NEET Electrochemistry — Set 1

Question 1

A current of 0.5 A is passed through a CuSO$_4$ solution for 9650 s, and then the same current is passed through an AlCl$_3$ solution for 6433.33 s. What is the total mass of metal deposited? (Atomic masses: Cu = 63.5 g/mol, Al = 27 g/mol, F = 96500 C/mol)

Accepted Answer

Charge = $ 0.5 \times 9650 = 4825 \, C $. Cu: $ Cu^{2+} + 2e^- \rightarrow Cu $, Mass = $ \frac{4825}{96500} \times \frac{63.5}{2} = 0.05 \times 31.75 = 1.5875 \, g $. Charge = $ 0.5 \times 6433.33 = 3216.665 \, C $. Al: $ Al^{3+} + 3e^- \rightarrow Al $, Mass = $ \frac{3216.665}{96500} \times \frac{27}{3} = 0.03333 \times 9 = 0.3 \, g $. Total mass = $ 1.5875 + 0.3 = 1.8875 \, g $.

Question 2

The limiting molar conductivity of CaCl$_2$ is 258 S cm$^2$ mol$^{-1}$. If $ \lambda^\circ_{Ca^{2+}} = 119 \, S \, cm^2 \, mol^{-1} $, what is $ \lambda^\circ_{Cl^-} $?

Accepted Answer

$ \Lambda_m^\circ = \lambda^\circ_{Ca^{2+}} + 2\lambda^\circ_{Cl^-} $. $ 258 = 119 + 2\lambda^\circ_{Cl^-} $, $ 2\lambda^\circ_{Cl^-} = 139 $, $ \lambda^\circ_{Cl^-} = 69.5 \, S \, cm^2 \, mol^{-1} $.

Question 3

What is the time (in seconds) required to deposit 0.405 g of calcium from molten CaCl$_2$ using a current of 1.5 A? (Atomic mass of Ca = 40.5 g/mol, F = 96500 C/mol)

Accepted Answer

$ Ca^{2+} + 2e^- \rightarrow Ca $. 1 mol Ca (40.5 g) requires 2F. Moles = $ \frac{0.405}{40.5} = 0.01 \, mol $, Charge = $ 0.01 \times 2 \times 96500 = 1930 \, C $. $ t = \frac{Q}{I} = \frac{1930}{1.5} = 1286.67 \, s $.

NEET Chemistry: Electrochemistry — Practice Set 1

Q1. A current of 0.5 A is passed through a CuSO\(_4\) solution for 9650 s, and then the same current is passed through an AlCl\(_3\) solution for 6433.33 s. What is the total mass of metal deposited? (Atomic masses: Cu = 63.5 g/mol, Al = 27 g/mol, F = 96500 C/mol)

Q2. The limiting molar conductivity of CaCl\(_2\) is 258 S cm\(^2\) mol\(^{-1}\). If \( \lambda^\circ_{Ca^{2+}} = 119 \, S \, cm^2 \, mol^{-1} \), what is \( \lambda^\circ_{Cl^-} \)?

Q3. What is the time (in seconds) required to deposit 0.405 g of calcium from molten CaCl\(_2\) using a current of 1.5 A? (Atomic mass of Ca = 40.5 g/mol, F = 96500 C/mol)

Q4. The molar conductivity of LiCl at infinite dilution is 115.0 S cm\(^2\) mol\(^{-1}\). If \( \lambda^\circ_{Li^+} = 38.7 \, S \, cm^2 \, mol^{-1} \), what is \( \lambda^\circ_{Cl^-} \)?

Q5. A cell \( Zn(s) | Zn^{2+}(0.001 \, M) || Br_2(l) | Br^-(0.002 \, M) | Pt(s) \) operates at 298 K. What is the cell potential? (Given: \( E^\circ_{Zn^{2+}/Zn} = -0.76 \, V \), \( E^\circ_{Br_2/Br^-} = 1.07 \, V \))

Q6. The emf of a cell \( Ni(s) | Ni^{2+}(0.001 \, M) || Ag^+(0.002 \, M) | Ag(s) \) at 298 K is (Given: \( E^\circ_{Ni^{2+}/Ni} = -0.25 \, V \), \( E^\circ_{Ag^+/Ag} = 0.80 \, V \))?

Q7. What is the emf of a cell with the reaction \( Mg(s) + 2Ag^+(aq) \rightarrow Mg^{2+}(aq) + 2Ag(s) \) at standard conditions, given \( E^\circ_{Mg^{2+}/Mg} = -2.36 \, V \) and \( E^\circ_{Ag^+/Ag} = 0.80 \, V \)?

Q8. The conductivity of a 0.025 M NaNO\(_3\) solution is 0.003 S cm\(^{-1}\), and its molar conductivity is 120 S cm\(^2\) mol\(^{-1}\). What is the degree of dissociation if \( \Lambda_m^\circ = 126.5 \, S \, cm^2 \, mol^{-1} \)?

Q9. The conductivity of a 0.01 M solution is 0.00141 S cm\(^{-1}\). What is its molar conductivity?

Q10. A current of 1 A deposits 0.635 g of Cu from CuSO\(_4\) in 1930 s. What is the time required to deposit 0.54 g of Al from Al\(_2\)(SO\(_4\))\(_3\) with the same current? (Atomic masses: Cu = 63.5 g/mol, Al = 27 g/mol, F = 96500 C/mol)