Question

QUESTION 7 [23 marks]
Consider the reaction below:
HSO4
- + HCO3
- → SO4
2- + H2CO3
Question 7.1 [2 marks]
Define a Lowry-Brønsted base.
Question 7.2 [6 marks]
Rewrite the chemical equation and indicate with the help of lines and arrows the
conjugated acid-base pairs. Clearly indicate the conjugated acid and base pairs
for the forward and reverse reactions. You may use colour to help distinguish
the labels.
Question 7.3 [2 marks]
Identify the substance(s) that are considered ampholytes from the above
reaction.
Question 7.4 [3 marks]
Write down the balanced chemical equation for the reaction when Magnesium
Oxide (MgO) reacts with Nitric Acid.
Question 7.5
50 g of IMPURE calcium carbonate reacts with 200 cm3 of a dilute
sulphuric acid with a concentration of 1,5 mol∙dm-3 All the calcium carbonate
and sulphuric acid react completely leaving the impurities unreacted at the

Answer 1

**Question 7.1 [2 marks]**

A Lowry-Brønsted base is defined as a species that can accept a proton (H⁺ ion) from another species during a chemical reaction. In essence, it acts as a proton acceptor.

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**Question 7.2 [6 marks]**

The reaction can be rewritten as follows, with the conjugate acid-base pairs indicated:

\[ \text{HSO}_4^- + \text{HCO}_3^- \rightarrow \text{SO}_4^{2-} + \text{H}_2\text{CO}_3 \]

**Conjugate Acid-Base Pairs**:
1. For the forward reaction:
- **HSO₄⁻ (acid)** ⇔ **SO₄²⁻ (conjugate base)**
- **HCO₃⁻ (base)** ⇔ **H₂CO₃ (conjugate acid)**

2. For the reverse reaction:
- **SO₄²⁻ (base)** ⇔ **HSO₄⁻ (conjugate acid)**
- **H₂CO₃ (acid)** ⇔ **HCO₃⁻ (conjugate base)**

You may highlight or use color coding to make the pairs stand out, for instance:
- Red for acids (HSO₄⁻, H₂CO₃)
- Blue for bases (SO₄²⁻, HCO₃⁻)

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**Question 7.3 [2 marks]**

The ampholytes in the reaction are:
1. HSO₄⁻ (hydrogen sulfate ion) - It can act as either an acid or a base depending on the reaction conditions.
2. HCO₃⁻ (bicarbonate ion) - It can also act as either an acid or a base depending on the reaction conditions.

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**Question 7.4 [3 marks]**

The balanced chemical equation for the reaction when magnesium oxide (MgO) reacts with nitric acid (HNO₃) is:

\[ \text{MgO} + 2 \text{HNO}_3 \rightarrow \text{Mg(NO}_3\text{)}_2 + \text{H}_2\text{O} \]

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**Question 7.5 [incomplete]**

Given that you mentioned 50 g of IMPURE calcium carbonate reacts with 200 cm³ of a dilute sulfuric acid with a concentration of 1.5 mol∙dm⁻³, you may need to proceed with these steps to solve the problem:

1. **Determine moles of sulfuric acid:**
\[ \text{Volume of H₂SO₄} = 200 \, \text{cm}^3 = 0.200 \, \text{dm}^3 \]
\[ \text{Moles of H₂SO₄} = \text{Concentration} \times \text{Volume} = 1.5 \, \text{mol/dm}^3 \times 0.200 \, \text{dm}^3 = 0.3 \, \text{mol} \]

2. **Balanced reaction with calcium carbonate (CaCO₃):**
The balanced reaction for calcium carbonate with sulfuric acid is:
\[ \text{CaCO}_3 + \text{H}_2\text{SO}_4 \rightarrow \text{CaSO}_4 + \text{H}_2\text{O} + \text{CO}_2 \]

From this equation, you can see that 1 mole of CaCO₃ reacts with 1 mole of H₂SO₄.

3. **Determine how many moles of CaCO₃ could react with sulfuric acid using the 0.3 moles of H₂SO₄**:
Therefore, 0.3 moles of H₂SO₄ will react with 0.3 moles of CaCO₃.

4. **Use the molar mass to find the mass of CaCO₃**:
The molar mass of CaCO₃ is approximately 100.09 g/mol.
\[ \text{Mass of CaCO}_3 = \text{moles} \times \text{molar mass} = 0.3 \, \text{mol} \times 100.09 \, \text{g/mol} \approx 30.03 \, \text{g} \]

So if 30.03 g of calcium carbonate reacts, you can find the purity or impurities accordingly in the 50 g sample. However, since the question was incomplete, further details from that section would be helpful for the final steps.