Electrons in Moles?

[vexx]

Hi,

I'm doing prac questions for my unit 2 exam and i came across this about a galvanic cell, where the anode is Lead and the Cathode is silver

i) 'after some time the increase in mass at the Silver electrode was found  0.420g, calculate mole'
i got 0.0039 mol.

then these three which i didnt understand:

ii) 'deduce the amount of electrons, in moles, that have been transferred in the circuit'

iii) 'using your above answer, calculate the amount in moles of lead removed from the Pb electrode.'

iv) 'what mass change will have occurred in the lead electrode'

Help would be much appreciated:)

Vexx

[appianway]

I can't be bothered doing the calculations, but I presume this is how you calculate it.

For the Ag+ ions to become solid Ag, they've each got to accept one electron. Therefore the number of electrons flowing in the circuit should be equal to the number of ions changed from Ag+ to Ag... which should be 0.0039 mol (because there's a 1 to 1 molar ratio between the electrons needed and the mole of Ag+ changed to Ag).

The number of moles of lead should be half of that amount, because Pb-> Pb(2+) + 2e, meaning for each Pb atom changed to a Pb (2+) ion, 2 electrons are donated to the circuit. You can also look at the overall redox equation, which is Pb + 2Ag+ -> Pb(2+) + Ag

For part 3, just figure out the number of moles of Pb (as calculated in the above part... it should be 0.0039/2), and multiply this by the molar mass.

[vexx]

^ Thank you! we never learned this in class, but now i know just incase it pops up anyway - much simpler than i expected:)

[Ilovemathsmeth]

This is a 3/4 concept, so it would be really unfair if they test it, despite it being a fairly simple calculation.

Appianway is correct, you need to associate the number of electrons being gained by a silver cation to form silver metal. This is a 1:1 ratio, thus the mole of electrons equals the mole of silver formed, etc.

[vexx]

This is a 3/4 concept, so it would be really unfair if they test it, despite it being a fairly simple calculation.

Appianway is correct, you need to associate the number of electrons being gained by a silver cation to form silver metal. This is a 1:1 ratio, thus the mole of electrons equals the mole of silver formed, etc.

yeah i found out yesterday arvo that we didn't have to do those questions. thanks anyways, i guess i'll already know about this when it next year;)

[Ilovemathsmeth]

Which is good, you have an advantage for unit 4 - already! =)