Electrochemistry

Question 1

corrosion is caused in saline water give reason

Answer 1

Saline water has extra salts. Nacl, mgcl 2 etc since the concentration of the electrolyte is more ions are present which favors the formation of more electrochemical cell and promotes rusting.

Question 2

Prove that rusting is an electrochemical phenomenon

Answer 2

Since pure iron surface acts as anode and impure surface act as cathode carbon dioxide+ Water, moisture contained in the carbon dioxide act as the electrolyte rusting is an electrochemical phenomenon.

Question 3

alkaline medium inhibits the effect of rusting of iron

Answer 3

Alkaline medium has a OH- which prevent the availability of H+ ions which reduces the oxidation of Fe to Fe2+.

Question 4

Galvanization is more advantageous than tinning

Answer 4

Since the actual potential of ion is lower than 10 tinning is not efficient because ion corrodes at a much faster rate than it does in the absence of tin whereas zinc has a much lower emf than the iron.
The iron article will be protected even if the code is broken or scratches are found. Single continue to get oxidized and protect the iron.

Question 5

batteries discharge more quickly in cold weather give reason

Answer 5

• When the terminals of the batteries are connected a chemical reaction is initiated, it generates the electrons lowering the temperature, causes the chemical reactions to occur slowly, as a result less current is produced.
• When the battery is not in use or if they are refrigerated they get a longer life because at lower temperature, the chemical reactions which causes the leakage of the current at the terminals is low.
• If the batteries is refrigerated, it gets a longer life because the chemical reaction which is due to the leakage of charge at the terminals become low at lower temperature.

Question 6

If there is no salt bridge what will happen?

Answer 6

Electrons given out by the zinc electrode they will flow to the copper electrode and neutralize this Cu2+ ions. therefore sulfate ions will be left and the solution acquire a negative charge.
- At the same time, zinc side zn2+ ions in the zinc sulfate solutions acquire some of the zn2+ which came from the zinc rod and acquire a positive charge. therefore further flow of Electrons will stop and the current stop flowing. and the cell stops functioning.
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Question 7

Functions of saltbridge

Answer 7

• It completes the inner circuit by the flow of ions from one solution to another.
• Salt bridge helps to maintain the electrical neutrality of the solution in the half cell.
• It also avoids the potential difference, which arises between the solutions when they are directly in contact.

Question 8

Drawbacks of standard hydrogen electrode

Answer 8

• Unity concentration of H+ It’s difficult to maintain.
• 1 bar pressure of hydrogen cannot be maintained.
• Platinum gets poisoned very fast when the gas has impurities.

Question 9

Why fuel cells

Answer 9

Primary cells have limited reaction secondary cells take long time to recharge since the combustion reactions are also redox reaction the chemical energy due to combustion of fuel give heat energy. This heat energy is converted to electrical energy.

Question 10

Mercury cell delivers a constant potential during its life time

Answer 10

Overall reaction does not involve any ion whose concentration may change. Hence, it delivers a constant potential during its life time.

Question 11

In the experimental determination of electrolytic conductance, Direct Current (DC) is not used.

Answer 11

Direct current (DC) causes electrolysis of the solution consequently. The concentration of the electrolyte near the electrodes changes and this results in the change in the resistance (and hence the conductance) of the solution. Therefore direct current is not used.