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Q2.18 (iii):
Predict the products of electrolysis in each of the following:
(iii) A dilute solution of (H_{2}SO_{4}) with platinum electrodes.
Solution :
Given Variables & Initial Setup
The system consists of a dilute aqueous solution of sulfuric acid ($H_{2}SO_{4}$) undergoing electrolysis using inert platinum (Pt) electrodes. The ionic species present in the electrolyte are:
- From the dissociation of water: $H_{2}O(l) \rightleftharpoons H^{+}(aq) + OH^{-}(aq)$
- From the dissociation of sulfuric acid: $H_{2}SO_{4}(aq) \rightarrow 2H^{+}(aq) + SO_{4}^{2-}(aq)$
The total concentration of $H^{+}$ ions is significantly high due to the presence of both the acid and water dissociation equilibrium. The potential competitors for oxidation at the anode and reduction at the cathode are identified as follows:
Step 1: Identifying Cathode Reactions (Reduction)
At the cathode, the cations present are $H^{+}$. Since there is only one type of cation, the reduction reaction is straightforward:
$H^{+}(aq) + e^{-} \rightarrow \frac{1}{2}H_{2}(g)$
[Per the principle of competitive discharge, $H^{+}$ is the only species competing for reduction at the cathode in this acidic medium.]
Step 2: Identifying Anode Reactions (Oxidation)
At the anode, the competing anions are $OH^{-}$ and $SO_{4}^{2-}$. However, we must also consider the oxidation of water molecules. The standard electrode potentials ($E^{\circ}$) are as follows:
| Reaction | $E^{\circ}$ (V) |
|---|---|
| $2H_{2}O(l) \rightarrow O_{2}(g) + 4H^{+}(aq) + 4e^{-}$ | $+1.23\text{ V}$ |
| $2SO_{4}^{2-}(aq) \rightarrow S_{2}O_{8}^{2-}(aq) + 2e^{-}$ | $+1.96\text{ V}$ |
[By comparing the standard oxidation potentials, the reaction with the lower positive potential (for oxidation) occurs preferentially.]
Since the oxidation potential of water ($1.23\text{ V}$) is significantly lower than that of the sulfate ion ($1.96\text{ V}$), water molecules are oxidized at the anode instead of the sulfate ions.
Step 3: Visual Representation of the Electrolytic Cell
Step 4: Summary of Cell Reactions
Combining the reactions at both electrodes:
- Cathode: $4H^{+}(aq) + 4e^{-} \rightarrow 2H_{2}(g)$
- Anode: $2H_{2}O(l) \rightarrow O_{2}(g) + 4H^{+}(aq) + 4e^{-}$
- Net Reaction: $2H_{2}O(l) \rightarrow 2H_{2}(g) + O_{2}(g)$
[This confirms that the electrolysis of dilute $H_{2}SO_{4}$ is essentially the electrolysis of water, as the $H^{+}$ and $SO_{4}^{2-}$ ions act as charge carriers but are not consumed in the net redox process.]
Final Solution: The product at the cathode is Hydrogen gas ($H_{2}$) and the product at the anode is Oxygen gas ($O_{2}$).
More Questions from Class 12 Chemistry Electrochemistry Exercises
- Q2.1: Arrange the following metals in the order in which they displace each other from the solution of their salts. Al, Cu, Fe, Mg and Zn.
- Q2.1: Arrange the following metals in the order in which they displace each other from the solution of their salts. Al, Cu, Fe, Mg and Zn.
- Q2.10: The conductivity of sodium chloride at 298 K has been determined at different concentrations and the results are given below: Calculate (\Lambda_{m}) for all concentrations and draw a plot between (\Lambda_{m}) and (c^{1/2}). Find the value of (\Lambda^{0}_{m}).
- Q2.10: The conductivity of sodium chloride at 298 K has been determined at different concentrations and the results are given below: Calculate \(\Lambda_{m}\) for all concentrations and draw a plot between \(\Lambda_{m}\) and \(c^{1/2}\). Find the value of \(\Lambda_{m}^{\circ}\).
- Q2.11: Conductivity of 0.00241 M acetic acid is 7.896 (\times) (10^{-5}) S (cm^{-1}). Calculate its molar conductivity. If (\Lambda^{0}_{m}) for acetic acid is 390.5 S (cm^{2} mol^{-1}), what is its dissociation constant?
