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Using standard electrode potentials.
Given $E^\ominus(\ce{Cu^{2+}/Cu})=+0.34\ \text{V}$ and $E^\ominus(\ce{Zn^{2+}/Zn})=-0.76\ \text{V}$.
Part a: Identify the cathode half-cell in the spontaneous cell. (1 mark) Use the correct element-symbol case and ionic charge. A substance name is accepted where appropriate. Part b: Calculate $E^\ominus_{\text{cell}}$. (1 mark) Include the unit V. Part c: State the oxidising agent. (1 mark) Use the correct element-symbol case and ionic charge. A substance name is accepted where appropriate. Writing a full redox equation from half-equations.
Half-equations in reduction form:
$\ce{MnO4^- + 8H+ + 5e^- -> Mn^{2+} + 4H2O}$
$\ce{Fe^{3+} + e^- -> Fe^{2+}}$
Part a: Write the overall ionic equation for reaction of permanganate with iron(II) in acidic solution. (2 marks) Part b: State one common exam error with $E^\ominus$ values when balancing electrons. (1 mark) Faraday calculation: copper deposition.
A current of 2.00 A is passed for 965 s through aqueous $\ce{CuSO4}$ (inert electrodes). Use $F=9.65\times10^4\ \text{C mol}^{-1}$ and $A_r(\ce{Cu})=63.5$. Assume sufficient copper(II) ions and 100% current efficiency for copper deposition.
Part a: Calculate the total charge passed. (1 mark) Include the unit C. Part b: Calculate the mass of copper deposited. (1 mark) Enter the final answer here and show your method in the following field. Include the unit g. Working for part b (2 marks) Gibbs free energy and feasibility.
For a reaction, $E^\ominus_{\text{cell}}=1.10\ \text{V}$ and $n=2$. Use $F=9.65\times10^4\ \text{C mol}^{-1}$.
Part a: Calculate $\Delta G^\ominus$ in kJ mol$^{-1}$. (1 mark) Enter the final answer here and show your method in the following field. Include the unit kJ/mol. Working for part a (1 mark) Part b: State whether the reaction is feasible under standard conditions. (1 mark) Electrolysis products in brine.
Concentrated aqueous $\ce{NaCl}$ is electrolysed using inert electrodes.
Part a: Name the main gas formed at the anode. (1 mark) Use the correct element-symbol case and ionic charge. A substance name is accepted where appropriate. Part b: Write the anode half-equation. (1 mark) Batteries and fuel cells: comparison points.
Compare a rechargeable battery with a hydrogen fuel cell in transport use.
Part a: State one key difference in how energy is supplied during operation. (1 mark) Part b: Write the overall equation for a hydrogen-oxygen fuel cell. (1 mark) Building a cell from a metal half-cell and an ion/ion half-cell.
A zinc rod dips into $1.00\ \text{mol dm}^{-3}$ $\ce{Zn^{2+}(aq)}$ at 298 K. A second half-cell contains $\ce{Fe^{3+}(aq)}$ and $\ce{Fe^{2+}(aq)}$, each at $1.00\ \text{mol dm}^{-3}$. The two half-cells are joined by a salt bridge and an external wire. The $\ce{Fe^{3+}/Fe^{2+}}$ couple has the more positive standard reduction potential.
Part a: What should the electrode in the iron half-cell be, and why? (1 mark) Part b: Which electrode is the negative electrode? (1 mark) Part c: How do electrons travel between the half-cells? (1 mark) Part d: Write the half-equation for the reaction at the positive electrode. (1 mark) Part e: Write the conventional cell notation for this cell, showing every phase boundary and the salt bridge. (2 marks) Predicting whether chlorine oxidises iron(II) ions.
$\ce{Cl2(g) + 2e^- <=> 2Cl^-(aq)}$ $\quad E^\ominus=+1.36\ \text{V}$
$\ce{Fe^{3+}(aq) + e^- <=> Fe^{2+}(aq)}$ $\quad E^\ominus=+0.77\ \text{V}$
Chlorine is bubbled into aqueous iron(II) sulfate under standard conditions.
Part a: Which half-equation proceeds in the forward (reduction) direction? (1 mark) Part b: Calculate $E^\ominus_{\text{cell}}$ for the reaction between chlorine and iron(II) ions, in V. (1 mark) Part c: Write the balanced ionic equation for the reaction, without state symbols. (1 mark) Part d: Identify the oxidising agent. (1 mark) Part e: $E^\ominus_{\text{cell}}$ is positive. Which conclusion can it not support? (1 mark) Combining the dichromate(VI) and sulfite half-equations.
In acidic solution:
$\ce{Cr2O7^{2-} + 14H+ + 6e^- -> 2Cr^{3+} + 7H2O}$
$\ce{SO3^{2-} + H2O -> SO4^{2-} + 2H+ + 2e^-}$
Part a: By what number must the sulfite half-equation be multiplied before the two half-equations are added? (1 mark) Part b: In the simplest balanced overall equation, how many $\ce{H+}$ ions appear on the left-hand side? (1 mark) Part c: In the same equation, how many $\ce{H2O}$ molecules appear on the right-hand side? (1 mark) Part d: Write the overall balanced ionic equation. (1 mark) Part e: State the oxidation number of chromium in $\ce{Cr2O7^{2-}}$. (1 mark) Part f: Identify the oxidising agent. (1 mark) Part g: Identify the reducing agent. (1 mark) Relating $E^\ominus_{\text{cell}}$ to $\Delta G^\ominus$.
A spontaneous cell reaction transfers 3 mol of electrons per mole of reaction as written and has $E^\ominus_{\text{cell}}=+0.48\ \text{V}$. Use $F=9.65\times10^4\ \text{C mol}^{-1}$.
Part a: Calculate $\Delta G^\ominus$ for the reaction, in kJ mol$^{-1}$. (1 mark) Working for part a (1 mark) Part b: State $E^\ominus_{\text{cell}}$ for the reverse reaction, in V. (1 mark) Part c: State $\Delta G^\ominus$ for the reverse reaction, in kJ mol$^{-1}$. (1 mark) Copper deposition below 100% current efficiency.
A steady current of 2.50 A passes through aqueous copper(II) sulfate for 40.0 min, depositing copper at the cathode. Use $F=9.65\times10^4\ \text{C mol}^{-1}$ and $A_r(\ce{Cu})=63.5$.
Part a: Calculate the charge passed, in C. (1 mark) Part b: Calculate the amount of electrons transferred, in mol, to three significant figures. (1 mark) Part c: Calculate the theoretical mass of copper deposited, in g. (1 mark) Part d: Only 92.0% of the charge deposits copper. Calculate the actual mass of copper deposited, in g. (1 mark) Choosing a power source for a delivery truck.
A logistics company is choosing between a hydrogen–oxygen fuel cell and an improved rechargeable lithium-ion battery pack for a long-distance delivery truck that must be back on the road quickly after each stop. The fuel cell takes oxygen from the air.
Part a: Which statement about the fuel cell's emissions is justified? (1 mark) Part b: Which is a genuine limitation of carrying hydrogen as the fuel? (1 mark) Part c: Which is an advantage of improved batteries over older battery types? (1 mark) Part d: Recommend a power source for this truck. Give one advantage and one limitation of each option and justify your choice. (3 marks)