Chemistry #expch001 Important Questions
Ch. 5. Electrochemistry #expch_005
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- Which of the following element act as an inert electrode
a)Cu
b)Ag
c)Pt
d)None
Answer: C
Explanation
usually platinum works as an inert electrode. An inert electrode means an electrode that doesn’t participate in the chemical reaction. It is a metal submerged in an aqueous solution that transfers electrons rather than exchanging ions with the aqueous solution. Therefore Pt acts as an inert electrode.
Video Explanation
- If electricity is passed through a CuSO4 solution by using a Pt electrode then which of the following possible change occurs?
a) H2 is deposited at the cathode
b) Colour of the solution becomes fade
c) Cu is deposited at an anode
d) All are possible
Answer: B
Explanation
The blue colour of aqueous copper sulphate fades when it is electrolysed using platinum electrodes.
In the aqueous solution, copper sulphate dissociates into its respective ions. On passing electric current, the copper ions (cations) move towards the cathode and get deposited as copper. Simultaneously, the sulphate ions (anions) move towards the anode. So, blue colour of the solution disappears.
Video Explanation
00:00:42
- The greater value of standard reduction potential greater will be the tendency
a) To get oxidized
b) To get reduced
c) To accept electrons
d) Both B and C
Answer: D
Explanation
The reduction potential of a species is its tendency to gain electrons and get reduced. It is measured in millivolts or volts. Larger positive values of reduction potential are indicative of a greater tendency to get reduced.
Video Explanation
- What is the value of universal gas constant in Nernst equation when the potential is given in volts?
a) 8.314 J mol-1K-1
b) 0.0821 L atm mol-1K-1
c) 8.205 m3 atm mol-1K-1
d) 1.987 cal mol-1K-1
Answer: A
Explanation
The universal gas constant is denoted by R and is expressed in units of energy per temperature per mole. Since volts is the SI-Unit of potential, R must also be taken in SI-Units which is 8.314 J mol^-1K^-1.
Video Explanation
- Which of the following cell is not rechargeable?
a) Lead storage battery
b) Silver oxide cell
c) Fuel cell
d) Ni-Cd cell
Answer: B
Explanation
- Primary cells: It is a cell that once it has been discharged, cannot be recharged. Primary cells are called as dry cells because they have solid or molten electrolyte. Secondary cells (storage cell): It is the one that can be electrically recharged after use to their original pre-discharge condition. Silver oxide is primary cell while rest of all are secondary cells.
- Silver oxide cell is a small and primary cell that keeps a stable discharge with a high capacity. The first silver oxide battery (which is a combination of multiple silver oxide cells) was developed by Andre in the 1930s.
Video Explanation
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- Molten KCl conducts electricity due to the presence of
a) Free ions
b) Free molecules
c) Free Electrons
d) Atoms of K and Cl
Answer: A
Video Explanation
- The degree of dissociation of week electrolyte increases as
a) Pressure Increases
b) Dilution decreases
c) Dilution increases
d) None
Answer: C
Explanation
- When more amount of solvent is added to the solution, it helps in dissociating the molecules into ions of a weak electrolyte. Thus, degree of dissociation of weak electrolyte increases upon dilution.
Video Explanation
- What is the pH of HCl solution when the hydrogen gas electrode shows a potential of -0.22 V at standard temperature and pressure?
a) 2.17
b) 2.98
c) 3.73
d) 3.14
Answer: C
Explanation
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.
Video Explanation
- Which of the following is true in the case of the Zn-Cu cell?
a) The flow of electrons takes place from copper to zinc
b) E0 red of the copper electrode is less than that of a zinc electrode
c) Zinc acts as an anode and copper as a cathode
d) All are correct
Answer: C
Explanation
Zn-Cu cell construction is of galvanic where zinc acts as anode and copper as cathode with less redox potential than zinc electrode as flow of electron takes place from copper to zinc
Video Explanation
- Faraday’s laws of electrolysis will fail when
a) Temperature is increased
b) Inert electrodes are used
c) A mixture of electrolytes is used
d) In none of these cases
Answer: D
Explanation
- Faraday’s I Law of Electrolysis: When an electrolyte, either in molten state or solution state is electrolyzed, the amount of substance (m) deposited or dissolved at electrodes is directly proportional to the quantity of electricity (Q) passed through the electrolyte.
- Mathematically,
- m ∝ Q
- or
- m = eQ
- where, e = electrochemical equivalent
- Since e = E/F & Q = I.t
- We can also rewrite the equation as:
- m = E.I.t/F Faraday’s II Law of Electrolysis: If the same quantity of electricity is passed through different electrolytic cells, connected in series containing different electrolytic solutions or melts, the amounts of substances deposited or liberated or dissolved are directly proportional to their equivalent weights.
- Mathematically, m1/m2 = E1/E2
Video Explanation
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- The equilibrium constant for a cell reaction, Cu(g) + 2Ag+(aq) → Cu2+(aq) + 2Ag (s) is 4 × 1016. Find E° (cell) for the cell reaction.
a) 0.63 V
b) 0.49 V
c) 1.23 V
d) 3.24 V
Answer: B
Explanation
Given,
equilibrium constant Kc = 4 × 1016
E° (cell) = 0.059/2 log10 Kc
E°(cell) = 0.059/2 log10 (4 × 1016)
=0.49V.
Video Explanation
- For the measurement of standard electrode potential, Zn is dipped in
a) 1 M ZnO solution
b) 1 M ZnSO4 solution
c) 1.5 M ZnSO4 solution
d) 0.1 M ZnSO4 solution
Answer: B
Video Explanation
- Zn(s)/Zn+2(aq) 1M | | Cu+2(aq) 1M/Cu(s) is representation of reaction in
a) Daniel cell
b) Downs cell
c) Voltaic cell
d) Nelsons cell
Answer: C
Video Explanation
- The electric charge for electrode decomposition of one gram equivalent of substance is
a) One Ampere per second
b) 96500 Coulombs per second
c) One Ampere for one hour
d) Charge on one mole of electrons
Answer D
Explanation
- Charge on one mole of electrons is equal to one Faraday, so one gram equivalent of a substance will be deposited by one mole of electrons.
- 1 g equivalent of a substance means one equivalent of substance which have total charge of one mole of electron.
Video Explanation
- The standard oxidation potential of Ni/Ni2+ electrode is 0.3 V. If this is combined with a hydrogen electrode in acid solution, at what pH of the solution with the measured e.m.f. be zero at 25°C? (Assume [Ni2+] = 1M)
a) 5.08
b) 4
c) 4.5
d) 5.25
Answer: A
Explanation
Given,
Standard oxidation potential of Ni/Ni2+ electrode, E°OP = 0.3 V,
Ni → Ni2+ + 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) + 0.059/2 log10([H+]2 / [Ni]+2)
0 = 0.3 + 0.059/2 log10([H+]2)
-log ([H+]) = 5.08
pH = 5.08.
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