- Q2.11: Conductivity of 0.00241 M acetic acid is \(7.896 \times 10^{-5} S cm^{-1}\). Calculate its molar conductivity. If \(\Lambda_{m}^{\circ}\) for acetic acid is \(390.5 S cm^{2} mol^{-1}\), what is its dissociation constant?
- Q2.12 (i): How much charge is required for the following reduction: (i) 1 mol of (Al^{3+}) to Al?
- Q2.12 (ii): How much charge is required for the following reduction: (ii) 1 mol of (Cu^{2+}) to Cu?
- Q2.12 (iii): How much charge is required for the following reduction: (iii) 1 mol of (MnO_{4}^{-}) to (Mn^{2+})?
- Q2.12(i): How much charge is required for the following reduction: 1 mol of \(Al^{3+}\) to Al?
- Q2.12(ii): How much charge is required for the following reduction: 1 mol of \(Cu^{2+}\) to Cu?
- Q2.12(iii): How much charge is required for the following reduction: 1 mol of \(MnO_{4}^{-}\) to \(Mn^{2+}\)?
- Q2.13 (i): How much electricity in terms of Faraday is required to produce (i) 20.0 g of Ca from molten (CaCl_{2})?
- Q2.13 (ii): How much electricity in terms of Faraday is required to produce (ii) 40.0 g of Al from molten (Al_{2}O_{3})?
- Q2.13(i): How much electricity in terms of Faraday is required to produce 20.0 g of Ca from molten \(CaCl_{2}\)?
- Q2.13(ii): How much electricity in terms of Faraday is required to produce 40.0 g of Al from molten \(Al_{2}O_{3}\)?
- Q2.14 (i): How much electricity is required in coulomb for the oxidation of (i) 1 mol of (H_{2}O) to (O_{2})?
- Q2.14 (ii): How much electricity is required in coulomb for the oxidation of (ii) 1 mol of (FeO) to (Fe_{2}O_{3})?
- Q2.14(i): How much electricity is required in coulomb for the oxidation of 1 mol of \(H_{2}O\) to \(O_{2}\)?
- Q2.14(ii): How much electricity is required in coulomb for the oxidation of 1 mol of FeO to \(Fe_{2}O_{3}\)?
- Q2.15: A solution of (Ni(NO_{3})_{2}) is electrolysed between platinum electrodes using a current of 5 amperes for 20 minutes. What mass of Ni is deposited at the cathode?
- Q2.15: A solution of \(Ni(NO_{3})_{2}\) is electrolysed between platinum electrodes using a current of 5 amperes for 20 minutes. What mass of Ni is deposited at the cathode?
- Q2.16: Three electrolytic cells A,B,C containing solutions of (ZnSO_{4}), (AgNO_{3}) and (CuSO_{4}), respectively are connected in series. A steady current of 1.5 amperes was passed through them until 1.45 g of silver deposited at the cathode of cell B. How long did the current flow? What mass of copper and zinc were deposited?
- Q2.16: Three electrolytic cells A,B,C containing solutions of \(ZnSO_{4}\), \(AgNO_{3}\) and \(CuSO_{4}\), respectively are connected in series. A steady current of 1.5 amperes was passed through them until 1.45 g of silver deposited at the cathode of cell B. How long did the current flow? What mass of copper and zinc were deposited?
- Q2.17 (i): Using the standard electrode potentials, predict if the reaction between the following is feasible: (i) (Fe^{3+}(aq)) and (I^{-}(aq))
- Q2.17 (ii): Using the standard electrode potentials, predict if the reaction between the following is feasible: (ii) (Ag^{+} (aq)) and Cu(s)
- Q2.17 (iii): Using the standard electrode potentials, predict if the reaction between the following is feasible: (iii) (Fe^{3+} (aq)) and (Br^{-} (aq))
- Q2.17 (iv): Using the standard electrode potentials, predict if the reaction between the following is feasible: (iv) Ag(s) and (Fe^{3+} (aq))
- Q2.17 (v): Using the standard electrode potentials, predict if the reaction between the following is feasible: (v) (Br_{2} (aq)) and (Fe^{2+} (aq)).
