Question

Calculate avogadro's constant given amp and time and balanced redox reaction

Answer 1

Answer:

avogadro's constant =6.023×10^23

Answer 2

Electrochemistry and Stoichiometry

Charge and Current

In electrochemistry, we are often interested in the number of electrons that have flowed through our cell. This is then related to the mass of the reactants consumed or products formed. However, we generally don't measure charge in the lab. Instead, we measure current.

\[\rm{current = {charge \over time}}\]

Current is the amount of electrical charge that flows during a period of time. Typically we measure this in units of Amperes or Amps. Where 1 Amp (A) = 1 Coulomb (C) per second (s)

\[\rm{Ampere = A = {Coulomb \over second}={C \over s} }\]

We can rearrange this relationship to find the time it takes to get a certain charge with a particular current or the total charge from a current flowing for a given time. Or we could use the charge and time to calculate the current. You should be able to manipulate this in any way given two of the variables to find the third.

Faraday's Constant

In keeping track of how much chemistry is taking place in an electrochemical cell, we have a great advantage since we can direct and measure the exact amount of electric current that flows through the cell (thanks to the wonders of electrical measurement).

So we need a means by which we can convert charge to numbers of electrons.

For this we use Faraday's Constant, \(F\). Faraday's Constant is given the symbol \(F\) and is defined as the charge in coulumbs (C) of 1 mole of electrons. Faraday's constant is approximately 96485 C mol-1. You can calculate \(F\) by multiplying the charge on one electron (1.602 x 10-19) by Avogadro's number (6.022 x 1023).

So imagine we have the following electrochemical cell

Zn | Zn2+ || Ag+ | Ag

How much charge will flow through the cell if 5 g of zinc react? For this we need the balanced electrochemical equation. For the potentials, all we needed was to identify the half-reactions. For stoichiometry we need a balanced equation. For this cell, the balanced equation is

\[\rm{Zn(s) + 2Ag^{+} \rightarrow Zn^{2+} + 2Ag(s)}\]

In addition, we need to realize that the number of electrons that are flowing per zinc is 2 (it is the number of electrons that cancelled out in the overall balanced reaction). We can figure this out using oxidation numbers. Zn is going from 0 to a +2 oxidation state. This is most obvious if you write out the two balanced half-reactions

\[\rm{ox: Zn(s) \rightarrow Zn^{2+} + 2e^-}\]

\[\rm{red: [{Ag^+ + e^- \rightarrow Ag(s)}] \times 2}\]

For this reaction, we would say the number of electrons, \(n\), is two. For every mole of zinc that reacts, it produces two moles of electrons. For every mole of electrons we have \(F\) coulombs of charge.

hope it's helpful