What are primary cells? Describe dry cell in short.

A dry cell consists of a metal container in which a low moisture electrolyte paste covers the graphite rod or a metal electrode. Generally, the metal container will be zinc whose base acts as a negative electrode (anode) and a carbon road acts as a positive electrode (cathode). It is surrounded by manganese dioxide and low moisture electrolyte like ammonium chloride paste, which will produce a maximum of 1.5V of voltage, and they are not reversible.

Find out the EMF of Zn / Zn + 2 ( 1 M ) / / Co 2 + ( 1 M ) / Co cell. For this cell E ° for Zn + 2 / Zn and Co + 2 / Co values are - 0 . 76 volt and + 0 . 28 volt respectively and their concentrations are 1 molar.

Given, The cell is Zn / Zn + 2 ( 1 M ) / / Co 2 + ( 1 M ) / Co . The cell reaction is Zn + Co 2 + ⇌ Zn 2 + + Co . The standard reduction potential of zinc is - 0 . 76 V and cobalt is + 0 . 28 V . Therefore, E Cell ° = + 0 . 28 - - 0 . 76 = 1 . 04 V . The EMF of the cell can be calculated as, E Cell = E Cell ° - 0 . 0591 n log product reactant . E Cell = 1 . 04 - 0 . 0591 2 log 1 M 1 M . E Cell = 1 . 04 - 0 . 0591 2 log 1 = 1 . 04 - 0 = 1 . 04 V . The EMF of the cell is 1 . 04 V .

Write Hess's law of constant heat summation.

Hess's Law of Constant Heat Summation (or just Hess's Law) states that regardless of the multiple stages or steps of a reaction, the total enthalpy change for the reaction is the sum of all changes. This law is a manifestation that enthalpy is a state function.

Write short notes on the following: Nernst equation.

The Nernst equation provides a relation between the cell potential of an electrochemical cell, the standard cell potential, temperature, and the reaction quotient. Even under non-standard conditions, the cell potentials of electrochemical cells can be determined with the help of the Nernst equation. E Cell = E Cell ° - 2 . 303 × R × T n × F log product reactant . Where, The gas constant is R . The temperature is T . The faraday is F .

Write a short note on secondary batteries.

These are batteries that can be recharged after use by passing current through the electrodes in the opposite direction, i.e. from the negative terminal to the positive terminal. For example, a lead storage battery that is used in automobiles and inverters can be recharged a limited number of times. The lead storage battery consists of a lead anode and the cathode is a lead grid packed with lead dioxide. Sulphuric acid with a concentration of 38 % is used as an electrolyte. The oxidation and reduction reactions involved in this process are listed below.

The standard molar conductivity Λ m ° for NaCl , HCl and CH 3 COONa are 126 . 4 S cm 2 mol - 1 , 425 . 9 S cm 2 mol - 1 and 91 . 0 S cm 2 mol - 1 respectively. Calculate Λ m ° for CH 3 COOH .

Given, The standard molar conductivity for sodium chloride, NaCl = 126 . 4 S cm 2 mol - 1 . The standard molar conductivity for hydrochloric acid, HCl = 425 . 9 S cm 2 mol - 1 . The standard molar conductivity for sodium acetate, CH 3 COONa = 91 . 0 S cm 2 mol - 1 . The reaction between acetic acid and sodium hydroxide is given as, CH 3 COOH + NaCl → CH 3 COONa + HCl . Therefore, the molar conductivity of acetic acid, CH 3 COOH will be calculated as, Λ m ( CH 3 COOH ) ° + Λ m NaCl ° = Λ m CH 3 COONa ° + Λ m HCl ° . Λ m ( CH 3 COOH ) ° = Λ m CH 3 COONa ° + Λ m HCl ° - Λ m NaCl ° . Λ m ( CH 3 COOH ) ° = 91 . 0 + 425 . 9 - 126 . 4 S cm 2 mol - 1 . Λ m ( CH 3 COOH ) ° = 390 . 5 S cm 2 mol - 1 . Thus, the molar conductivity of acetic acid is 390 . 5 S cm 2 mol - 1 .

State the second law of thermodynamics.

The second law of thermodynamics can be expressed in terms of entropy. It can be stated as “the entropy of an isolated system increases during a spontaneous process”. The total entropy change ( ∆ S total ) for the system and the surroundings of a spontaneous process is given by, ∆ S total = ∆ S system + ∆ S surrounding > 0 When a system is in equilibrium, the entropy is maximum and the change in entropy, ∆ S = 0 . Hence, entropy of a spontaneous process increases till it reaches a maximum and at equilibrium the change in entropy is zero.

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EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR CHEMISTRY>Chapter -1 - Electrochemistry>Uttar Pradesh Board-2019>Q 3

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12th Uttar Pradesh Board

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Following four colourless solutions of salts have been kept in different test tubes and a copper strip was dipped in each. Which solution will turn blue in the end?

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