Solved: Copper forms two chlorides, copper(I) chloride and copper(II) chloride. Two... [IB Chemistry]

Copper forms two chlorides, copper(I) chloride and copper(II) chloride.

Question

HLPaper 2

Copper forms two chlorides, copper(I) chloride and copper(II) chloride.

Two electrolysis cells were assembled using graphite electrodes and connected in series as shown.

Copper(I) chloride undergoes a disproportionation reaction, producing copper(II) chloride and copper.

2Cu+ (aq) → Cu (s) + Cu2+ (aq)

Dilute copper(II) chloride solution is light blue, while copper(I) chloride solution is colourless.

Copper(II) chloride is used as a catalyst in the production of chlorine from hydrogen chloride.

4HCl (g) + O2 (g) → 2Cl2 (g) + 2H2O (g)

Calculate the standard enthalpy change, Δ_H_θ, in kJ, for this reaction, using section 12 of the data booklet.

[2]

Verified

Solution

$\Delta H^\circ = \sum\Delta H^\circ_f(\text{products}) - \sum\Delta H^\circ_f(\text{reactants})$ 1 mark
$\Delta H^\circ = 2(-241.8) - 4(-92.3) = -114.4$ kJ 1 mark

State the electron configuration of the Cu+ ion.

[1]

Verified

Solution

$[Ar]3d^{10}$ OR $1s^2 2s^2 2p^6 3s^2 3p^6 3d^{10}$ 1 mark

Explain how the catalyst increases the rate of the reaction.

[2]

Verified

Solution

Catalyst provides an alternative reaction pathway 1 mark
Lower activation energy ( $E_a$ ) OR Higher proportion of particles with kinetic energy greater than or equal to catalyzed activation energy ( $E \geq E_{a(cat)}$ ) 1 mark

State how current is conducted through the wires and through the electrolyte.

[2]

Verified

Solution

In wires: delocalized electrons flow 1 mark
In electrolyte: mobile ions flow 1 mark

Write the half-equation for the formation of gas bubbles at electrode 1.

[1]

Verified

Solution

${2Cl^-} \rightarrow Cl_2(g) + 2e^-$ 1 mark

${Cl^-} \rightarrow \frac{1}{2}Cl_2(g) + e^-$ 1 mark

Accept e for e−

Bubbles of gas were also observed at another electrode. Identify the electrode and the gas.

[1]

Verified

Solution

Anode AND oxygen/O ${_2}$ 1 mark

Chlorine/Cl ${_2}$ is also acceptable

Deduce the half-equation for the formation of the gas identified in

[1]

Verified

Solution

$\ce{2H2O (l) -> 4H+ (aq) + O2 (g) + 4e-}$ 1

Alternative equations accepted:

$\ce{2Cl- (aq) -> Cl2 (g) + 2e-}$
$\ce{4OH- -> 2H2O + O2 + 4e-}$

Calculate the cell potential at 298 K for the disproportionation reaction, in V, using section 24 of the data booklet.

[1]

Verified

Solution

${E^{\ominus}} = +0.52 - 0.15 = +0.37$ «V» 1 mark

Comment on the spontaneity of the disproportionation reaction at 298 K.

[1]

Verified

Solution

Reaction is spontaneous AND ${E^{\ominus}}$ is positive 1 mark

10.

Calculate the standard Gibbs free energy change, Δ_G_θ, to two significant figures, for the disproportionation at 298 K. Use your answer from (e)(i) and sections 1 and 2 of the data booklet.

[1]

Verified

Solution

$\Delta G^\theta = -nFE^\theta = -1 \text{ mol} \times 96500 \text{ C mol}^{-1} \times 0.37 \text{ V} = -36000 \text{ J} = -36 \text{ kJ}$ 1

Accept "-18 kJ mol⁻¹ per mole of Cu⁺"

Do not accept values of n other than 1

Answer must be given to 2 significant figures

Accept J/kJ or J mol⁻¹/kJ mol⁻¹ for units

11.

Suggest, giving a reason, whether the entropy of the system increases or decreases during the disproportionation.

e(iv).

