DP Chemistry Questionbank

Magnesium chloride can be electrolysed.

(i) Deduce the half-equations for the reactions at each electrode when molten magnesium chloride is electrolysed, showing the state symbols of the products. The melting points of magnesium and magnesium chloride are 922K and 987K respectively.

(ii) Identify the type of reaction occurring at the cathode (negative electrode).

(iii) State the products when a very dilute aqueous solution of magnesium chloride is electrolysed.

A magnesium half-cell, Mg(s)/Mg²⁺(aq), can be connected to a copper half-cell, Cu(s)/Cu²⁺(aq).

(i) Formulate an equation for the spontaneous reaction that occurs when the circuit is completed.

(ii) Determine the standard cell potential, in V, for the cell. Refer to section 24 of the data booklet.

(iii) Predict, giving a reason, the change in cell potential when the concentration of copper ions increases.

A concentration cell is an example of an electrochemical cell.

(i) State the difference between a concentration cell and a standard voltaic cell.

(ii) The overall redox equation and the standard cell potential for a voltaic cell are:

Zn (s) + Cu²⁺ (aq) → Zn²⁺ (aq) + Cu (s)     E^θ_cell = +1.10 V

Determine the cell potential E at 298 K to three significant figures given the following concentrations in mol dm⁻³:

[Zn²⁺] = 1.00 × 10⁻⁴       [Cu²⁺] = 1.00 × 10⁻¹

Use sections 1 and 2 of the data booklet.

(iii) Deduce, giving your reason, whether the reaction in (b) (ii) is more or less spontaneous than in the standard cell.

An iron rod is electroplated with silver. Which is a correct condition for this process?

A. The silver electrode is the positive electrode.

B. The iron rod is the positive electrode.

C. The electrolyte is iron(II) sulfate.

D. Oxidation occurs at the negative electrode.

Standard electrode potentials are measured relative to the standard hydrogen electrode. Describe a standard hydrogen electrode.

Which statement is correct for the overall reaction in a voltaic cell?

2AgNO₃(aq) + Ni(s) → 2Ag(s) + Ni(NO₃)₂(aq)         E ^θ= +1.06 V

A.     Electrons flow from Ag electrode to Ni electrode.

B.     Ni is oxidized to Ni²⁺ at the cathode (negative electrode).

C.     Ag⁺ is reduced to Ag at the anode (positive electrode).

D.     Ag has a more positive standard electrode potential value than Ni.

Comment on the spontaneity of this reaction by calculating a value for $\mathrm{\Delta }{G}^{\theta }$ using the data given in (b) and in section 1 of the data booklet.

In the electrolysis of aqueous potassium nitrate, KNO₃(aq), using inert electrodes, 0.1 mol of a gas was formed at the cathode (negative electrode).

Which is correct?

Identify, from the table, a non-vanadium species that could convert ${\text{VO}}_2^{+}\text{(aq)}$ to V²⁺(aq).

Identify, from the table, a non-vanadium species that can reduce VO²⁺(aq) to V³⁺(aq) but no further.

Calculate the Gibbs free energy, ΔG ^θ, in kJ, which is released by the corrosion of 1 mole of iron. Use section 1 of the data booklet.

Zinc is used to galvanize iron pipes, forming a protective coating. Outline how this process prevents corrosion of the iron pipes.

Corrosion of iron is similar to the processes that occur in a voltaic cell. The initial steps involve the following half-equations:

Fe²⁺(aq) + 2e^– $\rightleftharpoons$ Fe(s)

$\frac{1}{2}$O₂(g) + H₂O(l) + 2e^– $\rightleftharpoons$ 2OH^–(aq)

Calculate E ^θ, in V, for the spontaneous reaction using section 24 of the data booklet.

Which statement is correct when a zinc spoon is electroplated with silver?

A.  The cathode (negative electrode) is made of silver.

B.  The anode (positive electrode) is the zinc spoon.

C.  The anode (positive electrode) is made of silver.

D.  The electrolyte is zinc sulfate solution.

The electron configuration of copper makes it a useful metal.

Copper plating can be used to improve the conductivity of an object.

State, giving your reason, at which electrode the object being electroplated should be placed.

Calculate the standard cell potential, in $\mathrm{V}$, for the cell at $298 \mathrm{K}$. Use section 24 of the data booklet

Calculate the standard free energy change, $∆{\mathrm{G}}^{⦵}$, in $\mathbf{kJ}$, for the cell using sections 1 and 2 of the data booklet.

