Question 1

Q1: 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 .

Accepted Answer

The ability of a metal to displace another metal from its salt solution depends on its position in the electrochemical series. A metal with a lower standard reduction potential (more negative) is more reactive and can displace a metal with a higher standard reduction potential (less negative or posi...

Question 2

Q10: The conductivity of sodium chloride at 298 K has been determined at different concentrations and the results are given below: Concentration/M 0.001 0....

Accepted Answer

Step 1: Data Tabulation and Unit Conversion We need to calculate molar conductivity ($ \Lambda_m $) and the square root of concentration ($c^{1/2}$). It is convenient to work with units of S cm$^2$ mol$^{-1}$ for $ \Lambda_m $ and (mol L$^{-1}$)$^{1/2}$ for $c^{1/2}$. First, convert conductivity $\k...

Question 3

Q11: Conductivity of 0.00241 M acetic acid is $7.896 	imes 10^{-5} 	ext{ S cm}^{-1}$. Calculate its molar conductivity. If $ \Lambda_m^\circ $ for acetic...

Accepted Answer

Given: Concentration of acetic acid, $c = 0.00241 	ext{ M}$ Conductivity, $ \kappa = 7.896 	imes 10^{-5} 	ext{ S cm}^{-1} $ Limiting molar conductivity, $ \Lambda_m^\circ = 390.5 	ext{ S cm}^2 	ext{mol}^{-1} $ Part 1: Calculate Molar Conductivity ($ \Lambda_m $) Formula: $$ \Lambda_m = \frac{10...

Question 4

Q12: How much charge is required for the following reductions: (i) 1 mol of $Al^{3+}$ to Al ? (ii) 1 mol of $Cu^{2+}$ to Cu ? (iii) 1 mol of $MnO_4^-$ to $...

Accepted Answer

The charge on one mole of electrons is equal to one Faraday ($F$), which is approximately $96500 	ext{ C mol}^{-1}$. We need to determine the number of moles of electrons required for each reduction. (i) 1 mol of $Al^{3+}$ to Al The reduction half-reaction is: $$ 	ext{Al}^{3+} + 3e^- ightarrow \...

Question 5

Q13: How much electricity in terms of Faraday is required to produce (i) 20.0 g of Ca from molten $CaCl_2$ ? (ii) 40.0 g of Al from molten $Al_2O_3$ ?

Accepted Answer

(i) 20.0 g of Ca from molten $CaCl_2$ Step 1: Write the electrode reaction. Calcium is produced by the reduction of $ 	ext{Ca}^{2+} $ ions at the cathode. $$ 	ext{Ca}^{2+} + 2e^- ightarrow 	ext{Ca(s)} $$ This equation shows that 1 mole of Ca (atomic mass = 40.0 g/mol) is produced by 2 moles of...

Question 6

Q14: How much electricity is required in coulomb for the oxidation of (i) 1 mol of $H_2O$ to $O_2$ ? (ii) 1 mol of FeO to $Fe_2O_3$ ?

Accepted Answer

(i) 1 mol of $H_2O$ to $O_2$ Step 1: Write the balanced oxidation half-reaction. The oxidation of water produces oxygen gas. $$ 2	ext{H}_2	ext{O(l)} ightarrow 	ext{O}_2	ext{(g)} + 4	ext{H}^+	ext{(aq)} + 4e^- $$ Step 2: Determine electrons transferred per mole of reactant. The balanced equati...

Question 7

Q15: 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 th...

Accepted Answer

Given: Current, $I = 5 	ext{ A}$ Time, $t = 20 	ext{ minutes} = 20 	imes 60 	ext{ seconds} = 1200 	ext{ s}$ Electrolyte: $ 	ext{Ni(NO}_3)_2 $, which provides $ 	ext{Ni}^{2+} $ ions. Molar mass of Ni, $M = 58.7 	ext{ g/mol}$ To Find: Mass of Ni deposited, $w$ Step 1: Calculate the total charg...

Question 8

Q16: 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...

Accepted Answer

Given: Current, $I = 1.5 	ext{ A}$ Mass of silver deposited in cell B, $w_{	ext{Ag}} = 1.45 	ext{ g}$ Molar mass of Ag, $M_{	ext{Ag}} = 108 	ext{ g/mol}$ Molar mass of Zn, $M_{	ext{Zn}} = 65.4 	ext{ g/mol}$ Molar mass of Cu, $M_{	ext{Cu}} = 63.5 	ext{ g/mol}$ Part 1: How long did the curren...

Question 9

Q17: Using the standard electrode potentials given in Table 3.1, predict if the reaction between the following is feasible: (i) $Fe^{3+}(aq)$ and $I^-(aq)$...

Accepted Answer

A redox reaction is feasible (spontaneous) if the standard cell potential ($E^\circ_{	ext{cell}}$) for the reaction is positive. $E^\circ_{	ext{cell}} = E^\circ_{	ext{cathode}} - E^\circ_{	ext{anode}}$. (i) $Fe^{3+}(aq)$ and $I^-(aq)$ Possible reduction: $ 	ext{Fe}^{3+}	ext{(aq)} + e^- ighta...

Question 10

Q18: Predict the products of electrolysis in each of the following: (i) An aqueous solution of $AgNO_3$ with silver electrodes. (ii) An aqueous solution of...

