This set of Chemistry Assessment Questions for Schools focuses on “Conductance of Electrolytic Solutions”.
1. The voltameter is an instrument in which electrical energy is converted to chemical energy.
Explanation: The voltameter is a scientific instrument used to measure the quantity of electricity through electrolytic action. Since it is a type of electrolytic cell, it uses electrical energy in order to perform electrolysis. Therefore, it converts electrical energy to chemical energy.
2. Which of the following solutions cannot conduct electricity?
a) Sugar in water
b) NaCl in water
c) MgCl2 in water
d) KCl in water
Explanation: For a solution to conduct electricity, it requires the solution to have movable ions. A solution of sugar in water does not conduct electricity as the sugar molecules do not dissociate to form ions. Whereas the salts in the other options dissociate to form ions and help conduct electricity.
3. Which of the following scientists stated that the equivalent conductivity of an electrolyte at infinite dilution is equal to the sum of the conductances of the ions and cations?
a) Svante Arrhenius
b) Friedrich Kohlrausch
c) Hermann Kolbe
d) Antoine Lavoisier
Explanation: Friedrich Kohlrausch was a German scientist who conducted research on the conductive properties of electrolytes. He stated that “at infinite dilution, each ion of an electrolyte contributes a characteristic ionic conductance towards equivalent conductance of electrolyte which is independent of the nature of the other ion present in the solution”.
4. Which of the following statements is correct with respect to electrolytic solutions?
a) Its conductance increases with dilution
b) Its conductance decreases with dilution
c) Its conductivity increases with dilution
d) Its equivalent conductance decreases with dilution
Explanation: Conductance is dependent on the concentration of the electrolytic solution. It is also inversely proportional to the conductivity of the solution. On dilution, the number of ions per unit volume reduces, decreasing conductivity and increasing the conductance. The equivalent conductance increases on dilution ionic mobility increases on dilution.
5. The limiting equivalent conductance for weak electrolytes can be calculated using Kohlrausch’s law.
Explanation: According to Kohlrausch’s law, the equivalent conductivity of an electrolyte at infinite dilution is the sum of two values one depending upon the cation and the other upon the anion. Therefore, it can be used to calculate the limiting equivalent conductance for weak electrolytes.
6. Which of the following statements is correct regarding the conductivity of solutions of electrolytes?
a) It is independent of the size of the ions
b) It is independent of the viscosity of the solution
c) It depends on the solvation of ions present in solution
d) It decreases with temperature
Explanation: Conductivity of a solution is inversely proportional to the size of the ions present in it, the viscosity of the solution and the solvation of the ions in the solution. Conductivity increases with temperature as it can cause an increase in the number of ions in solution.
7. Which of the following solutions has theleast value of conductivity?
a) 0.01M Na2SO4
b) 0.01M NaCl
c) 0.01M CH3COOH
d) 0.01M HCl
Explanation: The conductivity of a solution depends on the strength of the ions that make up the solution because strong electrolytes dissociate easily and increase the number of ions, increasing the conductivity of the solution. Since CH3COOH is not a strong electrolyte, and because all of the solutions have the same concentration, it has the least value of conductivity.
8. What is the value of the cell constant when the conductance of an electrolytic solution is equal to its conductivity?
Conductance = conductivity
We know that, conductivity = conductance x cell constant
Since the value of conductivity is equal to conductance, the value of the cell constant is equal to 1.
9. Which of the following conditions are satisfied when the electrolytic solutions are infinitely dilute?
a) Electrolyte is 100% dissociated
b) Interionic effects increase
c) Conductance is infinite at infinite dilution
d) Molecules continue to exist in solution
Explanation: At infinite dilution, even weak electrolytes behaves like strong electrolytes and undergo complete ionization. Hence, the electrolyte is 100% dissociated. Also, at infinite dilution, the ions are far apart and interionic effects disappear.
10. Which of the following salts show maximum value of equivalent conductance in their fused state?
Explanation: On moving down a group, the atomic size of the elements increases and so their covalent character also decreases. Thus, CsCl, being the least covalent compound will readily give its ions in its fused state. Therefore, CsCl has the maximum value of equivalent conductance in its fused state.
11. Which of the following is an additive property?
a) Surface tension
Explanation: An additive property is a property which is equal to the sum of corresponding properties of its constituent atoms. In the given list, viscosity, surface tension and volume are not additive properties since it does not depend on the interactions of molecules whereas conductance does. Therefore, conductance is an additive property.
12. Which of the given solutions have an equal value of molar conductivity and equivalent conductivity?
a) 1M BaSO4
b) 1M KCl
c) 1M BCl3
d) 1M CaSO4
Explanation: We know that for electrolytic solutions, ⋀M = ⋀E × valency factor
Where ⋀M = molar conductivity and ⋀E = equivalent conductivity
For KCl, the valency factor is 1. Therefore, for KCl, the value of molar conductivity is equal to its equivalent conductivity. For other ions, ⋀M > ⋀E as their valency factors are > 1.
13. Which of the following is ionic mobility independent of?
a) Size of ion
b) Charge on ion
c) Distance of separation between the electrodes
d) Concentration of electrolyte
Explanation: Ionic mobility is an inherent property of the electrolytic solution and is hence, independent of the distance of separation between the two electrodes. As the charge to size ratio increases, the ionic mobility decreases.
14. Which of the following statements is true regarding ionic speed?
a) It is independent of the size of the ion
b) It depends on the potential difference between the two electrodes
c) It is independent of the concentration of the electrolyte
d) It is independent of the charge of the ion
Explanation: Ionic speed is the speed with which the ion moves in the electrolyte during current passage. It depends on the nature of the ions, potential difference, separation between the electrodes and the concentration of the electrolyte. The ionic speed is directly proportional to the potential difference between the electrodes.
15. Which of the following complex compounds will have minimum conductance in solution?
Explanation: Electrolytes that ionise in solution have a higher value of conductance. Among the given options, [Co(NH3)3Cl3] does not ionise, whereas the other complexes ionise. Therefore, [Co(NH3)3Cl3] will have minimum conductance in solution.
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