Question

A Cr3+(aq) solution is electrolyzed, using a current of 6.10A.

What mass of Cr(s) is plated out after 1.90 days? What amperage is required to plate out 0.250mol Cr from a Cr3+ solution in a period of 8.60h?

Answer 1

(1) \(\mathrm{Cr} 3++3 \mathrm{e}-\mathrm{m} \mathrm{Cr}\)

charge \(=\) x time in s

\(=6.10 \times 1.90 \times 24 \times 3600=1001376 \mathrm{C}\)

Moles of electrons = charge/Faraday constant

\(=1001376 / 96485=10.3786 \mathrm{mo}\rceil\)

Moles of \(\mathrm{Cr}=1 / 3 \times\) moles of electrons

\(=1 / 3 \times 10.3786=3.4595 \mathrm{mo} 7\)

Mass of \(\mathrm{Cr}=\) moles \(\mathrm{x}\) molar mass of \(\mathrm{Cr}\)

\(=3.4595 \times 51.996\)

\(=180 \mathrm{~g}\)

(2) Moles of electrons \(=3 \mathrm{x}\) moles of \(\mathrm{Cr}\)

\(=3 \times 0.250=0.750 \mathrm{mo}\rceil\)

charge \(=\) moles of electrons \(x\) Faraday constant

\(=0.750 \times 96485=72363.75 \mathrm{C}\)

Current \(=\) charge/time in \(\mathrm{s}\)

\(=72363.75 /(8.60 \times 3600)\)

\(=2.34 \mathrm{~A}\)