Accepted Answer

The products of electrolysis depend on the nature of the electrolyte and the electrodes used. (i) An aqueous solution of $AgNO_3$ with silver electrodes (reactive electrodes). Electrolyte contains: $ 	ext{Ag}^+	ext{(aq)}, 	ext{NO}_3^-	ext{(aq)}, 	ext{H}_2	ext{O} $ At Cathode (Reduction): Possi...

Question 11

Q2: Given the standard electrode potentials, $K^+/K = -2.93V, Ag^+/Ag = 0.80V$, $Hg^{2+}/Hg = 0.79V$ $Mg^{2+}/Mg = -2.37V, Cr^{3+}/Cr = -0.74V$ Arrange th...

Accepted Answer

The reducing power of a metal is its tendency to lose electrons, i.e., to get oxidized. A metal with a lower (more negative) standard reduction potential ($E^\circ$) has a greater tendency to get oxidized and is therefore a stronger reducing agent. The standard electrode potentials ($E^\circ$) of th...

Question 12

Q3: 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 electr...

Accepted Answer

The galvanic cell for the given reaction is depicted as follows: Cell Representation: $$ 	ext{Zn(s)} | 	ext{Zn}^{2+}	ext{(aq)} || 	ext{Ag}^{+}	ext{(aq)} | 	ext{Ag(s)} $$ A zinc electrode is dipped in a solution of zinc sulphate, and a silver electrode is dipped in a solution of silver nitrate....

Question 13

Q4: Calculate the standard cell potentials of galvanic cell in which the following reactions take place: (i) $2Cr(s) + 3Cd^{2+}(aq) \rightarrow 2Cr^{3+}(a...

Accepted Answer

(i) $2	ext{Cr(s)} + 3	ext{Cd}^{2+}	ext{(aq)} ightarrow 2	ext{Cr}^{3+}	ext{(aq)} + 3	ext{Cd(s)}$ Half-reactions: Anode (Oxidation): $ 	ext{Cr(s)} ightarrow 	ext{Cr}^{3+}	ext{(aq)} + 3e^- $ Cathode (Reduction): $ 	ext{Cd}^{2+}	ext{(aq)} + 2e^- ightarrow 	ext{Cd(s)} $ Given Standard P...

Question 14

Q5: Write the Nernst equation and emf of the following cells at 298 K : (i) $Mg(s)|Mg^{2+}(0.001 M) || Cu^{2+}(0.0001 M)|Cu(s)$ (ii) $Fe(s)|Fe^{2+}(0.001...

Accepted Answer

The Nernst equation for a cell at 298 K is: $E_{	ext{cell}} = E^\circ_{	ext{cell}} - \frac{0.0591}{n} \log Q$ (i) $Mg(s)|Mg^{2+}(0.001 M) || Cu^{2+}(0.0001 M)|Cu(s)$ Cell Reaction: $ 	ext{Mg(s)} + 	ext{Cu}^{2+}	ext{(aq)} ightarrow 	ext{Mg}^{2+}	ext{(aq)} + 	ext{Cu(s)} $ Here, $n=2$. $E^\ci...

Question 15

Q6: In the button cells widely used in watches and other devices the following reaction takes place: $Zn(s) + Ag_2O(s) + H_2O(l) \rightarrow Zn^{2+}(aq) +...

Accepted Answer

The overall reaction can be split into two half-reactions: Anode (Oxidation): $ 	ext{Zn(s)} ightarrow 	ext{Zn}^{2+}	ext{(aq)} + 2e^- $; $E^\circ_{	ext{Zn}^{2+}/	ext{Zn}} = -0.76 	ext{ V}$ Cathode (Reduction): $ 	ext{Ag}_2	ext{O(s)} + 	ext{H}_2	ext{O(l)} + 2e^- ightarrow 2	ext{Ag(s)} +...

Question 16

Q7: Define conductivity and molar conductivity for the solution of an electrolyte. Discuss their variation with concentration.

Accepted Answer

Conductivity ($ \kappa $): Conductivity of a solution is defined as the conductance of a solution of 1 cm length with an area of cross-section of 1 cm$^2$. It is the inverse of resistivity ($ ho $).  $$ \kappa = \frac{1}{ho} = \frac{1}{R} \frac{l}{A} $$ Its SI unit is Siemens per meter ($ 	ext{...

Question 17

Q8: The conductivity of 0.20 M solution of KCl at 298 K is $0.0248 	ext{ S cm}^{-1}$. Calculate its molar conductivity.

Accepted Answer

Given: Concentration of KCl solution, $c = 0.20 	ext{ M} = 0.20 	ext{ mol L}^{-1}$ Conductivity, $ \kappa = 0.0248 	ext{ S cm}^{-1} $ To Find: Molar conductivity, $ \Lambda_m $ Formula: The molar conductivity ($ \Lambda_m $) is related to conductivity ($ \kappa $) and molar concentration ($c$) by...

Question 18

Q9: The resistance of a conductivity cell containing 0.001 M KCl solution at 298 K is $1500 \Omega$. What is the cell constant if conductivity of 0.001 M...

Accepted Answer

Given: Concentration of KCl solution, $c = 0.001 	ext{ M}$ Resistance of the solution, $R = 1500 \Omega$ Conductivity of the solution, $ \kappa = 0.146 	imes 10^{-3} 	ext{ S cm}^{-1} $ To Find: The cell constant, $G^$ Formula: The relationship between conductivity ($ \kappa $), resistance ($R$),...

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