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 Multiple Choice QuestionsShort Answer Type

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251. Define conductivity and molar conductivity for the solution of an electrolyte.


Conductivity :–
Conductivity of a solution is equal to the conductance of a solution of 1 cm length
and cross section area of 1 square cm.  it may also be define as the conductance of ine centimeter cube of the conductor . It is represented by the symbol Kappa (κ). mathematically we can write
κ = 1/ p
here ρ is resistivity
the unit of K is ohm –1 cm –1 or S cm–1
The conductivity, κ, of an electrolytic solution depends on the concentration of the electrolyte, nature of solvent andtemperature.
 
Molar conductivity:
Molar conductivity of a solution at a given concentration is the conductance of the volume V of solution containing one mole of electrolyte kept between two electrodes with area of cross section A and distance of unit length. Therefore,
Distance is unit  so l = 1
Volume          = area of base × length
So V   = A × 1  = A
Λm       =κA/l
Λm       = κV
Or
Molar conductivity increases with decrease in concentration. When concentration approaches zero, the molar conductivity is known as limiting molar conductivity and is represented by the symbol Ëom.
For strong electrolytes, Λ increases slowly with dilution and can be represented by the equation:
Λm = Ë°m° – A c ½

 
It can be seen that if we plot Λm against c1/2, we obtain a straight line with intercept equal to Ëm° and slope equal to ‘–A’. The value of the constant ‘A’ for a given solvent and temperature depends on the type of electrolyte i.e., the charges on the cation and anion produced on the dissociation of the electrolyte in solution.
 
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252.

On the basis of the standard electrode potential values stated for acid solution. Predict whether Ti4+ species may be used to oxidise FeII to FeIII.
Reaction: E°/V TiIV + e → Ti3+ + 0.01
Fe3+ + e → Fe2+ + 0.77

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253. What are fuel cells? Write the electrode reactions of a fuel cell which uses the reaction of hydrogen with oxygen.
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254.

Predict the products of electrolysis obtained at the electrodes in each case when the electrodes used are of platinum.
(i) An aqueous solution of AgNO3.
(ii) An aqueous solution of H2SO4.

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 Multiple Choice QuestionsLong Answer Type

255. Define the following terms: (i) Cathodic protection, (ii) Electrochemical series, (iii) Cell constant, (iv) Equivalent conductivity, (v) Strong and weak electrolytes.
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256. Explain the working of galvanic cell. How does the electrochemical cell differ from electrolytic cell?
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 Multiple Choice QuestionsShort Answer Type

257. What is normal hydrogen electrode? Discuss its uses.
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 Multiple Choice QuestionsLong Answer Type

258. What is corrosion? What are the factors which affect corrosion?
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259. Distinguish between: (a) Electrolytes and non-electrolytes, (b) Reduction potential and oxidation potential (c) Primary cells and secondary cells, (d) Specific conductivity and molar conductivity.
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260.

The conductivity of 0.01 M solution of acetic acid at 25°C is 1.63 x 10–4 s cm–1. Given:
Λ°m (HCl) = 426 s cm2 mol–1, Δ°m (Na AC) = 91.5 cm2 mol–1
Λ°m (NaCl) = 126.5 cm2 mol–1 Calculate:
(a) the molar conductivity of acetic acid
(b) the degree of dissociation of acetic acid.
(c) the dissociation constant.
 (d) the pH of 0.01 M solution of acetic acid.

 
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