Write the balanced equation for the reaction in this voltaic cell.

Predict, giving a reason, how an increase in temperature affects the potential of this cell.

Calculate the cell potential for $0.0100 \mathrm{mol} {\mathrm{dm}}^{-3} {\mathrm{Mg}}^{2+}\left(\mathrm{aq}\right)$ and $0.800 \mathrm{mol} {\mathrm{dm}}^{-3} {\mathrm{Ni}}^{2+}\left(\mathrm{aq}\right)$ at $298 \mathrm{K}$. Use sections 1, 2 and 24 of the data booklet.

Calculate the cell potential, in V, when the standard iodine and manganese half-cells are connected.

State and explain the products of electrolysis of a concentrated aqueous solution of sodium chloride using inert electrodes. Your answer should include half-equations for the reaction at each electrode.

What are the products when an aqueous solution of copper(II) sulfate is electrolysed using inert graphite electrodes?

Predict, giving a reason, the direction of movement of electrons when the standard nickel and manganese half-cells are connected.

What are the products when concentrated aqueous copper (II) chloride is electrolysed using platinum electrodes?

What would be the electrode potential, E^⦵, of the Mn²⁺(aq)|Mn (s) half-cell if Fe³⁺(aq)|Fe²⁺(aq) is used as the reference standard?

Mn²⁺ (aq) + 2e⁻ $\rightleftharpoons$ Mn (s)           E^⦵ = −1.18 V

Fe³⁺ (aq) + e⁻ $\rightleftharpoons$ Fe²⁺(aq)          E^⦵ = +0.77 V

A.  −1.95 V

B.  −0.41 V

C.  +0.41 V

D.  +1.95 V

What happens to the mass of each copper electrode when aqueous copper(II) sulfate solution is electrolysed?

A voltaic cell is set up between the Fe²⁺(aq) | Fe (s) and Fe³⁺ (aq) | Fe²⁺ (aq) half-cells.

Deduce the equation and the cell potential of the spontaneous reaction. Use section 24 of the data booklet.

Calculate the cell potential using section 24 of the data booklet.

Calculate the Gibbs free energy change, ΔG^⦵, in kJ, for the cell, using section 1 of the data booklet.

Two cells undergoing electrolysis are connected in series.

If $x$ g of silver are deposited in cell 1, what volume of oxygen, in dm³ at STP, is given off in cell 2?

A_r(Ag) = 108; Molar volume of an ideal gas at STP = 22.7 dm³ mol⁻¹

A.    $\frac{x}{108}\times \frac{1}{4}\times 22.7$

B.    $\frac{x}{108}\times 4\times 22.7$

C.    $\frac{x}{108}\times \frac{1}{2}\times 22.7$

D.    $\frac{x}{108}\times 2\times 22.7$

What are the major products of electrolysing concentrated aqueous potassium iodide, KI(aq)?

Calculate the cell potential, in V, using section 24 of the data booklet.

Determine the loss in mass of one electrode if the mass of the other electrode increases by 0.10 g.

Calculate the standard electrode potential, in V, for the BrO₃⁻/Br⁻ reduction half‑equation using section 24 of the data booklet.

The change in the free energy for the reaction under standard conditions, ΔG^Θ, is −514 kJ at 298 K.

Determine the value of E^Θ, in V, for the reaction using sections 1 and 2 of the data booklet.

Deduce the gas formed at the anode (positive electrode) when graphite is used in place of copper.

Consider the following standard electrode potentials:

Which species will react with each other spontaneously under standard conditions?

A.  Zn²⁺(aq) + Pb (s)

B.  Pb²⁺(aq) + Br₂(l)

C.  Zn (s) + Br⁻(aq)

D.  Pb (s) + Br₂ (l)

Which aqueous solutions produce oxygen gas during electrolysis?

I.   Dilute CuCl₂(aq) with inert electrodes
II.  Dilute FeSO₄(aq) with inert electrodes
III. Dilute CuCl₂(aq) with copper electrodes

The standard electrode potentials are provided in the table:

A.  I and II only

B.  I and III only

C.  II and III only

D.  I, II and III

The standard electrode potential of zinc can be measured using a standard hydrogen electrode (SHE).

Draw and annotate the diagram to show the complete apparatus required to measure the standard electrode potential of zinc.