- Q2.17(i): Using the standard electrode potentials given in Table 3.1, predict if the reaction between the following is feasible: \(Fe^{3+}(aq)\) and \(I^{-}(aq)\)
- Q2.17(ii): Using the standard electrode potentials given in Table 3.1, predict if the reaction between the following is feasible: \(Ag^{+} (aq)\) and \(Cu(s)\)
- Q2.17(iii): Using the standard electrode potentials given in Table 3.1, predict if the reaction between the following is feasible: \(Fe^{3+} (aq)\) and \(Br^{-} (aq)\)
- Q2.17(iv): Using the standard electrode potentials given in Table 3.1, predict if the reaction between the following is feasible: \(Ag(s)\) and \(Fe^{3+} (aq)\)
- Q2.17(v): Using the standard electrode potentials given in Table 3.1, predict if the reaction between the following is feasible: \(Br_{2} (aq)\) and \(Fe^{2+} (aq)\).
- Q2.18 (i): Predict the products of electrolysis in each of the following: (i) An aqueous solution of (AgNO_{3}) with silver electrodes.
- Q2.18 (ii): Predict the products of electrolysis in each of the following: (ii) An aqueous solution of (AgNO_{3}) with platinum electrodes.
- Q2.18 (iv): Predict the products of electrolysis in each of the following: (iv) An aqueous solution of (CuCl_{2}) with platinum electrodes.
- Q2.18(i): Predict the products of electrolysis in each of the following: An aqueous solution of \(AgNO_{3}\) with silver electrodes.
- Q2.18(ii): Predict the products of electrolysis in each of the following: An aqueous solution of \(AgNO_{3}\) with platinum electrodes.
- Q2.18(iii): Predict the products of electrolysis in each of the following: A dilute solution of \(H_{2}SO_{4}\) with platinum electrodes.
- Q2.18(iv): Predict the products of electrolysis in each of the following: An aqueous solution of \(CuCl_{2}\) with platinum electrodes.
- Q2.2: Given the standard electrode potentials, (K^{+}/K) = –2.93V, (Ag^{+}/Ag) = 0.80V, (Hg^{2+}/Hg) = 0.79V (Mg^{2+}/Mg) = –2.37 V, (Cr^{3+}/Cr) = – 0.74V Arrange these metals in their increasing order of reducing power.
- Q2.2: Given the standard electrode potentials, \(K^{+}/K = –2.93V\), \(Ag^{+}/Ag = 0.80V\), \(Hg^{2+}/Hg = 0.79V\) \(Mg^{2+}/Mg = –2.37 V\), \(Cr^{3+}/Cr = – 0.74V\) Arrange these metals in their increasing order of reducing power.
- Q2.3 (i): Depict the galvanic cell in which the reaction (Zn(s)+2Ag^{+}(aq) \rightarrow Zn^{2+}(aq)+2Ag(s)) takes place. Further show: (i) Which of the electrode is negatively charged?
- Q2.3 (ii): Depict the galvanic cell in which the reaction (Zn(s)+2Ag^{+}(aq) \rightarrow Zn^{2+}(aq)+2Ag(s)) takes place. Further show: (ii) The carriers of the current in the cell.
- Q2.3 (iii): Depict the galvanic cell in which the reaction (Zn(s)+2Ag^{+}(aq) \rightarrow Zn^{2+}(aq)+2Ag(s)) takes place. Further show: (iii) Individual reaction at each electrode.
- Q2.3(i): Depict the galvanic cell in which the reaction \(Zn(s)+2Ag^{+}(aq) \rightarrow Zn^{2+}(aq)+2Ag(s)\) takes place. Further show: Which of the electrode is negatively charged?
- Q2.3(ii): Depict the galvanic cell in which the reaction \(Zn(s)+2Ag^{+}(aq) \rightarrow Zn^{2+}(aq)+2Ag(s)\) takes place. Further show: The carriers of the current in the cell.
- Q2.3(iii): Depict the galvanic cell in which the reaction \(Zn(s)+2Ag^{+}(aq) \rightarrow Zn^{2+}(aq)+2Ag(s)\) takes place. Further show: Individual reaction at each electrode.
- Q2.4 (i): Calculate the standard cell potentials of galvanic cell in which the following reaction takes place: (i) (2Cr(s) + 3Cd^{2+}(aq) \rightarrow 2Cr^{3+}(aq) + 3Cd) Calculate the (\Delta_{r}G^{o}) and equilibrium constant of the reaction.
- Q2.4 (ii): Calculate the standard cell potentials of galvanic cell in which the following reaction takes place: (ii) (Fe^{2+}(aq) + Ag^{+}(aq) \rightarrow Fe^{3+}(aq) + Ag(s)) Calculate the (\Delta_{r}G^{o}) and equilibrium constant of the reaction.