[1]

Verified

Solution

2 mol (aq) → 1 mol (aq) AND decreases ✔

NOTE:Accept “solid formed from aqueous solution AND decreases”.
Do not accept 2 mol → 1 mol without (aq).

e(iv).

12.

Deduce, giving a reason, the sign of the standard enthalpy change, Δ_H_θ, for the disproportionation reaction at 298 K.

[1]

Verified

Solution

Either: $\Delta G^\circ < 0$ AND $\Delta S^\circ < 0$ AND $\Delta H^\circ < 0$ 1 mark
Or: $\Delta G^\circ + T\Delta S^\circ < 0$ AND $\Delta H^\circ < 0$ 1 mark

13.

Predict, giving a reason, the effect of increasing temperature on the stability of copper(I) chloride solution.

[1]

Verified

Solution

$T\Delta S$ becomes more negative (reducing spontaneity) AND stability increases 1

Accept calculation showing non-spontaneity at 433 K

14.

Describe how the blue colour is produced in the Cu(II) solution. Refer to section 17 of the data booklet.

[3]

Verified

Solution

Ligands cause splitting of d-orbitals 1
Light absorbed when electrons transition to higher energy level in d-d transitions 1
Energy gap corresponds to orange light in visible spectrum 1
Blue color observed is complementary to absorbed orange light 1

Maximum 3 marks total

15.

Deduce why the Cu(I) solution is colourless.

[1]

Verified

Solution

Full 3d subshell/orbitals OR no d-d transitions possible (and therefore no colour) 1

16.

When excess ammonia is added to copper(II) chloride solution, the dark blue complex ion, $Cu(NH3)4(H2O)2$ 2+, forms.

State the molecular geometry of this complex ion, and the bond angles within it.

[1]

Verified

Solution

Molecular geometry: octahedral (or square-based bipyramid) AND bond angles: 90° (180° for axial bonds) 1

Accept square-based bipyramid as alternative terminology

17.

Examine the relationship between the Brønsted–Lowry and Lewis definitions of a base, referring to the ligands in the complex ion $[CuCl_4]^{2-}$ .

[2]

Verified

Solution

Any two of:
ligand/chloride ion Lewis base AND donates e-pair ✔
not Brønsted–Lowry base AND does not accept proton/H+ ✔
Lewis definition extends/broader than Brønsted–Lowry definition ✔

18.

Determine the enthalpy of solution of copper(II) chloride, using data from sections 18 and 20 of the data booklet.

The enthalpy of hydration of the copper(II) ion is $-2161 \text{ kJ mol}^{-1}$ .

[2]

Verified

Solution

Enthalpy of solution = lattice enthalpy + enthalpies of hydration (of Cu $^{2+}$ and Cl $^-$ ) 1 mark
$\Delta H_{sol} = +2824 - 2161 - 2(359) = -55 \text{ kJ mol}^{-1}$ 1 mark

Accept enthalpy cycle Award full marks for correct final answer

19.

Solid copper(II) chloride absorbs moisture from the atmosphere to form a hydrate of formula CuCl2•xH2O.

A student heated a sample of hydrated copper(II) chloride, in order to determine the value of x. The following results were obtained:

Mass of crucible = 16.221 g
Initial mass of crucible and hydrated copper(II) chloride = 18.360 g
Final mass of crucible and anhydrous copper(II) chloride = 17.917 g

Determine the value of x.

[3]

Verified

Solution

Mass of $\text{H}_2\text{O} = 18.360 \text{ g} - 17.917 \text{ g} = 0.443 \text{ g}$ AND mass of $\text{CuCl}_2 = 17.917 \text{ g} - 16.221 \text{ g} = 1.696 \text{ g}$ 1
Moles of $\text{H}_2\text{O} = \frac{0.443 \text{ g}}{18.02 \text{ g mol}^{-1}} = 0.0246 \text{ mol}$ OR Moles of $\text{CuCl}_2 = \frac{1.696 \text{ g}}{134.45 \text{ g mol}^{-1}} = 0.0126 \text{ mol}$ 1
Ratio water : copper(II) chloride = 1.95 : 1 Therefore $x = 2$ 1

Accept x = 1.95

Award [3] for correct final answer

Copper forms two chlorides, copper(I) chloride and copper(II) chloride.

