Question

1. How many grams of chromium metal are plated out when a constant current of 8.00 A is passed through an aqueous solution containing Cr3+ ions for 40.0 minutes?

Answer 1

ion with charge 3⁺, like Cr³⁺ needs 3 Faradays to plate 1 mole 

Amount of electric charge per mole (faraday's constant) = 96500 C mol¹⁻

Time = 40min = 2400 sec

you have coulombs = amps x sec = 8 x 2400 coulombs 

molar mass of Cr = 51.9961g

96500 x 3 coulombs plates 51.9961g Cr 
so 8 x 2400 coulombs gives,

51.9961/(96500 x 3) x 8 x 2400 g Cr = 3.45g Cr 

so, 3.45g chromium metal is plated out.