Consider the standard electrode potentials:

Cr³⁺ (aq) + 3e⁻ $\rightleftharpoons$ Cr (s)       E^Θ = −0.74 V

Hg²⁺ (aq) + 2e⁻ $\rightleftharpoons$ Hg (l)      E^Θ = +0.85 V

What is the cell potential, in V, for the voltaic cell?

2Cr (s) + 3Hg²⁺ (aq) → 3Hg (l) + 2Cr³⁺ (aq)

A.   −1.59

B.   +0.11

C.   +1.07

D.   +1.59

A student electrolyzed aqueous iron(II) sulfate, FeSO₄ (aq), using platinum electrodes. State half-equations for the reactions at the electrodes, using section 24 of the data booklet.

Calculate the standard Gibbs free energy change, ΔG^Θ, in J, of the redox reaction in (ii), using sections 1 and 24 of the data booklet.

E^Θ (BrO₃⁻ / Br⁻) = +1.44 V

In the electrolysis apparatus shown, 0.59 g of Ni is deposited on the cathode of the first cell.

What is the mass of Ag deposited on the cathode of the second cell?

A.  0.54 g

B.  0.59 g

C.  1.08 g

D.  2.16 g

What are the products when dilute aqueous copper (II) nitrate is electrolysed using platinum electrodes?

E^⦵ (Cu | Cu²⁺) = –0.34 V.

Which E^⦵ value, in V, for the reaction Mn (s) + Zn²⁺(aq) → Mn²⁺(aq) + Zn (s) can be deduced from the following equations?

Mn (s) + 2Ag⁺(aq) → Mn²⁺(aq) + 2Ag (s)     E^⦵ = 1.98 V

Zn (s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu (s)        E^⦵ = 1.10 V

Cu (s) + 2Ag⁺(aq) → Cu²⁺(aq) + 2Ag (s)      E^⦵ = 0.46 V

A.  0.42

B.  1.34

C.  2.62

D.  3.54

Calculate the free energy change, ΔG^⦵, in kJ, of the cell reaction. Use sections 1 and 2 of the data booklet.

This cell causes the electrolytic reduction of water on the steel. State the half-equation for this reduction.

Calculate the standard potential, in V, of a cell formed by magnesium and steel half-cells. Use section 24 of the data booklet and assume steel has the standard electrode potential of iron.

Iron(II) is oxidized by bromine.

2Fe²⁺ (aq) + Br₂ (l) $\rightleftharpoons$ 2Fe³⁺ (aq) + 2Br⁻ (aq)

Calculate the E^⦵_cell, in V, for the reaction using section 24 of the data booklet.

Determine, giving a reason, if iodine will also oxidize iron(II). 

An aqueous solution of silver nitrate, AgNO₃ (aq), can be electrolysed using platinum electrodes.

Formulate the half-equations for the reaction at each electrode during electrolysis.

Cathode (negative electrode):

Anode (positive electrode):

Calculate the standard electrode potential, in V, when the Fe²⁺ (aq) | Fe (s) and Cu²⁺ (aq) | Cu (s) standard half-cells are connected at 298 K. Use section 24 of the data booklet.

Calculate ΔG^θ, in kJ, for the spontaneous reaction in (f)(i), using sections 1 and 2 of the data booklet.

Predict, giving a reason, whether the reduction of ReO₄⁻ to [Re(OH)₂]²⁺ would oxidize Fe²⁺ to Fe³⁺ in aqueous solution. Use section 24 of the data booklet.

A scientist wants to investigate the catalytic properties of a thin layer of rhenium metal on a graphite surface.

Describe an electrochemical process to produce a layer of rhenium on graphite.

Which is not a requirement of the standard hydrogen electrode (SHE)?

A. V = 1 dm³

B. p(H₂) = 100 kPa

C. use of platinum as the electrode material

D. [H₃O⁺] = 1 mol dm⁻³

What are the products when concentrated KBr (aq) is electrolyzed?

Consider the following table of standard electrode potentials.

Which is the strongest oxidizing agent?

A. Pb²⁺

B. Pb

C. Al³⁺

D. Al

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

Calculate the standard Gibbs free energy change, ΔG^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.

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

Electrode number (on diagram):

Name of gas: 

Deduce the half-equation for the formation of the gas identified in (c)(iii).

Three cells with platinum electrodes are connected in series to a DC power supply.

What is the ratio of moles formed at each cathode (negative electrode)?

Deduce the half-equations for the reactions occurring at the electrodes.

Anode (negative electrode):

Cathode (positive electrode):