[Maximum number: 1]

Hydrogen iodide, HI, is a colourless gas at room temperature.

(a)

In the laboratory, HI(aq) can be formed in a two-step process.

step $13 \mathrm{I}_{2}(\mathrm{~s})+2 \mathrm{P}(\mathrm{s}) \rightarrow 2 \mathrm{PI}_{3}(\mathrm{~s})$

step $2 \mathrm{PI}_{3}(\mathrm{~s})+3 \mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \rightarrow \mathrm{H}_{3} \mathrm{PO}_{3}(\mathrm{aq})+3 \mathrm{HI}(\mathrm{aq})$

[ 1 ]

(i)

Give the formula of the conjugate base of $\mathrm{H}_{3} \mathrm{PO}_{3}$ .

[ 1 ]

[Maximum number: 1]

Sulfides are compounds that contain sulfur but not oxygen.

(a)

Hydrogen sulfide gas, $\mathrm{H}_{2} \mathrm{~S}(\mathrm{~g})$ , is slightly soluble in water. It acts as a weak acid in aqueous solution.

[ 1 ]

(i)

Give the formula of the conjugate base of $\mathrm{H}_{2} \mathrm{~S}$ .

[ 1 ]

(a)

Barium hydroxide, $\mathrm{Ba}(\mathrm{OH})_{2}$ , is a strong base.

A $250.0 \mathrm{~cm}^{3}$ solution of $\mathrm{Ba}(\mathrm{OH})_{2}$ with a pH of 12.2 is made by dissolving $\mathrm{Ba}(\mathrm{OH})_{2}$ in distilled water.

Calculate the mass of $\mathrm{Ba}(\mathrm{OH})_{2}$ required to make this solution.
Show your working.
$\left[M_{\mathrm{r}}: \mathrm{Ba}(\mathrm{OH})_{2}, 171.3\right]$

\text { mass of } \mathrm{Ba}(\mathrm{OH})_{2}=

[ 3 ]

(b)

The solubility of iron(II) hydroxide, $\mathrm{Fe}(\mathrm{OH})_{2}$ , is $5.85 \times 10^{-6} \mathrm{moldm}^{-3}$ at 298 K .

[ 4 ]

(i)

Write the expression for the solubility product, $\mathrm{K}_{\mathrm{sp}}$ , of $\mathrm{Fe}(\mathrm{OH})_{2}$ .

K_{s p}=

[ 1 ]

(ii)

Calculate the value of $K_{\mathrm{sp}}$ of $\mathrm{Fe}(\mathrm{OH})_{2}$ . Include its units.

\begin{gathered} K_{s p}= \\ \text { units }= \end{gathered}

[ 3 ]

[Maximum number: 2]

Potassium iodide, KI, is used as a reagent in both inorganic and organic chemistry.

(a)

Table 1.1 gives some data about the halide ions, $\mathrm{Cl}^{-}, \mathrm{Br}^{-}$ and $\mathrm{I}^{-}$ , and their potassium salts.

Table 1.1

[ 2 ]

(i)

Solid $\mathrm{PbI}_{2}$ forms when KI(aq) is mixed with $\mathrm{Pb}^{2+}(\mathrm{aq})$ ions.

The solubility product, $K_{\mathrm{sp}}$ , of $\mathrm{PbI}_{2}$ is $7.1 \times 10^{-9} \mathrm{~mol}^{3} \mathrm{dm}^{-9}$ at $25^{\circ} \mathrm{C}$ .
Calculate the solubility, in $\mathrm{moldm}^{-3}$ , of $\mathrm{PbI}_{2}(\mathrm{~s})$ .

\text { solubility of } \mathrm{PbI}_{2}(\mathrm{~s})=

mol dm ${ }^{-3}$

[ 2 ]

[Maximum number: 1]

Propanone, $\mathrm{CH}_{3} \mathrm{COCH}_{3}$ , reacts with iodine, $\mathrm{I}_{2}$ , in the presence of an acid catalyst.

\mathrm{CH}_{3} \mathrm{COCH}_{3}+\mathrm{I}_{2} \rightarrow \mathrm{CH}_{3} \mathrm{COCH}_{2} \mathrm{I}+\mathrm{H}^{+}+\mathrm{I}^{-}

The rate equation for this reaction is shown.

\text { rate }=k\left[\mathrm{CH}_{3} \mathrm{COCH}_{3}\right]\left[\mathrm{H}^{+}\right]

(a)

A four-step mechanism is suggested for the overall reaction.

