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Right choice is (b) +3

The BEST 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.

The correct choice is (b) False

For EXPLANATION I WOULD say: 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.

The correct option is (C) It DEPENDS on the SOLVATION of ions PRESENT in solution

To ELABORATE: Conductivity of a solution is inversely proportional to the size of the ions present in it, the viscosity of the solution and the solvation of the ions in the solution. Conductivity increases with temperature as it can cause an increase in the number of ions in solution.

The correct choice is (a) Galvani and VOLTA

Easiest explanation: Electrochemical CELLS are also CALLED galvanic or voltaic cells, after the names of Luigi Galvani and ALESSANDRO Volta who were the first to perform experiments on the conversion of CHEMICAL energy into electrical energy.

Right option is (d) It keeps the electrolyte in semi-solid phase and prevents it from mixing with the TWO half-cell solutions

Easiest explanation: The salt bridge connects the two half-cell solutions to complete the circuit of the ELECTROCHEMICAL cell. The electrolytes of the salt bridge are GENERALLY PREPARED in agar-agar or gelatin so that the electrolytes are kept in a semi-solid phase and do not mix with the half-cell solutions and interfere with the electrochemical reaction.

The CORRECT ANSWER is (a) Ammonium CHLORIDE

To explain I would SAY: 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.

Right choice is (c) COPPER

Explanation: Magnesium and ZINC are highly active. Hence, they corrode at a faster rate than iron. Iron UNDERGOES rusting in the presence of oxygen and moisture. Copper, a noble metal that OCCURS naturally in its elemental form, is ALMOST totally impervious to corrosion.

Correct answer is (d) Zn and Cu

The best I can explain: The two ELECTRODES that are used in a Daniell cell are ZINC (as anode) and COPPER (as cathode) electrodes which are dipped in a solution containing its own IONS, generally zinc sulphate and copper sulphate.

Right answer is (C) Mercury(II) oxide

The explanation is: 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.

Right option is (a) True

To ELABORATE: Electrolysis is a PROCESS of passing a DIRECT current through the ELECTRODES to achieve a chemical REACTION. It is not possible to achieve a chemical reaction when the chosen electrolyte is in a solid-state.

The correct answer is (a) True

Best explanation: According to KOHLRAUSCH’s LAW, the equivalent conductivity of an electrolyte at infinite DILUTION is the sum of TWO values one depending UPON the cation and the other upon the anion. Therefore, it can be used to calculate the limiting equivalent conductance for weak electrolytes.

Right CHOICE is (B) 0.49 V

Explanation: GIVEN, equilibrium constant KC = 4 × 10^16

E° (cell) = \(\frac{0.059}{2}\)log10 Kc

E°(cell) = \(\frac{0.059}{2}\)log10 (4 × 10^16)=0.49V.

The correct option is (B) False

Explanation: An electrochemical cell can convert ELECTRICAL energy to CHEMICAL energy and can ALSO convert electrical energy to chemical energy. There are TWO types of electrochemical cells- Galvanic cell and Electrolytic cell.

Right answer is (a) True

Explanation: Magnesium and zinc are often used as sacrificial metals. Sacrificial PROTECTION means covering the iron SURFACE with a layer of METAL which is more active (electropositive) than iron and thus prevents the iron from losing ELECTRONS and GETTING oxidised.

The correct answer is (a) True

The explanation: The most common example of corrosion is the RUSTING of IRON. Rust is hydrated ferric oxide, Fe2O3.xH2O. Rust is formed by the reaction of iron and OXYGEN in the presence of WATER or air MOISTURE.

Right CHOICE is (d) William Grove

For explanation I would SAY: The first fuel cell was conceived by SIR William Robert Grove in 1839. He mixed HYDROGEN and oxygen in the presence of an electrolyte and produced electricity and water. The fuel cell he made used similar materials to today’s phosphoric acid fuel cell.

Right choice is (b) It acts as a BARRIER around the zinc cylinder which can develop holes during use

The 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.

The correct choice is (a) True

To elaborate: EMF of a cell is equal to the maximum potential difference across its electrodes, which OCCURS when no CURRENT is DRAWN through the cell. It can also be defined as the net voltage between the oxidation and reduction half-reactions.

Correct choice is (d) Light

The best explanation: Rust is a general TERM for a SERIES of iron oxides, usually, reddish-brown oxides, formed by the reaction of iron with oxygen in the presence of water or MOISTURE. Water is usually present in the form of water vapour and oxygen is always present in the normal atmosphere. The oxygen needs moisture as a catalyst and reactant to accelerate the reaction, so in the ABSENCE of moisture, iron won’t rust.

Right option is (d) It is a primary CELL

The best 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.

The correct CHOICE is (a) Copper metal

For explanation: In the electrolysis of AQUEOUS CuSO4, Cu^2+, SO4^2+, H^+ and OH^–are the ions formed after DISSOCIATION. Copper ions have much HIGHER reduction potential than water. Hence, these ions are EASILY reduced and deposited as Cu at the cathode.

Correct option is (d) CsCl

Explanation: On MOVING down a group, the ATOMIC size of the ELEMENTS increases and so their covalent CHARACTER also DECREASES. Thus, CsCl, being the least covalent compound will readily give its ions in its fused state. Therefore, CsCl has the maximum value of equivalent conductance in its fused state.

The correct OPTION is (c) 3.73

For explanation I would say: GIVEN, potential of hydrogen gas ELECTRODE = -0.22 V

Electrode REACTION: H^+ + e^– → 0.5 H2

Applying Nernst equation,

E(H+/H₂) = E°(H+/H2) – 0.059 LOG (1/ [H^+])

E°(H+/H₂) = 0 for hydrogen gas electrode

-0.22 = 0.059 log H^+

-0.22 = -0.059pH

pH= 3.73.

