Question

Basic Electricity - e.m.f of cadmium standard cell

Answer 1

The electromotive force (e.m.f) of a cadmium standard cell, also known as the Weston cell, is approximately 1.0186 volts at 20 degrees Celsius (68 degrees Fahrenheit). This cell was historically used as a precise source of voltage in laboratories for calibration and standardization purposes.

The Weston cell consists of a cadmium electrode immersed in a cadmium sulfate solution and a mercury amalgam electrode in contact with a saturated solution of mercurous sulfate. The half-reactions occurring at the electrodes are:

At the cadmium electrode:
Cd(s) → Cd²⁺(aq) + 2e⁻

At the mercury amalgam electrode:
Hg₂²⁺(aq) + 2e⁻ → 2Hg(l)

The overall cell reaction is:
Cd(s) + Hg₂²⁺(aq) → Cd²⁺(aq) + 2Hg(l)

The standard e.m.f of the Weston cell is quite stable over time, making it a valuable tool for accurate voltage references in laboratories. However, due to the toxicity of mercury and the development of more stable and environmentally friendly voltage standards, the use of the Weston cell has declined in recent years in favor of other methods.

Remember that practical measurements might differ slightly due to factors like temperature, impurities, and other experimental conditions.