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 Multiple Choice QuestionsShort Answer Type

271. The conductivity of 0.1 M KCl solution at 298 K is 0.0129 s cm–1. The resistance of this solution in a conductivity cell is found to be 58 ohms. What is the cell constant of the cell? The 0.1 M AgNO3 solution at 298 K in the same conductivity cell offered a resistance of 60.5 ohms. What is the conductivity of 0.1 M AgNO3 solution?
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272. Resistance of a conductivity cell filled with 0.1 M KCl solution is 100 £2. If the resistance of the same cell when filled with 0.02 M KCl solution is 520 Ω. Calculate the conductivity and molar conductivity of 0.02 M KC1 solution. The conductivity of 0.1 M KCl at 298 K is 0.0129 s cm–1.
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273. The electrical resistance of a column of 0.05 M NaOH solution of diameter 1 cm and length 50 cm is 5.55 x 103 ohm. Calculate its resistivity, conductivity and molar conductivity.
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274. 250 cm3 solution containing 1 g of Ca(NO3)2 in conductivity cell offered a resistance of 48 ohms. The cell constant of conductivity of the solution is 0.56 cm-1. Find the molar conductivity.
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275. The conductivity of 0.00241 M acetic acid is 7.896 x 10–5 s cm–1. Calculate its molar conductivity and if Λ°m for acetic acid is 390.5 s cm2 mol–1, what is its dissociation constant?
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276. Λ°m for NaCl, HCl and CH3COONa are 126.4, 425.9 and 91.0 s cm2 mol–1respectively. Calculate Λ° for HAC.
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277. The specific conductance of a saturated solution of AgCl in water is 1.826 x 10–6ohm–1 cm–1 at 25°C. Calculate its solubility in water at 25°C. [Given Λm (Ag+) = 61.92 ohm–1 cm2 mol–1 and Λm (CI ) = 76.34 ohm–1 cm2 mol–1]
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278. Calculate the molar conductance at infinite dilution of ethanoic acid from the following data:
Λ°m (HCl) = 425.9 s cm2 mol–1
Λ°m (CH3COONa) = 91.0s cm2 mol–1
Λ°m (NaCl) = 126.4 s cm2 mol–1
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 Multiple Choice QuestionsLong Answer Type

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279. Draw curves to show how the molar conductance of strong electrolytes varies with dilution.


When a plot is drawn between the molar conductivity versus square root of concentration for strong electrolytes, a curve (nearly straight line) shown in the given Fig is obtained. It is clear from the figure that molar conductance has higher value and increases linearly. Slight increase in the value of Λwith dilution is due to the decrease in interionic attraction with dilution i.e., decrease in concentration.

When a plot is drawn between the molar conductivity versus square roo

The molar conductivity at infinite dilution (Λm) can be obtained by extrapolating the above graph of strong electrolytes to zero concentration.
Kohlrausch Law of Independent migration of ions: The law states that limiting molar conductivity of an electrolyte can be represented as the sum of the individual contributions of the anion and cation of the electrolyte. Thus, if λ°Na+ and λCl are molar limiting conductivity of the sodium and chloride ions respectively, then the limiting molar conductivity for sodium chloride is given by the equation:
Λ°NaCl = λ°Na + λCl
In general, if an electrolyte on dissociation gives v+ cations and v anions then its limiting molar conductivity is given by
Λ° = v + λ°+ + V λ°
Here, λ°+ and λ° are the limiting molar conductivities of the cation and anion respectively.
Kohlrausch’s law helps us to calculate
(i) Determination of molar conductivities of weak electrolytes at infinite dilution.
(ii) Determination of the degree of dissociation of electrolytes.
Degree of dissociation: It is ratio of molar conductivity at a specific countraction ‘C’ to the molar conductivity at infinite dilution. It is denoted by α.
i.e.,                   straight alpha space equals space fraction numerator straight A subscript straight m superscript straight C over denominator straight A subscript straight m superscript infinity end fraction

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 Multiple Choice QuestionsShort Answer Type

280. The molar conductivity of KCl solutions at different concentration at 298 K are given below:

C/mol L–1

Λ/s cm2 mol–1

0.000198

0.000309

0.000521

0.000989

148.61

148.29

147.81

147.09

 
Show that a plot between A and C1/2 is a straight line. Determine the values of Λ° and Λ for KCl.
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