Question #a4ee5
1 Answer
The answer is (a)
Explanation:
The first thing to do here is to write the reduction half-reaction that describes the reduction of hydrogen ions,
#2"H"_ ((aq))^(+) + color(blue)(2)"e"^(-) -> "H"_ (2(g))#
This half-reaction takes place at the cathode. You don't really need to write the oxidation half-reaction to answer this question, so I'll skip that part.
The important part to notice here is that you need
Now, you know that you must produce
So, STP conditions were defined as a pressure of
This means that your electrolysis must produce
#1.12 color(red)(cancel(color(black)("cm"^3))) * (1 color(red)(cancel(color(black)("dm"^3))))/(10^3color(red)(cancel(color(black)("cm"^3)))) * (1 color(red)(cancel(color(black)("L"))))/(1color(red)(cancel(color(black)("dm"^3)))) * "1 mole H"_2/(22.4color(red)(cancel(color(black)("L")))) = 5.0 * 10^(-5)"moles H"_2#
Use the aforementioned mole ratio to calculate the number of moles of electrons needed
#5.0 * 10^(-5) color(red)(cancel(color(black)("moles H"_2))) * (color(blue)(2)color(white)(a)"moles e"^(-))/(1color(red)(cancel(color(black)("mole H"_2)))) = 1.0 * 10^(-4)"moles e"^(-)#
Now, this many moles of electrons must be delivered by the cathode per second. As you know, an ampere is defined as one coulomb per second.
#"1 A" = "1 C"/"1 s"#
One coulomb is simply the magnitude of the charge carried by
#1.0 * 10^(-4) color(red)(cancel(color(black)("moles e"^(-)))) * (6.022 * 10^(23)"e"^(-))/(1color(red)(cancel(color(black)("mole e"^(-))))) = 6.022 * 10^(19)"e"^(-)#
This means that you have
#6.022 * 10^(19)color(red)(cancel(color(black)("e"^(-)))) * "1 C"/(6.242 * 10^(18)color(red)(cancel(color(black)("e"^(-))))) = "9.65 C"#
Therefore, you can say that if you need
#"9.65 C"/"1 s" = color(green)(|bar(ul(color(white)(a/a)color(black)("9.65 A")color(white)(a/a)|)))#
ALTERNATIVELY
You can get the answer a little quicker by using Faraday's constant,
#F = "96,485.33 C mol"^(-1)#
You have
#1.0 * 10^(-4)color(red)(cancel(color(black)("moles e"^(-)))) * "96,485.33 C"/(1color(red)(cancel(color(black)("mole e"^(-))))) = "9.65 C"#
In one second, you will once again get
#"9.65 C"/"1 s" = color(green)(|bar(ul(color(white)(a/a)color(black)("9.65 A")color(white)(a/a)|)))#