Test: Battery & Corrosion - NEET MCQ

(b) Electrons flow from anode to cathode-correct.

(a) A typical 12V battery consists of six cells connected in series each cell providing a potential of about 2V -correct
(b) No separation of cathodic and anodic compartment, species being in solid state -correct
(c) During recharging, E° < 0, thus ΔG° > 0-correct.

In lead-acid storage battery, specific gravity of H₂SO₄ changes and water is to be added periodically. In maintenance free battery calcium-containing lead alloy that prevents the electrolytic decomposition of H₂O. These batteries are sealed and no maintenance is required

I. Mercury battery has anode made of zinc and cathode is a steel vessel in contact with HgO in alkaline medium of KOH and Zn(OH)₂.

Net reaction does not involve OH^- , hence emf is independent of [OH^-].
II. In nickel, cadmium battery, net reaction is

Since, (OH^-) species are in solid state, hence emf is independent of (OH^-).
III. Alkaline dry cell is a modified version of the Leclanche cell. Net reaction is

Thus, emf is independent of (OH^-).

I. Primary Leclanche cell.
Secondary Lead-storage
Flow battery Fuel-cell
II. True
III. True

In fuel-cell, reactions are not contained within the cell but are supplied from external source. (It is used as a source of electric power in space vehicles).

Pipes are made of Iron. Iron can be oxidised toFe²⁺.
Fe → Fe²⁺ + 2e^-
but when connected to Mg, which is more electropositive that Fe, Mg is oxidised to Mg²⁺ and in turn reduces Fe²⁺ (rust) to Fe

It is called cathodic protection but at the cost of Mg (sacrified anode).

In presence of moisture, rate of corrosion of metal is enhanced.

More noble metal is cathode and is protected from rusting by active metal which is anode.

I. Temperature affects corrosion. However, solubility of dissolved gases decreases with rise in temperature.
II. In acidic medium, pH < 7 (acid rain), enhances corrosion

In basic medium, pH > 7
Fe²⁺ changes to Fe (OH₂) and then to Fe(OH₃)(s) (Fe₂O₃ - rust)
III. Impure metals set up their own electrochemical cells and thus, corrosion is enhanced.
IV. Conc. HNO₃ forms an oxide protective layer on the surface of a metal. When metal (as Al) reacts with cone. HNO₃, there is reaction but it ceases due to formation of an oxide (Al₂O₃) layer. Thus, HNO₃ can be stored in Al vessel.

During discharge, sulphuric acid is consumed as :

Note Pb is oxidised to Pb²⁺ (asPbSO₄)PbO₂(+4) is reduced to Pb²⁺ (as PbSO₄) and specific gravity of H₂SO₄ decreases.

(a) In oxidised state, shine of the metal is furnished, thus, corrosion is the oxidative deterioration of a metal. (b) A mini-cell is set up at the surface at which corrosion takes place.

Reaction is spontaneous-correct.
(c) Impurities also react with active metals by making own cells. Thus, correct.

Acid rain causes corrosion of metals. Even Cu, Ag and Pb are corroded.

In the anodic reaction, the metal that is more easily oxidised loses electrons to produce metal ions. In case (a), zinc (more electropositive than Fe) is oxidised. In case (b), iron (more electropositive than Cu is oxidised).
In the cathodic reaction, oxygen gas which is dissolved in a thin film of water on the metal is reduced to OH^-.
Thus, rusting of iron does not take place in (a) but it is in (b).
Fe²⁺ and OH^- ions from the half-reactions initiate these further reactions

Oxidation at Cr electrode (anode)

Thus, oxidation half-cell is

reduction at Fe electrode (cathode)

Thus, reduction half-cell is

Two half-cells are joined by a salt-bridge

In a dry-cell battery (also called Leclanche cell)
Anode Outer cover (cylindrical) is made of zinc. Oxidation takes place at anode.

Cathode Graphite (carbon) rod in a paste of MnO₂ and carbon black.
Electrolyte Paste of NH₄CI/ZnCI₂ (with starch binder) Reduction takes place.

Thus, I, II and III are correct.

Fe can be protected by making a layer of zinc on it. It is called galvanisation. At the cost of Zn (which is oxidised), Fe is protected.

Thus, Fe which is cathode is protected.
It is called cathodic protection and active metal is thus, sacrified anode.

If (a) and (d) are combined,
E° = + 0.89V, ΔG° < 0 
and E°_cell is independent of (OH^-).

To make cell reaction spontaneous, E° _cell > 0

Thus, battery emf is independent on [OH^-]
 ΔG° = - nF E°_cell 
= - 2 x 96500x 1.27
= -245100 J 
= -245.1 kJ
Thus, energy obtained per mole of Ni₂O₃ consumed i s -245.1 kJ.

Al metal is used to remove Ag₂S.

NaHCO₃ in hot water is used as electrolyte and dissolves displaced S^2-. 

Al metal is used to remove Ag₂S.

NaHCO₃ in hot water is used as electrolyte and dissolves displaced S^2-.

In battery H₂SO₄ ionises as

In battery H₂SO₄ ionises as



 

ΔG°= -nFE° = -2 x 96500 x 1.5544 J
= -3 x 10⁵ 
= x x 10^y
Thus,  x + y = 8