Question

HLPaper 2

Copper forms two chlorides, copper(I) chloride and copper(II) chloride.

Two electrolysis cells were assembled using graphite electrodes and connected in series as shown.

Copper(I) chloride undergoes a disproportionation reaction, producing copper(II) chloride and copper.

2Cu+ (aq) → Cu (s) + Cu2+ (aq)

Dilute copper(II) chloride solution is light blue, while copper(I) chloride solution is colourless.

Copper(II) chloride is used as a catalyst in the production of chlorine from hydrogen chloride.

4HCl (g) + O2 (g) → 2Cl2 (g) + 2H2O (g)

Calculate the standard enthalpy change, Δ_H_θ, in kJ, for this reaction, using section 12 of the data booklet.

[2]

Verified

Solution

$\Delta H^\circ = \sum\Delta H^\circ_f(\text{products}) - \sum\Delta H^\circ_f(\text{reactants})$ 1 mark
$\Delta H^\circ = 2(-241.8) - 4(-92.3) = -114.4$ kJ 1 mark

State the electron configuration of the Cu+ ion.

[1]

Verified

Solution

$[Ar]3d^{10}$ OR $1s^2 2s^2 2p^6 3s^2 3p^6 3d^{10}$ 1 mark

Explain how the catalyst increases the rate of the reaction.

[2]

Verified

Solution

Catalyst provides an alternative reaction pathway 1 mark
Lower activation energy ( $E_a$ ) OR Higher proportion of particles with kinetic energy greater than or equal to catalyzed activation energy ( $E \geq E_{a(cat)}$ ) 1 mark

State how current is conducted through the wires and through the electrolyte.

[2]

Verified

Solution

In wires: delocalized electrons flow 1 mark
In electrolyte: mobile ions flow 1 mark

Write the half-equation for the formation of gas bubbles at electrode 1.

[1]

Verified

Solution

${2Cl^-} \rightarrow Cl_2(g) + 2e^-$ 1 mark

${Cl^-} \rightarrow \frac{1}{2}Cl_2(g) + e^-$ 1 mark

Accept e for e−

Bubbles of gas were also observed at another electrode. Identify the electrode and the gas.

[1]

Verified

Solution

Anode AND oxygen/O ${_2}$ 1 mark

Chlorine/Cl ${_2}$ is also acceptable

Deduce the half-equation for the formation of the gas identified in

[1]

Verified

Solution

$\ce{2H2O (l) -> 4H+ (aq) + O2 (g) + 4e-}$ 1

Alternative equations accepted:

$\ce{2Cl- (aq) -> Cl2 (g) + 2e-}$
$\ce{4OH- -> 2H2O + O2 + 4e-}$

Calculate the cell potential at 298 K for the disproportionation reaction, in V, using section 24 of the data booklet.

[1]

Verified

Solution

${E^{\ominus}} = +0.52 - 0.15 = +0.37$ «V» 1 mark

Comment on the spontaneity of the disproportionation reaction at 298 K.

[1]

Verified

Solution

Reaction is spontaneous AND ${E^{\ominus}}$ is positive 1 mark

10.

Calculate the standard Gibbs free energy change, Δ_G_θ, to two significant figures, for the disproportionation at 298 K. Use your answer from (e)(i) and sections 1 and 2 of the data booklet.

[1]

Verified

Solution

$\Delta G^\theta = -nFE^\theta = -1 \text{ mol} \times 96500 \text{ C mol}^{-1} \times 0.37 \text{ V} = -36000 \text{ J} = -36 \text{ kJ}$ 1

Accept "-18 kJ mol⁻¹ per mole of Cu⁺"

Do not accept values of n other than 1

Answer must be given to 2 significant figures

Accept J/kJ or J mol⁻¹/kJ mol⁻¹ for units

11.

Suggest, giving a reason, whether the entropy of the system increases or decreases during the disproportionation.

e(iv).

