Electrochemistry(XII Std) Important Questions Answers

Answers are given in the end

1.What is NFE/SHE ?

2.Explain the variation of conductivity with dilution. or How does conductivity varies with dilution ? Explain the reason for the variation ?

3.Explain the variation of molar conductivity of weak electrolyte with dilution. or How does conductivity of weak electrolyte varies with dilution ? Explain the reason for the variation ?

4.Explain the variation of molar conductivity of strong electrolyte with dilution. or How does conductivity of strong electrolyte varies with dilution ? Explain the reason for the variation ?

5.Explain Kohlrausch law

6.Calculate the Vont hoff’s factor for K4[Fe{CN)6] .

7.What is cell constant ?

8.Why can’t molar conductivity at infinite dilution of weak electrolyte be measured using graphical method ?

9.What are the secondary cells?

10. What are the fuel cells?

11.State advantages and disadvantages of fuel cells.

Answers- 1.The hydrogen electrode at 298 K with pressure of hydrogen is 1 bar and concentration of hydrogen is 1 M is called Standard Hydrogen Electrode / Normal Hydrogen Electrode.         2.Conductivity decrease with dilution because number of ions decreases per unit volume with dilution. ( Conductivity is the conductance of solution of unit volume/ one litre.                3. Molar conductivity of weak electrolyte increases with dilution due to increase in degree of dissociation.  4.Molar conductivity of strong electrolyte increases with dilution due to decrease in interionic attraction as interionic distance increase with dilution.  5.At infinite dilution molar conductivity of weak electrolyte is sum of contribution of molar conductivities of cations and anions which are independent of each other. 6. Von,t Hoff factor = 5/1 =5.  7. Cell constant is the ratio of length between vs area of electrode = L / A 8.Because line of graph never touch molar conductivity axes. 9.The cell which can be reuse again and again by charging. 10. The cell which generate energy from fuel without burning it , is called fuel cell. 11. Advantage of fuel cell-(1) It is pollution free (2) Continuous source of electricity (3) byproduct is water. Disadvantages of fuel cell- It is costly as catalysts is costly.

Coordination Compounds-IUPAC Names

There are three types of coordination compounds

A. Simple Cation and Complex anion. Example- K4 [Fe (CN)6]

B. Complex Cation and Simple anion. Example- [ Cr {NH3)6] Cl3

C. Complex Cation and Complex anion. Example- [ Cr {NH3)6] [Co (CN)6]

1. Always write the name of cation first and anion later

2.Naming of complex entity

Names of Ligands in alphabetical order + name of metal atom/ion (add ’ate’ if complex is anion) + (Oxidation Number in Roman Numerals)

EXAMPLES-

K4 [Fe (CN)6] Potassium hexacyanoferrate (II)

[ Cr {NH3)6] Cl3 Hexaminechromium (III) chloride

[ Cr {NH3)6] [Co (CN)6] Hexaminechromium(III) hexacyanidocobaltaate(III)

[ Cr (NH3)Br(ox) ]  Aminebromidooxalatochromium(III)

d and f Block Elements – Important Questions and Answers

1. Why are transition metals ions are coloured ?

2.Transitions metals are good catalyst. Why ?

3.Transition metals form alloy. Why ?

4. Why is a dip at Mn in the graph of melting point verses atomic number ?

5. What is lanthanoid contraction ?

ANSWER-

  1. due to d-d transition
  2. A. Due to having variable valences B. Due to having free valencies on surface.
  3. Due to having similar atomic sizes.
  4. Due to weak metallic bond beacuse of half filled electronic configuration.
  5. Decrease in the atomic size of Lanthanoids with atomic number

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