, making the solution acidic.
An alkali produces ______ ions in water, making the solution alkaline.
An acid produces hydrogen ions in water, making the solution acidic.
An alkali produces hydroxide ions in water, making the solution alkaline.
What is the ionic equation for the neutralisation of an acid by an alkali?
The ionic equation is: H⁺ (aq) + OH^- (aq) → H₂O (l)
On the pH scale, solutions with a pH below 7 are ______, pH 7 is ______ and pH above 7 are ______.
On the pH scale, solutions with a pH below 7 are acidic, pH 7 is neutral and pH above 7 are alkaline.
True or False?
When magnesium reacts with hydrochloric acid, a neutralisation reaction occurs.
False.
Neutralisation requires an acid and a base to form salt and water. The reaction of magnesium with HCl produces magnesium chloride and hydrogen gas, but no water, so it is not a neutralisation reaction.
A lower pH indicates a ______ concentration of H⁺ ions. A solution of pH 3 has ______ times the H⁺ concentration of a solution of pH 4.
A lower pH indicates a higher concentration of H⁺ ions. A solution of pH 3 has ten times the H⁺ concentration of a solution of pH 4.
What does it mean that the pH scale is logarithmic?
Each change of 1 unit on the pH scale represents a change in H⁺ concentration by a factor of 10. For example, a pH 2 solution has 100 times the H⁺ concentration of a pH 4 solution.
Why can aqueous acid solutions conduct electricity?
Aqueous acid solutions conduct electricity because they contain mobile ions — the H⁺ ions and the acid's anion (e.g. Cl^- in HCl) — that are free to move and carry charge through the solution.
What is an acid in terms of proton transfer?
An acid is a proton donor: it ionises in water to release H⁺ ions (protons) into solution.
A ______ acid completely dissociates in water, producing a high concentration of H⁺ ions and a very low pH.
A strong acid completely dissociates in water, producing a high concentration of H⁺ ions and a very low pH.
True or False?
A base is a proton donor.
False.
A base is a proton acceptor: it accepts the H⁺ ions (protons) donated by an acid.
For a weak acid, the dissociation equilibrium lies to the ______, meaning there is a ______ concentration of H⁺ ions compared to a strong acid of the same concentration.
For a weak acid, the dissociation equilibrium lies to the left, meaning there is a lower concentration of H⁺ ions compared to a strong acid of the same concentration.
What is the difference between a strong acid and a concentrated acid?
Strength and concentration are different properties:
- Strength describes how completely an acid dissociates
- Concentration describes how many moles per dm³ are present.
A strong acid at low concentration can be more acidic than a weak acid at high concentration.
In the equation HCl (aq) → H⁺ (aq) + Cl^- (aq), the single arrow shows the dissociation is ______. For weak acids, a ______ arrow (⇌) is used instead.
In the equation HCl (aq) → H⁺ (aq) + Cl^- (aq), the single arrow shows the dissociation is complete. For weak acids, a reversible arrow (⇌) is used instead.
Write the equilibrium equation for the partial dissociation of ethanoic acid (CH₃COOH) in water.
The equilibrium equation for the partial dissociation of ethanoic acid (CH₃COOH) in water is :
CH₃COOH (aq) ⇌ H⁺ (aq) + CH₃COO^- (aq)
The equilibrium lies to the left, meaning most molecules remain undissociated.

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