smc-3673-40-Properties of Common A/B

CHEMISTRY, M6 2015 VCE 23 MC

The following table shows the value of the ionisation constant of pure water at various temperatures and at a constant pressure.

\(\text{Temperature (°C)}\)	\(0\)	\(25\)	\(50\)	\(75\)	\(100\)
\(K_W\)	\( 1.1 \times 10^{-15}\)	\( 1.0 \times 10^{-14}\)	\( 5.5 \times 10^{-14}\)	\( 2.0 \times 10^{-13}\)	\( 5.6 \times 10^{-13}\)

Given this data, which one of the following statements about pure water is correct?

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\(B\)

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\(\ce{2H2O(l) \rightleftharpoons H3O+(aq) + OH-(aq)} \)

→ Table shows that \(K_W\) increases as temperature increases.

→ Ionisation equation shifts right as temperature increases, causing an increase in \(\ce{[H3O+]}\) and \(\ce{[OH-]}\) (eliminate A).

→ pH decreases as \(\ce{[H3O+]}\) and temperature increase (eliminate C).

→ pH of water = 7 at 25°C only (eliminate D).

\(\Rightarrow B\)

♦ Mean mark 55%.

The structure of an organic compound is shown.

Which row of the table correctly shows how this compound reacts with bromine water and with blue litmus?

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`D`

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→ Organic compound is sorbic acid.

→ Bromine water changes from a bright yellow to a colourless solution when it reacts with sorbic acid.

→ The acidic nature of the organic compound will turn blue litmus red.

`=>D`

Equimolar solutions of `text{NaCl}(aq), text{NH}_(4) text{Cl}(aq)` and `text{NaCH}_(3) text{COO}(aq)` were prepared.

In which of the following are these salt solutions listed from least to most acidic?

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`D`

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→ \( \ce{NaCl} \) is a neutral salt, \( \ce{NH4Cl} \) is an acidic salt and \( \ce{NaCH3COO} \) is a basic salt.

→ Therefore, least to most acidic: \( \ce{NaCH3COO(aq), NaCl(aq), NH4Cl(aq)} \)

`=> D`

♦ Mean mark 42%.