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Practice each question, then open the answer or worked solution.
A galvanic cell has an electrical potential of 1.1V. If an opposing potential of 1.1V is applied to this cell, what will happen to the cell reaction and current flowing through the cell?
The cell reaction stops and there will be no flow of current through the cell when the opposing potential becomes equal to electrical potential. Therefore no chemical reaction takes place.
How will the pH of brine (aq. NaCl solution) be affected when it is electrolyzed?
NaCl (aq)→Na+ (aq) + Cl– (aq)
Cathode: H2O(l ) + e–→ 1/2 H2(g) + OH– (aq)
Anode: Cl– (aq) → 1/2 Cl2(g) + e–
Overall reaction: NaCl(aq)+H2O(l)→NaOH(aq)+H2(g)+Cl2(g)
NaOH is a strong base, they turn the brine solution basic and pH will increase.
Unlike dry cell, the mercury cell has a constant cell potential throughout its useful life. Why?
The electrolyte is not consumed in the cell and thus the current will deliver at constant potential throughout,
overall reaction contains no ions whose concentration can change over time. So, the cell potential remains constant throughout the mercury cell life.
Solutions of two electrolytes ‘A’ and ‘B are diluted. The of ‘B’ increases 1.5 times while that of A increases 25 times. Which of the two is a strong electrolyte? Justify your answer.
Electrolyte B is strong as on dilution the number of ions remains the same, only interionic attraction decreases; therefore, the increase in Λm is small.
When acidulated water (dil.H2SO4 solution) is electrolysed, will the pH of the solution be affected? Justify your answer.
Anode: 2H2O(l)→ O2(g) + 4H+ (aq) + 4e–
Cathode: 4H+ + 4e-→ 2H2
Overall cell reaction: 2H2O(l) → O2(g) + 2H2(g)
pH remains the same because concentration of H+ ions remains constant.
In an aqueous solution, how does specific conductivity of electrolytes change with the addition of water?
The addition of water dilutes the electrolyte. The number of ions in a given volume decreases and conductivity also reduces.
Which reference electrode is used to measure the electrode potential of other electrodes?
Standard hydrogen electrode (SHE) is used as a reference electrode. The potential of SHE is assigned the value zero. The electrode potential of other electrodes is measured with respect to this.
Consider a cell given below
Cu|Cu2+|| Cl—|Cl2, Pt
Write the reactions that occur at anode and cathode.
Galvanic cell: Cu|Cu2+|| Cl—|Cl2, Pt
Anode- Oxidation half-cell: Cu(s) → Cu2+ + 2e-
Cathode- Reduction half-cell: Cl2(g)+ 2e-→ 2Cl-
Thus, Cu is anode as it is getting oxidised.
Write the Nernst equation for the cell reaction in the Daniel cell. How will the ECell be affected when the concentration of Zn2+ ions is increased?
Ecell = E°cell – RT[Zn2+]/ nF[Cu2+]
Galvanic cell reaction: Zn(s)|Zn2+(aq)||Cu2+(aq)|Cu(s)
Anode- oxidation half-cell: Zn(s) → Zn2+ (aq)+ 2e
Cathode- reduction half-cell: Cu2+ (aq)+ 2e-→ Cu(s)
Overall reaction: Zn(s) + Cu2+ (aq) → Zn2+(aq) +Cu(s)
Ecell = E°cell – 0.059/2[Zn2+]/[Cu2+]
What advantage do the fuel cells have over primary and secondary batteries?
Fuel cells are cells that convert the energy of combustion of fuels like hydrogen, methanol into electrical energy. Fuel cells run continuously as long as reactants are supplied. Primary batteries discharge and are one-time use only, and secondary batteries can be recharged, but recharging takes a lot of time.