A current of 4.71 A is passed through a #Pb(NO_3)_2# solution for 1.80 hours. How much lead is plated out of the solution?
2 Answers
Explanation:
Your starting point here will be to use the definition of an ampere to find the charge that passed through the solution in that period of time.
This will allow you to find how many moles of electrons took part in the reaction.
As you know, an ampere is simply a measure of the rate of flow of electric charge. More specifically, an ampere is defined as an electric current one coulomb per second.
#color(purple)(|bar(ul(color(white)(a/a)color(black)("1 A" = "1 C"/"1 s")color(white)(a/a)|)))#
In your case, a current of
This means that you can use the current as a conversion factor to determine that total charge that passed through the solution in
#1.80 color(red)(cancel(color(black)("h"))) * (60color(red)(cancel(color(black)("min"))))/(1color(red)(cancel(color(black)("h")))) * "60 s"/(1color(red)(cancel(color(black)("min")))) = "6480 s"#
You will thus have
#6480color(red)(cancel(color(black)("s"))) * overbrace("4.71 C"/(1color(red)(cancel(color(black)("s")))))^(color(purple)("= 4.71 A")) = "30520.8 C"#
Now, a coulomb is equivalent to the charge of
#30520.8 color(red)(cancel(color(black)("C"))) * (6.242 * 10^(18)"e"^(-1))/(1color(red)(cancel(color(black)("C")))) = 1.905 * 10^(23)"e"^(-)#
To convert this to moles of electrons, use Avogadro's number
#1.905 * 10^(23)color(red)(cancel(color(black)("e"^(-)))) * overbrace("1 mole e"^(-)/(6.022 * 10^(23)color(red)(cancel(color(black)("e"^(-))))))^(color(purple)("Avogadro's number")) = "0.3163 moles e"^(-)#
Now, your solution contains lead(II) cations,
The reduction half-reaction looks like this
#"Pb"_ ((aq))^(2+) + color(red)(2)"e"^(-) -> "Pb"_ ((s))#
Notice that you need
#0.3163 color(red)(cancel(color(black)("moles e"^(-)))) * "1 mole Pb"/(color(red)(2)color(red)(cancel(color(black)("moles e"^(-))))) = "0.15815 moles Pb"#
Finally, to convert this to grams of lead, use the element's molar mass
#0.15815 color(red)(cancel(color(black)("moles Pb"))) * "207.2 g"/(1color(red)(cancel(color(black)("mole Pb")))) = color(green)(|bar(ul(color(white)(a/a)"32.8 g"color(white)(a/a)|)))#
The answer is rounded to three sig figs.
32.76g
Explanation:
It can be easily solved by applying Faraday's law of electrolysis as follows. According to this law we have the following equation.
-
#W=(Exxcxxt)/F ......(1)#
where: -
#W# =Mass (in g ) of an ion discharged at any electrode #E# =Equivalent mass of that ion.#c# = Current Passed in Ampere#t# = time (in sec) during which electricity is passed.#F# = 1 faraday = 96500C.
Here the equivalent mass of
Inserting these values in equation (1) we have
the mass of lead plated out of the solution