[Maximum number: 2]

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

(a)

Iodide ions, $\mathrm{I}^{-}$ , react with acidified $\mathrm{H}_{2} \mathrm{O}_{2}(\mathrm{aq})$ to form iodine, $\mathrm{I}_{2}$ , and water. This reaction mixture is shaken with cyclohexane, $\mathrm{C}_{6} \mathrm{H}_{12}$ , to extract the $\mathrm{I}_{2}$ . Cyclohexane is immiscible with water.

[ 2 ]

(i)

$15.0 \mathrm{~cm}^{3}$ of $\mathrm{C}_{6} \mathrm{H}_{12}$ is shaken with $20.0 \mathrm{~cm}^{3}$ of an aqueous solution containing $\mathrm{I}_{2}$ until no further change is seen.
It is found that 0.390 g of $\mathrm{I}_{2}$ is extracted into the $\mathrm{C}_{6} \mathrm{H}_{12}$ .
The partition coefficient of $\mathrm{I}_{2}$ between $\mathrm{C}_{6} \mathrm{H}_{12}$ and water, $K_{\mathrm{pc}}$ , is 93.8.
Calculate the mass of $\mathrm{I}_{2}$ that remains in the aqueous layer.
Show your working.
mass of $I_{2}$ in aqueous layer =

(ii)

Suggest how the value of $K_{p c}$ of $\mathrm{I}_{2}$ between hexan-2-one, $\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{3} \mathrm{COCH}_{3}$ , and water compares to the value given in (a)(ii). Explain your answer.

[ 2 ]

(a)

(i)

Explain what is meant by the term partition coefficient, $K_{\text {partition }}$ .

[ 2 ]

(ii)

The partition coefficient of organic compound H between dichloromethane and water is 4.75.
- 2.50 g of compound H was dissolved in water and made up to $100 \mathrm{~cm}^{3}$ in a volumetric flask.
- $50 \mathrm{~cm}^{3}$ of this aqueous solution were shaken with $10 \mathrm{~cm}^{3}$ of dichloromethane.

Calculate the mass of compound H that was extracted into the dichloromethane.
mass of compound H extracted =

[ 2 ]

[Maximum number: 6]

Ethoxyethane, $\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OC}_{2} \mathrm{H}_{5}$ , can dissolve both in water and in octan-1-ol. The expression and numerical value for the partition coefficient of ethoxyethane between water and octan-1-ol are given. Water and octan-1-ol are immiscible.

K_{\mathrm{pc}}=\frac{\text { concentration of } \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OC}_{2} \mathrm{H}_{5} \text { in octan-1-ol }}{\text { concentration of } \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OC}_{2} \mathrm{H}_{5} \text { in water }}=6.760 \text { at } 20^{\circ} \mathrm{C}

(a)

In an experiment, octan-1-ol at $20^{\circ} \mathrm{C}$ is added to a solution of ethoxyethane in water at $20^{\circ} \mathrm{C}$ . The mixture is analysed immediately and a value of $K_{p c}$ is calculated.

The calculation is performed correctly; the value calculated is 5.625 .
Explain why the value calculated is less than 6.760.

[ 2 ]

(b)

A second experiment is performed and the value of $K_{\mathrm{pc}}$ is found to be 6.760. The concentration of ethoxyethane in the octan-1-ol layer is $7.62 \mathrm{~g} \mathrm{dm}^{-3}$ .

[ 4 ]

(i)

Calculate the concentration, in $\mathrm{g} \mathrm{dm}^{-3}$ , of ethoxyethane in the aqueous layer. $\mathrm{gdm}^{-3}$

[ 1 ]

(ii)

$100 \mathrm{~cm}^{3}$ of the octan-1-ol layer is taken and shaken with $100 \mathrm{~cm}^{3}$ of water.

Calculate the maximum amount, in mol, of ethoxyethane that can be extracted into the water.
mol

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(a)

The partition coefficient, $K_{\mathrm{pc}}$ , of a substance, Q, between hexane and water is 7.84 at 298 K . Q is more soluble in hexane than it is in water.

[ 3 ]

(i)

Define partition coefficient, $K_{\mathrm{pc}}$ .

[ 1 ]

(ii)

5.00 g of Q is shaken with a mixture of $100.0 \mathrm{~cm}^{3}$ of water and $100.0 \mathrm{~cm}^{3}$ of hexane at 298 K and left until there is no further change in concentrations.
Calculate the mass of Q dissolved in the water.
mass of Q =

(iii)

A sample of Q is shaken with a different mixture of water and hexane and left until there is no further change in concentrations.

It is found that the mass of Q dissolved in each solvent is the same.
Use the $K_{p c}$ value to suggest possible values for the volume of water used and the volume of hexane used.
volume of water = $\mathrm{cm}^{3}$
volume of hexane = $\mathrm{cm}^{3}$

[ 1 ]

(iv)

Q is more soluble in hexane than it is in water.

It is suggested that Q is one of $\mathrm{KCl}, \mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{4} \mathrm{OH}$ or HCOOH .
Identify Q. Explain your answer.

[ 1 ]

(a)

Water and octan-1-ol form two layers when mixed.

