Grade 11 Physical Sciences · Chemical Change

Write acid-base reaction equations

Write equations for acids reacting with bases, oxides or carbonates, or with water (HCl + NaOH → NaCl + H₂O).

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Common Acid Base Reactions Grade 11Kevinmathscience

Grade 11 Acids and Bases: Type of reactions Introduction | Defining acids and basesMiss Martins Maths and Science

Neutralization ReactionsProfessor Dave Explains

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Question 1.7 · November 2025 · Paper 2 · National (DBE) · 2 marks

Various options are provided as possible answers to the following questions. Each question has only ONE correct answer.

1.7 The products for the reaction between a metal oxide and an acid are ...(2)

A a salt and water.
B a salt and hydrogen gas.
C a salt and carbon dioxide.
D a salt, water and carbon dioxide.

Work it out on paper first. Then mark yourself with the official memo, one tick at a time.

More past paper questions: write acid-base reaction equations

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3. Question 7.1.3 · May/June 2024 · Paper 2 · National (DBE) · 2 marks
7.1 A standard solution is prepared by dissolving 10 g of sodium carbonate, $Na_{2} CO_{3}$ (s), in $0, 7$ dm $^{3}$ of water.

Answer the questions that follow.
7.1.3 Write an equation that explains the answer to QUESTION 7.1.2.(2)
Show the memo (2 ticks)Memo
1. ✓
  Reactants $CO_{3}^{2 -} (aq) + H_{2} O (ℓ)$
  1 mark · Write acid-base reaction equations
2. ✓
  Products $⇌ HCO_{3}^{-} (aq) + OH^{-} (aq)$
  1 mark · Write acid-base reaction equations
4. Question 7.1.5 · November 2025 · Paper 2 · National (DBE) · 3 marks
7.1 Phosphoric acid, $H_{3} PO_{4}$ (aq), is an example of an acid that can ionise in three steps, as shown below.

$H_{3} PO_{4} (aq) + H_{2} O (ℓ) ⇌ H_{3} O^{+} (aq) + H_{2} PO_{4}^{-} (aq)$ $K_{a} = 6, 9 \times 1 0^{- 3}$
$H_{2} PO_{4}^{-} (aq) + H_{2} O (ℓ) ⇌ H_{3} O^{+} (aq) + HPO_{4}^{2 -} (aq)$ $K_{a} = 6, 2 \times 1 0^{- 8}$
$HPO_{4}^{2 -} (aq) + H_{2} O (ℓ) ⇌ H_{3} O^{+} (aq) + PO_{4}^{3 -} (aq)$ $K_{a} = 4, 8 \times 1 0^{- 13}$

Answer the questions that follow.
7.1.5 Write a balanced equation to explain the answer to QUESTION 7.1.4.(3)
Show the memo (3 ticks)Memo
1. ✓
  Reactants $HPO_{4}^{2 -} (aq) + H_{2} O (ℓ)$
  1 mark · Write acid-base reaction equations
2. ✓
  Products $H_{2} PO_{4}^{-} (aq) + OH^{-} (aq)$
  OR $H_{3} PO_{4} (aq) + 2 OH^{-} (aq)$
  1 mark · Write acid-base reaction equations
3. ✓
  Balancing $HPO_{4}^{2 -} (aq) + H_{2} O (ℓ) ⇌ H_{2} PO_{4}^{-} (aq) + OH^{-} (aq)$
  OR $HPO_{4}^{2 -} (aq) + 2 H_{2} O (ℓ) ⇌ H_{3} PO_{4} (aq) + 2 OH^{-} (aq)$
  1 mark · Balance a chemical equation
5. Question 7.2.4 · May/June 2023 · Paper 2 · National (DBE) · 3 marks
7.2 A hydrochloric acid solution, HCℓ(aq), is standardised by titrating it against $25$ cm $^{3}$ of a $0, 04$ mol·dm $^{- 3}$ sodium carbonate solution $Na_{2} CO_{3}$ (aq). At the endpoint, it is found that $19, 5$ cm $^{3}$ of HCℓ(aq) has reacted.

The balanced equation for the reaction is:

$Na_{2} CO_{3} (aq) + 2 HCl(aq) \to 2 NaCl(aq) + CO_{2} (g) + H_{2} O (ℓ)$

Answer the questions that follow.
7.2.4 Will the pH of the solution at the end of the titration be GREATER THAN 7, EQUAL TO 7 or LESS THAN 7?

Write down the relevant equation as motivation for the answer.(3)
Show the memo (3 ticks)Memo
1. ✓
  pH predictionLess than 7
  1 mark · Predict salt pH and choose indicator
2. ✓
  Reactants $NH_{4}^{+} (aq) + H_{2} O (ℓ)$
  1 mark · Write acid-base reaction equations
3. ✓
  Products $NH_{4}^{+} (aq) + H_{2} O (ℓ) ⇌ NH_{3} (aq) + H_{3} O^{+} (aq)$
  1 mark · Write acid-base reaction equations
6. Question 7.3 · May/June 2025 · Paper 2 · National (DBE) · 6 marks
An unknown acid H $_{x}$ Y is investigated.

During a titration, $23, 64$ cm $^{3}$ of a $0, 11$ mol·dm $^{- 3}$ H $_{x}$ Y solution neutralises $20$ cm $^{3}$ of a $0, 26$ mol·dm $^{- 3}$ NaOH solution.
7.3 Calculate the value of x. Hence, write down the balanced equation for this reaction.(6)
Show the memo (6 ticks)Memo
1. ✓
  (a) Calculate n(HxY) $n = c V$
  $n_{acid} = (0, 11) (0, 02364) = 2, 6 \times 1 0^{- 3}$ mol
  1 mark · Calculate concentration of a solution
2. ✓
  (b) Calculate n(NaOH) $n_{base} = (0, 26) (0, 02) = 5, 2 \times 1 0^{- 3}$ mol ( $0, 0052$ )
  1 mark · Calculate concentration of a solution
3. ✓
  (c) x = 2 $\frac{n ( H _{x} Y )}{n ( NaOH )} = \frac{n _{a}}{n _{b}}$ : $\frac{2 , 6 \times 1 0 ^{- 3}}{5 , 2 \times 1 0 ^{- 3}} = \frac{1}{n _{b}}$
  $n_{b} = 2$ , so $x = 2$
  1 mark · Do titration calculations
4. ✓
  Reactants $H_{2} Y(aq) + NaOH(aq) \to$
  1 mark · Write acid-base reaction equations
5. ✓
  Products $\to Na_{2} Y(aq) + H_{2} O (ℓ)$
  1 mark · Write acid-base reaction equations
6. ✓
  Balancing $H_{2} Y(aq) + 2 NaOH(aq) \to Na_{2} Y(aq) + 2 H_{2} O (ℓ)$
  1 mark · Balance a chemical equation

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