CSIR-NET/JRF 2014 and UPHESC Assistant Professor 2025
Why is gelatin added during polarographic measurements?
- (A) To reduce streaming motion of falling mercury drop
- (B) To decrease viscosity of solution
- (C) To eliminate residual current
- (D) To prevent oxidation of Hg
Correct Answer: (A) To reduce streaming motion of falling mercury drop
Explanation:
In polarography, a phenomenon called a "polarographic maximum" often occurs, where the current rises much higher than the expected limiting diffusion current.
Mechanism: This abnormal peak is caused by the streaming motion (vigorous stirring/vibration) of the mercury surface and the adjacent solution. Adding a small amount of a surface-active substance like gelatin or Triton X-100 coats the mercury drop. This stabilizes the surface, suppresses the streaming motion, and results in a smooth, readable polarogram.
Other factors:
- (C) Residual current is eliminated by using a blank solution or high-purity supporting electrolytes.
- (D) Dissolved oxygen is removed by bubbling nitrogen gas, not by adding gelatin.