A solution of copper sulphate electrolysed for 20 minute with a current of 1 . 5 Ampere. Calculate the mass of copper deposited at the cathode. F = 96500 C

From Faraday's First law of electrolysis, mass of material deposited when electricity is passed is given by W = ZIt - - - - - > 1 Where, W = Mass of material deposited Z = Electrochemical equivalent of the substance., i.e., Z = Equivalent mass Faraday ' s constant The equilvalent mass of a substance is the quantity of material deposited or dissolved by 1 F = 96500 C of electricity. Cu 2 + + 2 e - → Cu Z = Equivalent mass Faraday ' s constant = atomic mass of copper 2 96500 = 63 . 5 2 96500 I = Strength of current in amperes = 1 . 5 A t = time = 20 min = 1200 sec Substitute the above values in equation in 1 W = 63 . 5 2 96500 × 1 . 5 × 1200 W = 63 . 5 × 1 . 5 × 1200 2 × 96500 = 114300 193000 = 0 . 592 g Therefore, mass of copper deposited at cathode = 0 . 592 g

Fuel Cells are better than other cells. Give any two reasons.

The two reasons for fuel cells are better than other cells are, 1. Fuel cells are more efficient. Efficiency of fuel cell is about 70 % . It converts energy of a fuel directly into electricity. Therefore, more efficient than the conventional method. 2. Fuel cells do not cause pollution. For example, in a hydrogen-oxygen fuel cell the only product produce is water. In spacecrafts, this water is used for meeting the requirements of the astronauts.

If the value of molar conductivities at infinite dilution for CH 3 COOH , HCl and NaCl are 390 . 5 , 425 . 4 and 126 . 4 S cm 2 mol - 1 respectively at 298 K . Calculate the molar conductivity at infinite dilution of CH 3 COONa .

Given: The molar conductivity of Λ ∞ m CH 3 COOH = 390 . 5 S cm 2 mol - 1 The molar conductivity of Λ ∞ m HCl = 425 . 4 S cm 2 mol - 1 The molar conductivity of Λ ∞ m NaCl = 126 . 4 S cm 2 mol - 1 According to Kohlrausch's law Λ ∞ m CH 3 COONa = Λ ∞ m CH 3 COOH + Λ ∞ m NaCl - Λ ∞ m HCl = 390 . 5 + 126 . 4 - 425 . 4 = 91 . 5 S cm 2 mol - 1 The molar conductivity at infinite dilution of CH 3 COONa is 91 . 5 S cm 2 mol - 1 .

Write the chemical equation of reaction taking place on the anode in a cadmium-nickel storage cell.

Cadmium acts as an anode and the metallic plate filled with nickel oxide in the solution of potassium hydroxide acts as a cathode in the cadmium-nickel cell. In this cell water is used as an electrolyte. The oxidation process occurs at the anode. The reaction taking place on the anode in this cell is the following: Cd + OH - aq → Cd OH 2 s + 2 e -

The conductivity of 0 . 10 M solution of KCl at 298 K is 0 . 0129 S cm - 1 . Calculate its molar conductivity.

Given: The concentration of the solution = 0 . 10 M The conductivity of the solution k = 0 . 0129 S cm - 1 = 1 . 29 × 10 - 2 ohm - 1 cm - 1 Molar conductivity, ∧ m = k × 1000 M ohm - 1 cm 2 mol - 1 = 1 . 29 × 10 - 2 × 1000 0 . 10 ohm - 1 cm 2 mol - 1 = 129 ohm - 1 cm 2 mol - 1

Corrosion is an electrochemical phenomenon. Explain.

The process to form undesirable compounds usually oxide by reaction of the metal surface and air or water in the environment on the surface of the metal when it is exposed to air is called corrosion. It is an electrochemical phenomenon. According to the electrochemical theory of corrosion, the non-uniform surface of metal or impurities present in iron behave like a small electric cell in the presence of water containing dissolved oxygen or carbon dioxide. In this small electrolytic cell, pure iron acts as an anode while impure portions act as a cathode. Overall cell reaction- Fe s + 4 H + + O 2 → 2 Fe aq 2 + + 2 H 2 O The ferrous ion is oxidised by the dissolved oxygen or atmospheric oxygen to ferric oxides which form a hydrated ferric oxide on hydration. 4 Fe 2 + aq + O 2 g + 4 H + → 2 Fe 2 O 3 + 8 H + Fe 2 O 3 + xH 2 O → Fe 2 O 3 . x H 2 O Rust

Write any two factors which affects the conductance of electrolysis.

The factors affecting the conductance of an electrolyte are the following: (i) Concentration of ions- The ions are the charge carrier in electrolytes. So, the conductance of electrolytes increases with the increase in the concentration of ions. (ii) Nature of electrolytes- The conductance of electrolytes depends on the ions. Strong electrolytes completely dissociate into the solution, so they produce more ions. Therefore, the conductance of strong electrolytes is more than weak electrolytes.

State Faraday's first law of electrolysis.

Faradays first electrolysis Law states that the quantity of reaction taking place in terms of mass of ions formed or discharged from an electrolyte is proportional to the amount of electric current passed. Since, electric current (ampere) is the number of coulombs ( Q ) flowing in one second, Mass of the ions formed or reacted ( m ) α electric current α Q , or m ∝ Q or m = ZQ . Where, Z is a proportionality constant, called the chemical equivalent of the element.

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Draw a labelled diagram of 'Standard Hydrogen Electrode'.

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