Topics |
|---|
1. On which electrode ,hydrogen gas is evolved during the electrolysis of molten CaH2 ?
Calcium hydride dissociates into Ca2+ and H- ions on melting .Hydride ion (H - ) undergoes oxidation at the anode to form hydrogen gas .That is why ,hydrogen gas is evolved at anode during the electrolysis of fused CaH2 .
2. Fluorine cannot be prepared from fluorides by chemical oxidation .Why ?
Fluorine is the strongest oxidizing agent due to its highly positive standard potential .Therefore,fluorine has the highest tendency to get reduced to F- .As a result ,F- ion has the least tendency to get oxidised .That is why,fluorine cannot be prepared from fluorides by chemical oxidation .
3. Two metals A and B have reduction potentials of -0.76 V and + 0.34 V respectively.Which of the two will liberate hydrogen gas from dilute H2SO4 ?
The metal which is more electropositive than hydrogen will be able to liberate hydrogen gas from dilute H2SO4.Metals having negative standard potentials are more electropositive than hydrogen.So, metal A will be able to liberate hydrogen from dilute H2SO4 .
4. Sodium reacts with water at room temperature,whereas magnesium decomposes only hot water.Give reasons ?
Sodium is more electropositive than magnesium .
5. The electrode potentials of four metals A,B,C and D are 1.36 V , - 0.32 V , 0.0 V and -1.26 V respectively.Arrange these elements in the decreasing order of reactivity?
A metal having more negative half - cell potential will be more reactive .So the order of reactivity of A , B , C and D is D > B > C > A .
6. Why does silver nitrate solution becomes bluish when copper rod is placed in it ?
Copper (E0 Cu2+/Cu = 0.34 V) is more electropositive than silver (E0 Ag+/Ag = 0.8 V) .Therefore ,copper is able to displace silver from silver nitrate solution .The dissolution of copper in the solution as Cu2+ ions make it bluish .
7. Write the relation between cell potential and equilibrium constant ?
8. Copper sulphate solution (250 mL) was electrolyzed using a platinum anode and a copper cathode .A constant current of 2 mA was passed for 16 minutes .It was found that after electrolysis the absorbance of the solution was reduced by 50 % of its original value .Calculate the concentration of copper sulphate in the solution to begin with ?
The absorbance of the solution is proportional to the concentration ,(Beer's law).Therefore ,the initial concentration of Cu2+ would be double the concentration of Cu2+ after electrolysis.
9.Explain the term Electrode Reaction?
The electron - transfer reactions which take place at the electrodes are called electrode reactions.In a galvanic cell ,
* Anode is the - ve electrode ,and oxidation occurs at the anode
* Cathode is the +ve electrode,and reduction occurs at the cathode .
10. What is a Fuel cell?
A galvanic cell in which the reactants are fed continuously into the cell ,and the products are continuously removed ,is called a fuel cell .
11. Define Faraday's second law of electrolysis?
The masses of different substances,liberated or dissolved by the same amount of electricity are proportional to their equivalent masses .
12.Mention Sign convention for cell emf?
The international convention for the sign of the cell emf is as follows:
" The emf of a galvanic cell is considered positive,if the electrons flow from left to right in the external circuits ."
As per convention ,therefore in a cell with positive cell emf,the left electrode should ge electron rich (anode) and the electrode at the right should be electron - deficient (cathode ).
13. Write down the Nernst equation for the cell reaction?
For the cell reaction,aA + bB → cC + dD,the Nernst equation is ,
14. What is a Conductivity?
Conductivity is also called specific conductivity .It is defined by the relationship,
.
15. What is an Electrochemical series?
The sequential arrangement of various electrodes in the order of increasing standard electrode potentials is called electrochemical series .
* The electrodes with positive electrode potentials show greater tendency towards reduction than the reduction tendency shown by H+.
* The electrodes with negative electrode potential show lesser tendency towards reduction than the reduction tendency of H+ ions .
16. What do you mean by Electrode potential ?
The electrode potential of an electrode is defined as the emf of a galvanic cell in which the electrode on the left is a standard hydrogen electrode ,and that on the right is the given electrode.
Then "the potential of an electrode relative to a standard hydrogen electrode at 298 K,1 atm pressure when the concentration of the ion taking part in the electrode reaction is 1 mol L-1 , is called standard electrode potential".
The standard electrode potential is denoted by E0
17. Define the Electrical work done by a cell?
The electrical work done by a galvanic cell is equal to the total decrease in the chemical free energy ,i.e,
ΔG =- nFEcell
Under standard conditions ,one cen write,
ΔG0 = -nFE0cell
18.What is mean by Net cell reaction?
The net cell reaction can be obtained as follows:
19. What is mean by Primary cells?
Primary cells produce electricity by the virtue of chemical reaction .In primary cells,the reaction occurs only in one direction ,and cannot be reserved .As a result, these cells become dead over a period of time .Primary cells cannot be recharged / reused .Typical primary cells are,Daniell cell .Dry cell and Mercury cell .
20. What is mean by Secondary cells ?
The secondary cells are repeated action cells.The secondary cells can be recharged by passing electricity through them after every use.As a result ,the secondary cells can be used again and again over much longer periods of time.In these cells ,the electrical energy is stored in the form of chemical energy .Therefore ,these cells are also called storage cells or , accumulators .Lead - acid cell ,( or lead storage ),nickel - cadmium cell etc ,are typical secondary cells .