[1]

Verified

Solution

2 mol (aq) → 1 mol (aq) AND decreases ✔

NOTE:Accept “solid formed from aqueous solution AND decreases”.
Do not accept 2 mol → 1 mol without (aq).

e(iv).

12.

Deduce, giving a reason, the sign of the standard enthalpy change, Δ_H_θ, for the disproportionation reaction at 298 K.

[1]

Verified

Solution

Either: $\Delta G^\circ < 0$ AND $\Delta S^\circ < 0$ AND $\Delta H^\circ < 0$ 1 mark
Or: $\Delta G^\circ + T\Delta S^\circ < 0$ AND $\Delta H^\circ < 0$ 1 mark

13.

Predict, giving a reason, the effect of increasing temperature on the stability of copper(I) chloride solution.

[1]

Verified

Solution

$T\Delta S$ becomes more negative (reducing spontaneity) AND stability increases 1

Accept calculation showing non-spontaneity at 433 K

14.

Describe how the blue colour is produced in the Cu(II) solution. Refer to section 17 of the data booklet.

[3]

Verified

Solution

Ligands cause splitting of d-orbitals 1
Light absorbed when electrons transition to higher energy level in d-d transitions 1
Energy gap corresponds to orange light in visible spectrum 1
Blue color observed is complementary to absorbed orange light 1

Maximum 3 marks total

15.

Deduce why the Cu(I) solution is colourless.

[1]

Verified

Solution

Full 3d subshell/orbitals OR no d-d transitions possible (and therefore no colour) 1

16.

When excess ammonia is added to copper(II) chloride solution, the dark blue complex ion, $Cu(NH3)4(H2O)2$ 2+, forms.

State the molecular geometry of this complex ion, and the bond angles within it.

[1]

Verified

Solution

Molecular geometry: octahedral (or square-based bipyramid) AND bond angles: 90° (180° for axial bonds) 1

Accept square-based bipyramid as alternative terminology

17.

Examine the relationship between the Brønsted–Lowry and Lewis definitions of a base, referring to the ligands in the complex ion $[CuCl_4]^{2-}$ .

[2]

Verified

Solution

18.

Determine the enthalpy of solution of copper(II) chloride, using data from sections 18 and 20 of the data booklet.

The enthalpy of hydration of the copper(II) ion is $-2161 \text{ kJ mol}^{-1}$ .

[2]

Verified

Solution

Enthalpy of solution = lattice enthalpy + enthalpies of hydration (of Cu $^{2+}$ and Cl $^-$ ) 1 mark
$\Delta H_{sol} = +2824 - 2161 - 2(359) = -55 \text{ kJ mol}^{-1}$ 1 mark

Accept enthalpy cycle Award full marks for correct final answer

19.

Solid copper(II) chloride absorbs moisture from the atmosphere to form a hydrate of formula CuCl2•xH2O.

A student heated a sample of hydrated copper(II) chloride, in order to determine the value of x. The following results were obtained:

Mass of crucible = 16.221 g
Initial mass of crucible and hydrated copper(II) chloride = 18.360 g
Final mass of crucible and anhydrous copper(II) chloride = 17.917 g

Determine the value of x.

[3]

Verified

Solution

Mass of $\text{H}_2\text{O} = 18.360 \text{ g} - 17.917 \text{ g} = 0.443 \text{ g}$ AND mass of $\text{CuCl}_2 = 17.917 \text{ g} - 16.221 \text{ g} = 1.696 \text{ g}$ 1
Moles of $\text{H}_2\text{O} = \frac{0.443 \text{ g}}{18.02 \text{ g mol}^{-1}} = 0.0246 \text{ mol}$ OR Moles of $\text{CuCl}_2 = \frac{1.696 \text{ g}}{134.45 \text{ g mol}^{-1}} = 0.0126 \text{ mol}$ 1
Ratio water : copper(II) chloride = 1.95 : 1 Therefore $x = 2$ 1

Accept x = 1.95

Award [3] for correct final answer

Copper forms two chlorides, copper(I) chloride and copper(II) chloride.

Related topics

Copper forms two chlorides, copper(I) chloride and copper(II) chloride.

Related topics