\mathrm{CH}_{3} \mathrm{COCH}_{3}+\mathrm{I}_{2} \rightarrow \mathrm{CH}_{3} \mathrm{COCH}_{2} \mathrm{I}+\mathrm{H}^{+}+\mathrm{I}^{-} \quad \text { rate }=k\left[\mathrm{CH}_{3} \mathrm{COCH}_{3}\right]\left[\mathrm{H}^{+}\right]

Part of this mechanism is shown.

step 1: $\mathrm{CH}_{3} \mathrm{COCH}_{3}+\mathrm{H}^{+} \rightarrow \mathrm{CH}_{3} \mathrm{C}^{+}(\mathrm{OH}) \mathrm{CH}_{3}$

step 2: $\quad \mathrm{CH}_{3} \mathrm{C}^{+}(\mathrm{OH}) \mathrm{CH}_{3} \rightarrow \mathrm{CH}_{3} \mathrm{C}(\mathrm{OH})=\mathrm{CH}_{2}+\mathrm{H}^{+}$

step 3: →

step 4: $\quad \mathrm{CH}_{3} \mathrm{C}^{+}(\mathrm{OH}) \mathrm{CH}_{2} \mathrm{I} \rightarrow \mathrm{CH}_{3} \mathrm{COCH}_{2} \mathrm{I}+\mathrm{H}^{+}$

[ 1 ]

(i)

Identify one conjugate acid-conjugate base pair in the mechanism. conjugate acid conjugate base

[ 1 ]

(a)

The solubility product, $K_{\mathrm{sp}}$ , of $\mathrm{BaSO}_{4}$ is $1.08 \times 10^{-10} \mathrm{~mol}^{2} \mathrm{dm}^{-6}$ at 298 K .

Calculate the solubility of $\mathrm{BaSO}_{4}$ in g per $100 \mathrm{~cm}^{3}$ of solution.
solubility of $\mathrm{BaSO}_{4}=$ g per $100 \mathrm{~cm}^{3}$ of solution

[ 2 ]

(a)

The solubility of $\mathrm{Be}(\mathrm{OH})_{2}$ in water is $2.40 \times 10^{-6} \mathrm{gdm}^{-3}$ at 298 K .

[ 4 ]

(i)

Write an expression for the solubility product, $K_{\mathrm{sp}}$ , of $\mathrm{Be}(\mathrm{OH})_{2}$ and state its units.

K_{s p}=

units =

[ 2 ]

(ii)

Calculate the numerical value of $K_{\mathrm{sp}}$ for $\mathrm{Be}(\mathrm{OH})_{2}$ at 298 K .

K_{s p}=

[ 2 ]

[Maximum number: 3]

Iodine is found naturally in compounds in many different oxidation states.

(a)

An orange precipitate of $\mathrm{HgI}_{2}$ forms when $\mathrm{Hg}^{2+}$ ions are added to KI(aq). The solubility of $\mathrm{HgI}_{2}$ at $25^{\circ} \mathrm{C}$ is $1.00 \times 10^{-7} \mathrm{gdm}^{-3}$ .

Calculate the solubility product, $K_{\mathrm{sp}}$ , of $\mathrm{HgI}_{2}$ . Include units in your answer.
$\left[M_{\mathrm{r}}: \mathrm{HgI}_{2}, 454.4\right]$
value of $K_{s p}=$
units =

[ 3 ]

(a)

Calcium hydroxide is slightly soluble in water.

[ 4 ]

(i)

Write an equation to show the dissociation of calcium hydroxide, $\mathrm{Ca}(\mathrm{OH})_{2}(\mathrm{~s})$ , in aqueous solution. Include state symbols. ⇌

[ 1 ]

(ii)

Calculate the solubility, in $\mathrm{mol} \mathrm{dm}^{-3}$ , of $\mathrm{Ca}(\mathrm{OH})_{2}$ .
$\left[K_{\mathrm{sp}}: \mathrm{Ca}(\mathrm{OH})_{2}, 5.02 \times 10^{-6} \mathrm{~mol}^{3} \mathrm{dm}^{-9}\right]$
solubility = $\mathrm{mol} \mathrm{dm}^{-3}$

[ 2 ]

(iii)

Suggest how the solubility of $\mathrm{Ca}(\mathrm{OH})_{2}$ in aqueous NaOH compares to its solubility in water.

Explain your reasoning.

[ 1 ]

(a)

Calcium hydroxide is slightly soluble in water.

[ 4 ]

(i)

Write an equation to show the dissociation of calcium hydroxide, $\mathrm{Ca}(\mathrm{OH})_{2}(\mathrm{~s})$ , in aqueous solution. Include state symbols. ⇌

[ 1 ]

(ii)

Calculate the solubility, in $\mathrm{mol} \mathrm{dm}^{-3}$ , of $\mathrm{Ca}(\mathrm{OH})_{2}$ .
$\left[K_{\mathrm{sp}}: \mathrm{Ca}(\mathrm{OH})_{2}, 5.02 \times 10^{-6} \mathrm{~mol}^{3} \mathrm{dm}^{-9}\right]$
solubility = $\mathrm{mol} \mathrm{dm}^{-3}$

[ 2 ]

(iii)

Suggest how the solubility of $\mathrm{Ca}(\mathrm{OH})_{2}$ in aqueous NaOH compares to its solubility in water.

Explain your reasoning.

[ 1 ]