ThermoChemistry

Question

Calculate the grams of Ca(s) produced when 1.65 Amperes are passed through the cell shown below for 4.96 hours.

Ca^+2(aq) + 2Cl^−1(aq) → Ca(s) + Cl_2(g)

I originally got 6.13 but that is completely wrong. I'm confused and need some help.

Answer 1

1.65 amps = 1.65 coulombs/sec

converting 4.96 hours to sec, we have ... 4.96 hrs x 60 min / hr x 60 sec / min = 17,856 seconds

converting 1.65 amps to coulombs we have ... 1.65 C/sec x 17,856 sec = 29,462 Coulombs

Now, it takes 96,485 coulombs for each mole of electrons, so we need to find moles of electrons equal to 29,462 coulombs:

29,462 C x 1 mol e- / 96.485 C = 0.305 mols e-

For Ca2+ to go to Ca, it requires 2 mols electrons per mole of Ca deposited.

0.305 mols e- x 1 mol Ca / 2 mols e- = 0.153 mols Ca

mass Ca = 0.153 mols Ca x 40 g / mol = 6.11 g Ca (Not so different from what you got. Why is it completely wrong?)