Question

A 1.0 L solution of CaF2 was electrolyzed for 17 h to give 99.02 g of calcium. Assuming the minimum voltage needed was available, what amperage would be needed to complete the electrolysis in the given time? How do I do this problem using stoich?

Answer 1

use

current needed=

I= Q/t

where I= current in ampere

Q = Charge in coulomb

t= time in seconds

also use equation

now we require 2 Moles of electrons for one mol of Ca to form

so find how many Ca are formed using N= w/M where( N= number of moles of Ca, w= 99.02 g weight obtained,

M = molar mass of Ca =40 g)

we get N =99.02/40= 2.4755

so moles of electrons= 2*N = 4.951 moles

now charge on this electrons =Q = 4.951 *(1.6 * 10^-19 coloumb), where N_A is avogadro's number = 6.023 * 10²³

use t= 17 h = 17 *60*60 seconds and put these values into I= Q/t

we get I = 7.8 Ampere