This set of Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Electrochemistry – Batteries”.
1. A battery is an arrangement of electrolytic cells.
Explanation: A battery is not an arrangement of electrolytic cells, but an arrangement of electrochemical cells. An electrochemical cell is one which converts chemical energy into electrical energy whereas an electrolytic cell is one which converts electrical energy into chemical energy. Since batteries convert chemical energy to electrical energy, it is an arrangement of electrochemical cells.
2. Which of the following is not a requirement for a useful battery?
a) It should be light and compact
b) It should have a reasonable life span
c) It should ideally have a constant voltage throughout its lifespan
d) It should supply Alternating Current(AC)
Explanation: A useful battery is expected to be light and compact to be easily transported. It is expected to have a reasonable lifespan to justify its usage. Its voltage should not vary appreciably during usage so that it doesn’t adversely affect the circuit it is used in. A battery supplies Direct Current(DC) and not Alternating Current(AC).
3. Which of the following statements is true regarding a primary cell?
a) The electrode reactions can be reversed
b) It can be recharged
c) An example of a primary cell is a mercury cell
d) An example of a primary cell is a nickel-cadmium storage cell
Explanation: A primary cell is one in which the electrode reactions occur only once and cannot be reversed by applying electrical energy. Therefore, primary cells cannot be recharged. A mercury cell is an example of a primary cell, whereas a nickel-cadmium storage cell is an example of a secondary cell.
4. Secondary cells are also called storage cells.
Explanation: Secondary cells are those cells in which the electrode reaction can be reversed by applying an electrical energy. Therefore, they can be used to store electrical energy. So, they are also known as storage cells.
5. Which of the following is used as an anode in a dry cell?
c) Mercury(II) oxide
Explanation: A dry cell is constructed using zinc and graphite. It consists of a zinc cylinder through whose centre passes a graphite rod. The zinc cylinder acts as an anode, whereas the graphite rod acts as a cathode.
6. Why do leak proof dry cells have an iron or steel sheet covering the zinc cylinder?
a) It increases the potential difference between the anode and cathode
b) It acts as a barrier around the zinc cylinder which can develop holes during use
c) It makes it waterproof
d) It prevents the leakage of current
Explanation: In a dry cell, zinc loses electrons and the zinc ions dissolve into the electrolyte. As a result, the zinc cylinder of the dry cell develops holes as it is used. To prevent the leakage of electrolyte through these holes, an iron or steel sheet is used to cover the cylinder.
7. Which of the following is the electrolyte used in a dry cell?
a) Ammonium chloride
b) Manganese dioxide
c) Potassium hydroxide
d) Sulphuric acid
Explanation: The electrolyte in a dry cell is ammonium chloride in the form of a moist paste placed next to the zinc anode. In some dry cells marketed as “heavy-duty”, the ammonium chloride is replaced by zinc chloride.
8. What is the role of manganese dioxide in a dry cell?
a) It acts as an electrolyte
b) It acts as the cathode
c) It acts as an anode
d) It acts as a depolariser
Explanation: In a dry cell, in the remaining space between the electrolyte and the graphite cathode, a second paste consisting of ammonium chloride and manganese dioxide is applied. The manganese dioxide acts as a depolariser as it helps to prevent the build-up of hydrogen gas bubbles.
9. What is the final oxidation state of manganese after the electrochemical reactions in a dry cell?
Explanation: In a dry cell, in the cathode reaction, manganese dioxide(MnO2) is reduced to form manganese oxide-hydroxide(MnO(OH)). In this process, the oxidation state of manganese changes from +4 to +3. Hence the final oxidation state of manganese is +3.
10. Which of the following scientists invented the first dry cell?
a) Carl Gassner
b) Nikola Tesla
c) Antione Lavoisier
d) Georges Leclanché
Explanation: In the year 1886, Carl Gassner obtained a German patent on a variant of the wet Leclanché cell, which can be known as the dry cell because it did not have a liquid electrolyte. Instead, a mixture of ammonium chloride and plaster of paris was used.
11. What is the final product that zinc forms during the functioning of a mercury cell?
Explanation: A mercury cell consists of a zinc anode and a mercury(II) oxide cathode. Potassium hydroxide is used as the electrolyte. In the electrochemical reaction, zinc is oxidised to become zinc oxide(ZnO) whereas mercury(II) oxide is reduced to elemental mercury.
12. Which of the following appliances would not use sodium hydroxide as an electrolyte in their mercury cells?
b) Hearing aids
c) Electronic watches
d) Photographic cameras with a flash
Explanation: Sodium hydroxide cells have nearly constant voltage at low discharge currents whereas potassium hydroxide cells provide a constant voltage at high discharge currents. Therefore, sodium hydroxide cells are ideal for calculators, hearing aids and electronic watches whereas potassium hydroxide cells are ideal for photographic cameras with a flash.
13. Which of the following is the voltage output of a mercury cell?
Explanation: Mercury batteries use a reaction between mercuric oxide and zinc in an alkaline electrolyte to produce electricity. Its voltage during discharge is a constant 1.35V. The common dry cell, on the other hand, provides a voltage of 1.5V.
14. Which of the following statements is not true with respect to a lead storage cell (or a lead-acid battery)?
a) The electrolyte used is an aqueous solution of sulphuric acid
b) The anode is made up of lead
c) The cathode is made up of lead(IV) oxide
d) It is a primary cell
Explanation: A lead storage cell is a secondary cell which has a grid of lead packed with finely divided spongy lead for an anode and a grid of lead packed with lead(IV) oxide for a cathode. The electrolytic solution used in a lead-acid battery is an aqueous solution of sulphuric acid.
15. Which of the following products are formed when a lead storage battery is discharged?
Explanation: During the working of the lead storage battery, PbSO4 is formed at both the electrodes and sulphuric acid is used up. At the anode, Pb is oxidised to form PbSO4 and at the cathode, PbO2 is reduced to form PbSO4.
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