The correct CHOICE is (a) KOH

Explanation: The GENERAL design of the H2-O2 fuel cell consists of porous carbon electrodes containing suitable catalysts (generally finely divided platinum and PALLADIUM) incorporated in them. CONCENTRATED KOH or NaOH solution is placed between the electrodes to ACT as the electrolyte.

The CORRECT choice is (C) Conductance

The explanation: An ADDITIVE property is a property which is equal to the sum of corresponding properties of its constituent atoms. In the given list, viscosity, surface tension and volume are not additive properties since it does not depend on the INTERACTIONS of molecules whereas conductance does. Therefore, conductance is an additive property.

The correct option is (d) 9.44 × 10^-3 M

Easiest explanation: The ELECTRODE reaction is Zn^2+ + 2e^– → Zn

The number of electrons TRANSFERRED, n= 2

Applying Nernst equation, we get E(Zn+2/Zn) = E°(Zn+2/Zn) – \(\FRAC{0.059}{2}\)LOG (1 / [Zn^2+])

[Zn^2+] = \(\frac{98}{100}\) × n = 0.98n M

-0.56 = -0.5 – \(\frac{0.059}{2}\)log (1 / 0.98n)

n= 9.44 × 10^-3 M.

The correct choice is (b) Cell potential is an intensive PROPERTY

Explanation: Cell potential is an intensive property as it is independent of the amount of material present. Gibbs FREE energy is defined for an ELECTROCHEMICAL cell and is an extensive property as it depends on the quantity of the material.

The correct choice is (d) ZnSO4

For explanation I would say: A salt bridge is a device used to CONNECT the oxidation and reduction half-cells of a galvanic cell (a type of ELECTROCHEMICAL cell). Strong electrolytes are generally used to make the salt BRIDGES in electrochemical cells. Since ZnSO4 is not a strong ELECTROLYTE, it is not used to make salt bridges.

Right choice is (a) Anode to cathode externally

The BEST I can explain: An electrolytic cell is a TYPE of electrochemical cell. An electrolytic cell converts ELECTRICAL ENERGY into chemical energy. Electrons FLOW from anode to cathode through the external supply in an electrolytic cell. In the solution, only ions flow and not the electrons.

The correct choice is (a) The electrochemical cell behaves like an electrolytic cell

The EXPLANATION is: In an electrochemical cell, when an opposing EXTERNALLY potential is APPLIED and increased slowly, the reaction continues to take place. When the external potential is EQUAL to the potential of the cell, the reaction stops. Once the externally applied potential is greater than the potential of the cell, the reaction goes in the opposite direction and the cell behaves like an electrolytic cell.

Correct choice is (c) HYDROGEN gas

The BEST explanation: Na2SO4 dissociates into Na^+ and SO4^2- ions in the electrolysis of AQUEOUS Na2SO4. Na^+ has much lower reduction potential than water and hence Na^+ ions are not reduced at the CATHODE. Instead, reduction of water occurs giving out hydrogen gas at the cathode.

The CORRECT choice is (a) 5.08

Best explanation: Given,

Standard oxidation potential of Ni/Ni^2+ electrode, E°OP = 0.3 V,

Ni → Ni^2+ + 2E

2H^+ + 2e → H2

E°cell = E° (OP) + E° (RP)

E° (cell) = 0.3 + 0.0 = 0.3 V

According to NERNST equation, E (cell) = E°(cell) + \(\frac{0.059}{2}\) log10([H^+]^2 / [Ni]^+2)

0 = 0.3 + \(\frac{0.059}{2}\)log10([H^+]^2)

-log ([H^+]) = 5.08

pH = 5.08.

Correct answer is (c) E° (M2+/M) + 0.0315log10 (1 / [M]^+2)

The best I can explain: Given, Temperature T = 45°C

We know, n (number of electrons transferred) = 2

According to Nernst EQUATION, E(M2+/M) = E° (M2+/M) +2.303\(\frac{RT}{nF}\)log10 (M / [M]^+2)

Concentration of [M] is taken to be 1

The equation becomes: E° (M2+/M) +2.303 \(\frac{RT}{nF}\)log10 (1/[M]^+2)

E(M2+/M) = E° (M2+/M) +2.303 × \(\frac{8.314 \times 318}{2 \times 96500}\)log10 (1 / [M]^+2) =E° (M2+/M) + 0.0315log10 (1 / [M]^+2).

Correct choice is (c) An example of a PRIMARY cell is a mercury cell

To elaborate: 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.

Correct answer is (d) Heating

The best I can explain: Galvanization is the process of coating iron with zinc to prevent its oxidation. Anti-rust solutions are ALKALINE phosphate and alkaline chromate solutions. The alkalinity prevents the availability of hydrogen ions. Cathodic protection is the process of connecting the iron object to be PROTECTED to a more ACTIVE METAL either directly or through a wire.

Right option is (c) The reactions TAKING place are non-spontaneous

For explanation I would say: Galvanic cells are used to convert CHEMICAL energy into electrical energy. TWO electrodes are usually set up in two separate beakers. The electrolytes taken in the two beakers are different. Galvanic cells are based upon spontaneous REDOX reactions. A salt BRIDGE is used to set up this cell.

Correct OPTION is (b) Photovoltaic cell

To elaborate: A VOLTAIC or Galvanic cell is a type of electrochemical cell that CONVERTS chemical ENERGY into electrical energy. Photovoltaic cells are used to convert light energy into electrical energy. An Electrolytic cell is a type of electrochemical cell that converts electrical energy into chemical energy. A fuel cell is an electrochemical cell that converts the chemical energy of a fuel and an oxidizing agent into ELECTRICITY.