Unit 9: Topic 10 - Electrolysis and Faraday’s Law Flashcards
State Faraday’s law of electrolysis and explain it using dimensional analysis.
By Faraday’s first law, the mass of the elements deposited at the electrode is proportional to the charge, i.e. m ~ Q. With constant current electrolysis, Q = It, where Q is charge, I is current, and t is the time. Then we have
m = ItM/Fv.
m is the mass liberated from the electrode (in grams), I is the current applied (in Amperes), t is the amount of time the current is applied (in seconds), M is the molar mass of the substance (in g/mol), F is the Faraday’s constant (approximately 96485 s A/mol), and v is the number of free electrons.
A current of 0.15A is passed through an aqueous solution of K2PtCl4. How long will it take to deposit 1.00g of Pt(s)? The molar mass of Pt is 195.1 g/mol.
We use the formula m = ItM/Fv. Since we want to solve for time t, we rearrange to get t = mFv/IM. m = 1.00, M = 195.1, I = 0.15, F = 96485, and v = 2 since the charge of platinum here is +2. Solving gives t = 6594s.