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Electrochemistry · Question 66

AIPMT 2001MCQEasy📈 Topic in 12% papers+4−1
1

The most convenient method to protect the bottom of ship made of iron is

  1. coating it with red lead oxide
  2. white tin plating
  3. connecting it with Mg block
  4. connecting it with Pb block

Answer

(3) connecting it with Mg block

Solution

As per NCERT, corrosion of iron can be prevented by sacrificial protection: iron is covered with or connected to a more active metal (such as Mg or Zn), which is oxidised in preference to iron.

E Mg2+/Mg = -2.37 V is far more negative than E Fe2+/Fe = -0.44 V, so a magnesium block connected to the hull corrodes instead of the iron, and it is easily replaced.

Tin and lead are less active than iron; once their coating or contact is broken, iron corrodes even faster. A paint layer of red lead wears off in sea water.

The most convenient method is connecting the ship's bottom with an Mg block.

Answer: (3)

AIPMT 2001

Keep practising — Electrochemistry

2

Cell reaction is spontaneous when

  1. is negative
  2. is positive
  3. E red is positive
  4. E red is negative
AIPMT 2000
3

Ionic conductances of Ba2+ and Cl- ions at infinite dilution are 127 and 76 ohm-1 cm2 mol-1 respectively. Equivalent conductance of BaCl2 at infinite dilution is

  1. 139.5
  2. 101.5
  3. 203
  4. 279
AIPMT 2000
4

For the disproportionation of copper 2Cu+ Cu2+ + Cu, E is (Given E for Cu2+/Cu is 0.34 V and E for Cu2+/Cu+ is 0.15 V.)

  1. 0.49 V
  2. -0.19 V
  3. 0.38 V
  4. -0.38 V
AIPMT 2000

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