Ethanamide is more soluble in water than it is in octan-1-ol. When 1.00 g of ethanamide is added to $50.0 \mathrm{~cm}^{3}$ of water and this is then shaken with $50.0 \mathrm{~cm}^{3}$ of octan-1-ol, it is found that the water layer contains 0.935 g of ethanamide at equilibrium.

[ 3 ]

(i)

Calculate the partition coefficient, $K_{\mathrm{pc}}$ , for ethanamide in water and octan-1-ol.

K_{p c}=

[ 1 ]

(ii)

The $50.0 \mathrm{~cm}^{3}$ of water containing 0.935 g of ethanamide is then shaken with $100.0 \mathrm{~cm}^{3}$ of pure octan-1-ol under the same conditions.

Calculate the mass of ethanamide that is dissolved in the $100.0 \mathrm{~cm}^{3}$ of octan-1-ol at equilibrium.
mass of ethanamide = g

[ 2 ]

(a)

A sample of butanoic acid, $\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{2} \mathrm{COOH}$ , is shaken with a mixture of two immiscible solvents, ethoxyethane and water. The solvents form two layers. The butanoic acid is distributed between the two layers, its concentration in ethoxyethane being higher than its concentration in water.

[ 3 ]

(i)

State what is meant by partition coefficient.

[ 1 ]

(ii)

The partition coefficient, $K_{\mathrm{pc}}$ , for butanoic acid between ethoxyethane and water is 3.50 .

A solution of 2.00 g of butanoic acid in $100 \mathrm{~cm}^{3}$ ethoxyethane is added to water. This mixture is left until there is no further change in the concentration of butanoic acid in either solvent. The mass of butanoic acid dissolved in the ethoxyethane layer is now 1.62 g .

Calculate the volume of water used.
volume of water used = $\mathrm{cm}^{3}$

[ 2 ]

(a)

(i)

State what is meant by the term partition coefficient.

Ammonia is soluble in both water and organic solvents.
An aqueous solution of ammonia is shaken with the immiscible organic solvent trichloromethane. The mixture is left to reach equilibrium.

Samples are taken from each layer and titrated with dilute hydrochloric acid.
- A $25.0 \mathrm{~cm}^{3}$ sample from the trichloromethane layer requires $13.0 \mathrm{~cm}^{3}$ of $0.100 \mathrm{moldm}^{-3}$ HCl to reach the end-point.
- A $10.0 \mathrm{~cm}^{3}$ sample from the aqueous layer requires $12.5 \mathrm{~cm}^{3}$ of $0.100 \mathrm{~mol} \mathrm{dm}^{-3} \mathrm{HCl}$ to reach the end-point.

[ 1 ]

(ii)

Calculate the partition coefficient, $K_{\text {partition }}$ , of ammonia between trichloromethane and water.

K_{\text {partition }}=

[ 2 ]

(iii)

Butylamine, $\mathrm{C}_{4} \mathrm{H}_{9} \mathrm{NH}_{2}$ , is also soluble in both water and organic solvents.

Suggest how the value of $K_{\text {partition }}$ of butylamine between trichloromethane and water would compare to the value of $K_{\text {partition }}$ calculated in (ii). Explain your answer.

[ 2 ]

[Maximum number: 2]

Nitrobenzene, $\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NO}_{2}$ , can be reduced to phenylamine, $\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}$ , in acid solution in a two step process.

(a)

Following the reaction in (b), an excess of NaOH(aq) was added to liberate phenylamine from phenylammonium chloride.

[ 2 ]

(i)

Use the data to calculate the partition coefficient, $K_{\text {partition }}$ , of phenylamine between dichloromethane and water.

[ 2 ]

(a)

Define the term partition coefficient, $K_{\mathrm{pc}}$ .

[ 2 ]

(b)

$K_{\mathrm{pc}}$ of benzoic acid between octan-1-ol and water is 79.4.

[ 1 ]

(i)

A solution of 0.400 g of benzoic acid in $25.0 \mathrm{~cm}^{3}$ octan-1-ol is shaken with $125 \mathrm{~cm}^{3}$ of water. Calculate the mass of benzoic acid extracted into the water layer.
mass of benzoic acid extracted =

(ii)

$\mathrm{K}_{\mathrm{pc}}$ of benzophenone, $\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COC}_{6} \mathrm{H}_{5}$ , between octan-1-ol and water is different from the value of $K_{\mathrm{pc}}$ of benzoic acid given in (b)(i).

Explain why.

[ 1 ]

(a)

(i)

State what is meant by partition coefficient, $K_{\mathrm{pc}}$ .

[ 1 ]

(ii)

The partition coefficient, $K_{p c}$ , for a compound, X, between carbon disulfide, $\mathrm{CS}_{2}$ , and water is 10.5 .
1.85 g of X is dissolved in water and made up to $100.0 \mathrm{~cm}^{3}$ in a volumetric flask. $40.0 \mathrm{~cm}^{3}$ of this aqueous solution is shaken with $25.0 \mathrm{~cm}^{3}$ of $\mathrm{CS}_{2}$ .
The mixture is left to reach equilibrium.
Calculate the mass of X, in g , extracted into the $\mathrm{CS}_{2}$ layer.

mass of X =

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