Electrochemistry

At 25°C, the molar conductance of 0.007 M hydrofluoric acid is 150 mho cm²mol^-1 and its Λ°_m = 500 cm²mol^-1. The value of the dissociation constant of the acid at the given concentration at 25°C is

• 7 × 10^-4 M

• 7 × 10^-5 M

• 9 × 10^-3 M

• 9 × 10^-4 M

The standard reduction potential E^o for half-reaction are:

Zn $\to$ Zn²⁺ + 2e^- ; E° = + 0.76V

Fe $\to$ Fe²⁺ + 2e^- ; E° = + 0.41 V

The EMF of the cell reaction

Fe²⁺ + Zn $\to$ Zn²⁺ + Fe is :

• - 0.35 V

• + 0.35 V

• + 1.17 V

• - 1.17 V

The formal potential of Fe³⁺ /Fe²⁺ in a sulphuric acid and phosphoric acid mixture (E° = +0.61 V) is much lower than the standard potential (E° = +0.77 V). This is due to

• formation of the species [FeHPO₄]⁺

• lowering of potential upon complexation

• formation of the species [FesO₄]+

• high acidity of the medium

The potential of a hydrogen electrode at pH = 10 is 

• 0.59 V

• 0.00 V

• -0.59 V

• - 0.059 

A cell is represented by Zn|Zn²⁺ (aq) || Cu²⁺ (aq)| Cu. Given, Cu²⁺ + 2e^- → Zn, E° = -0.763 V. Write the cell reactions, emf of the cell and state whether the cell reaction will be spontaneous or not?

Cadmium rods are used for which purpese?

• Emit electrons

• Absorb neutrons

• Emit neutrons

• Absorb electrons

What is the effect of dilution on the equivalent conductance of strong electrolyte?

• Decrease on dilution

• Remains unchanged

• Increase on dilution

• None of the above

In Down's method for the extraction of sodium, the melting point of the electrolyte is lowered by adding

• potassium chloride

• calcium chloride

• both calcium chloride and potassium fluoride

• potassium fluoride only

 Calcium is obtained by

• electrolysis of molten CaCl₂

• electrolysis of solution of CaCl₂ in water

• reduction of CaCl₂ with carbon

• roasting of lime stone

A current of 12 ampere is passed through an electrolytic cell containing aqueous NiSO₄ solution. Both Ni and H₂ gas are formed at the cathode. The current efficiency is 60%. What is the mass of nickel deposited on the cathode per hour?

• 7.883g

• 3.941g

• 5.91g

• 2.645g