- Q2.4(i): Calculate the standard cell potentials of galvanic cell in which the following reaction takes place: \(2Cr(s) + 3Cd^{2+}(aq) \rightarrow 2Cr^{3+}(aq) + 3Cd(s)\) Calculate the \(\Delta_{r}G^{\circ}\) and equilibrium constant of the reaction.
- Q2.4(ii): Calculate the standard cell potentials of galvanic cell in which the following reaction takes place: \(Fe^{2+}(aq) + Ag^{+}(aq) \rightarrow Fe^{3+}(aq) + Ag(s)\) Calculate the \(\Delta_{r}G^{\circ}\) and equilibrium constant of the reaction.
- Q2.5 (i): Write the Nernst equation and emf of the following cell at 298 K: (i) (Mg(s)|Mg^{2+}(0.001M)||Cu^{2+}(0.0001 M)|Cu(s))
- Q2.5 (ii): Write the Nernst equation and emf of the following cell at 298 K: (ii) (Fe(s)|Fe^{2+}(0.001M)||H^{+}(1M)|H_{2}(g)(1bar)| Pt(s))
- Q2.5 (iii): Write the Nernst equation and emf of the following cell at 298 K: (iii) (Sn(s)|Sn^{2+}(0.050 M)||H^{+}(0.020 M)|H_{2}(g) (1 bar)|Pt(s))
- Q2.5 (iv): Write the Nernst equation and emf of the following cell at 298 K: (iv) (Pt(s)|Br^{-}(0.010 M)|Br_{2}(l )||H^{+}(0.030 M)| H_{2}(g) (1 bar)|Pt(s)).
- Q2.5(i): Write the Nernst equation and emf of the following cell at 298 K: \(Mg(s)|Mg^{2+}(0.001M)||Cu^{2+}(0.0001 M)|Cu(s)\)
- Q2.5(ii): Write the Nernst equation and emf of the following cell at 298 K: \(Fe(s)|Fe^{2+}(0.001M)||H^{+}(1M)|H_{2}(g)(1bar)| Pt(s)\)
- Q2.5(iii): Write the Nernst equation and emf of the following cell at 298 K: \(Sn(s)|Sn^{2+}(0.050 M)||H^{+}(0.020 M)|H_{2}(g) (1 bar)|Pt(s)\)
- Q2.5(iv): Write the Nernst equation and emf of the following cell at 298 K: \(Pt(s)|Br^{-}(0.010 M)|Br_{2}(l )||H^{+}(0.030 M)| H_{2}(g) (1 bar)|Pt(s)\).
- Q2.6: In the button cells widely used in watches and other devices the following reaction takes place: (Zn(s) + Ag_{2}O(s) + H_{2}O(l ) \rightarrow Zn^{2+}(aq) + 2Ag(s) + 2OH^{-}(aq)) Determine (\Delta_{r}G^{o}) and (E^{o}) for the reaction.
- Q2.6: In the button cells widely used in watches and other devices the following reaction takes place: \(Zn(s) + Ag_{2}O(s) + H_{2}O(l ) \rightarrow Zn^{2+}(aq) + 2Ag(s) + 2OH^{-}(aq)\) Determine \(\Delta_{r}G^{\circ}\) and \(E^{\circ}\) for the reaction.
- Q2.7: Define conductivity and molar conductivity for the solution of an electrolyte. Discuss their variation with concentration.
- Q2.7: Define conductivity and molar conductivity for the solution of an electrolyte. Discuss their variation with concentration.
- Q2.8: The conductivity of 0.20 M solution of KCl at 298 K is 0.0248 S (cm^{-1}). Calculate its molar conductivity.
- Q2.8: The conductivity of 0.20 M solution of KCl at 298 K is \(0.0248 S cm^{-1}\). Calculate its molar conductivity.
- Q2.9: The resistance of a conductivity cell containing 0.001M KCl solution at 298 K is 1500 (\Omega). What is the cell constant if conductivity of 0.001M KCl solution at 298 K is 0.146 (\times) (10^{-3}) S (cm^{-1}).
- Q2.9: The resistance of a conductivity cell containing 0.001M KCl solution at 298 K is \(1500 \Omega\). What is the cell constant if conductivity of 0.001M KCl solution at 298 K is \(0.146 \times 10^{-3} S cm^{-1}\).
CBSE Solutions for Class 12 Chemistry Electrochemistry
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