Electrochemistry 3

Question 1

use of Wheatstone bridge

Answer 1

accurate measurement of an unknown resistance can be
performed on a Wheatstone bridge.

Question 2

measuring the resistance
of an ionic solution we face two problems.

Answer 2

• Firstly, passing direct current
  (DC) changes the composition of the solution. The first difficulty is resolved by using an alternating current (AC) source
  of power.
• Secondly, a solution cannot
  be connected to the bridge like a metallic wire or other solid conductor. The second problem is solved by using a specially designed
  vessel called conductivity cell.

Question 3

conductivity cell

Answer 3

Basically it consists of two platinum electrodes coated with platinum
black (finely divided metallic Pt is deposited on the electrodes
electrochemically).

Question 4

Cell Constant

Answer 4

• The quantity l/A is called cell constant denoted by the symbol, G*.
  It depends on the distance between the electrodes and their area of
  cross-section and has the dimension of length–1 and can be calculated
  if we know l and A.
• The cell constant is usually determined by measuring
  the resistance of the cell containing a solution whose conductivity is
  already known.

Question 5

Oscillator

Answer 5

(a
source of a.c. power in the audio frequency range
550 to 5000 cycles per second)

Question 6

conductivity =

Answer 6

cell constant/R