QUESTION 7 (Start on a new page.) Hydrated potassium carbonate, K₂CO₃·xH₂O, is a WEAK BASE. A solution is prepared by dissolving some of this solid in water.

Volume used = Final burette reading - Initial burette reading.

7.3.2 q

Volume used = Final burette reading - Initial burette reading.

7.4 METHYL ORANGE is used as the indicator. Explain why methyl orange is the most suitable indicator for this titration by referring to the pH at the equivalence point.
The titration involves a strong acid (HCl) and a weak base ($\text{K}_2\text{CO}_3$). At the equivalence point of such a titration, the resulting solution will be acidic (pH < 7). Methyl orange changes color in the pH range of 3.1 to 4.4, which is suitable for detecting the equivalence point in an acidic medium.

7.5 Calculate the concentration of the $\text{K}_2\text{CO}_3$ solution.
Given:
Concentration of HCl ($C_A$) = $0.1 \text{ mol}\cdot\text{dm}^{-3}$
Volume of HCl ($V_A$) = $25 \text{ cm}^3 = 0.025 \text{ dm}^3$
Balanced equation: $\text{K}_2\text{CO}_3(\text{aq}) + 2\text{HCl}(\text{aq}) \rightarrow 2\text{KCl}(\text{aq}) + \text{CO}_2(\text{g}) + \text{H}_2\text{O}(\text{l})$
Mole ratio $\text{K}_2\text{CO}_3 : \text{HCl}$ is $n_B : n_A = 1:2$.

Convert to $\text{dm}^3$: $V_B = 20.10 \text{ cm}^3 \times \frac{1 \text{ dm}^3}{1000 \text{ cm}^3} = 0.02010 \text{ dm}^3$.

The concentration of the $\text{K}_2\text{CO}_3$ solution is $\boxed{\text{0.0622 mol}\cdot\text{dm}^{-3}}$.

7.6 Calculate the value of x in the formula $\text{K}_2\text{CO}_3 \cdot x\text{H}_2\text{O}$.
The solution from 7.5 was prepared by dissolving $6.525 \text{ g}$ of $\text{K}_2\text{CO}_3 \cdot x\text{H}_2\text{O}$ in $600 \text{ cm}^3$ ($0.600 \text{ dm}^3$) water.
Concentration of $\text{K}_2\text{CO}_3$ ($C_B$) = $0.062189 \text{ mol}\cdot\text{dm}^{-3}$ (from 7.5).

Rounding to the nearest whole number, the value of x is $\boxed{2}$.