What volume of #F_2# gas, at 25 °C and 1.00 atm, is produced when molten #KF# is electrolyzed by a current of 10.0 A for 2.00 hours. What mass of potassium metal is produced? At which electrode does each reaction occur?

1 Answer
Mar 4, 2017

See below:

Explanation:

The +ve ions are discharged at the cathode. The -ve ions are discharged at anode.

Cathode:

#sf(K_((l))^(+)+erarrK_((l)))#

Anode:

#sf(2F_((l))^(-)rarrF_(2(g))+2e)#

The amount of charge in Coulombs which flows in 1 second is the electric current in Amps.

The total charge passed is given by:

#sf(Q=Ixxt)#

Converting hours into seconds we get:

#sf(Q=10.0xx2xx60xx60=7.20xx10^(4)color(white)(x)C)#

We now can find how much fluorine this will discharge.

From the anode 1/2 equation you can see that:

1 mole #sf(F_2)# needs 2 moles of electrons.

The charge carried by 1 mole of electrons = #sf(9.648xx10^(4)color(white)(x)C)#. This is known as the Faraday Constant.

So 1 mole of #sf(F_2)# needs #sf(2xx9.648xx10^(4)=19.296xx10^(4)color(white)(x)C)#

#sf(19.296xx10^(4)color(white)(x)C)# discharges 1 mole #sf(F_2)#

#:.##sf(1color(white)(x)C)# discharges #sf((1)/(19.296xx10^(4)))# moles #sf(F_2)#

#:.##sf(7.20xx10^(4)color(white)(x)C)# discharges #sf((1)/(19.296xxcancel(10^(4)))xx7.2xxcancel(10^(4)))# moles #sf(F_2)#

#sf(=0.37313)# moles #sf(F_2)#

I mole of fluorine has a volume of #sf(24.465color(white)(x)L)# under the conditions given.

#:.#0.3713 moles of fluorine has a volume of:

#sf(24.465xx0.37313=9.13color(white)(x)L)#

From the cathode 1/2 equation you can see that:

1 mole of K needs 1 mole of electrons.

So 1 mole of K needs #sf(9.648xx10^(4)color(white)(x)C)#

#sf(A_(r)[K]=39.098)#

#:.##sf(9.648xx10^(4)color(white)(x)C)# discharges #sf(39.098color(white)(x)g)# K

#sf(1color(white)(x)C)# discharges #sf((39.098)/(9.648xx10^(4))color(white)(x)g)# K

#:.##sf(7.20xx10^(4)color(white)(x)C)# discharges #sf((39.098)/(9.648xxcancel(10^(4)))xx7.2xxcancel(10^(4))color(white)(x)g)# K

#sf(=29.2color(white)(x)g)# K