Answer to Question #140253 in Chemistry for Dr. Horus

Question

10mg of potassium was deposited when a current of 0.5A was passed through fused potassium chloride for 1.5hr at 25°C. Calculate the electrochemical equivalent of potassium at this temperature.

Answer 1

When the electrolysis by one Coulomb charge $Q$ is performed, the mass of a substance produced at the electrode $m$ equals to the electrochemical equivalent of the substance $Z$ . According to this definition, the electrochemical equivalent can be calculated as:

$Z = \frac{m}{Q}$ .

The charge passed through the system during the electrolysis equals to the product of the current $I$ and time $t$ (remember that 1A =1 C/s, 1 hr=60·60 s):

$Q = It = 0.5 \text{ A}\cdot 1.5·60·60\text{ s} = 2700$ Coulombs (C).

Therefore, the electrochemical equivalent of potassium is (1mg=1·10^-3g):

$Z = \frac{10·10^{-3} \text{ g}}{2700 \text{ C}} = 3.70·10^{-6}$ g/C.

Answer: the electrochemical equivalent of potassium at 25°C is 3.70·10^-6 g/C.