MC test: Electrochemistry, rechargeable batteries & fuel cells

Multiple choice test on C.6 Electrochemistry, rechargeable batteries & fuel cells

Use the following 'quiz' to test your knowledge and understanding of this sub-topic. As this relates to a sub-topic on the options you may need access to the IB data booklet.

If you get an answer wrong, read through the explanation carefully to learn from your mistakes.

Which describes a secondary cell?

All cells have an internal resistance. A secondary cell is one in which the electrochemical reaction taking place on the cell can be reversed by applying an external source of electricity.

 

What is the cathode (+) made of in a lead-acid battery?

The anode (−) is made of lead and the cathode (+) is made of PbO2.

 

Which statement explains why a lead-acid battery may need topping up with distilled water occasionally.

Some batteries are now sealed and do not need topping up. The loss of hydrogen and oxygen caused by electrolysis of the sulfuric acid electrolyte can cause the electrolyte level to drop below part of the surface of the electrodes and make the sulfuric acid more concentrated which makes the battery less efficient.

 

Under standard conditions a lead-acid cell has a voltage of about 2.1 V and yet a car battery typically has 12 V. Which statement describes how this is achieved.

Increasing the amount of materials to construct a single cell does increases the power but not the voltage. Changing the conditions from non-standard will have a small, but insignificant, affect on the voltage. Connecting the cells in series gives a total voltage equal to the sum of the individual component cells.

 

Which electrolyte is typically used in a nickel-cadmium cell?

Ni-Cd cells have an alkaline aqueous electrolyte.

 

Which will cause the voltage of the following reaction to increase?

Fe(s)  +  Sn2+(aq)  ⇄   Fe2+(aq)  +   Sn(s)  E⦵ = 0.31 V

Only changing the concentrations of the solutions will affect the position of this heterogeneous equilibrium. It will move to the product side, and thus produce a higher voltage, if [Sn2+(aq)] is increased or if [Fe2+(aq)] is decreased.

 

What does nF collectively represent in the Nernst equation?

F is the Faraday constant which has the unit of charge in coulombs per mole, i.e. C mol−1. n is the number of electrons involved in the change of oxidation state (e.g. it is 2 for Cu2+(aq) + 2e− → Cu(s)) so nF is the molar charge for the reaction occurring.

 

Which is the half-equation for the reaction that occurs at the cathode in an acidic hydrogen fuel cell?

Reduction occurs at the cathode and in acidic solution oxygen reacts with H+ ions.

 

Which expression gives the thermodynamic efficiency of a fuel cell?

The thermodynamic efficiency compares the total amount of energy available to do work (ΔG) with the total enthalpy change for the reaction (ΔH).

 

Which statement is correct concerning the zinc concentration cell: Zn(s)/Zn2+(aq, 0.1 mol dm−3) ΙΙ Zn(s)/Zn2+(aq, 1.0 mol dm−3) when it is operating?

The zinc in the Zn(s)/Zn2+(aq, 0.1 mol dm−3) half-cell will be oxidized (so it forms the anode) and the zinc ions in the Zn(s)/Zn2+(aq, 0.1 mol dm−3) half-cell will increase.

 

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