Consider the following problem: Al(3+) is reduced to Al(s) at an electrode. If a

Question

Consider the following problem:

Al(3+) is reduced to Al(s) at an electrode. If a current of 2.00 ampere is passed for 48 hours, what mass of aluminum is deposited at the electrode? The reaction ocurs according to the following equation:

Al(3+) + 3e -> Al(s)

What is the correct sequence of the following steps used to solve the problem? The correct answer must be in the form: A, B, C, D, ... (not the corect answer, of course). Pay due attention to spaces.

A: Plug the result of calculation of #mol(Al) in the expression of the requested mass of Al

B: Figure out the number of moles of electrons using the relation between #mol(e), the total charge and the charge of one mole of electrons in the form #mol(e) = ...

C: Set up the expression of the solution to the problem using the relation between mass (wt), number of moles (#mol) and molar weight (MW) of Al in the form wt = ...

D: Plug the result of calculation of total charge in the expression of #mol(e)

E: Figure out the number of moles of Al using the relation between #mol(Al) and the number of moles of electrons (#mol(e)) in the form #mol(Al) = ...

F: Plug the result of calculation of #mol(e) in the expression of #mol(Al)


G: Figure out the total charge using the relation between charge, current and time in the form total charge = ...

Explanation / Answer

Answer –

We are given, current = 2.00 A, time = 48 hours

Reaction - Al3+ + 3e- -----> Al(s)

So, number of electrons transferred, n= 3

First we need to the charge –

We know formula

Electric charge = current * time

We must time in second , so need to convert 48 hr to second

1 hr = 3600 s

So, 48 hrs = ?

= 172800 s

So, charge = 2.00 A * 172800 s

                  = 345600 C

Now we know the 3 moles of electrons transferred means 3 moles of electrons

So total charge in mole of electrons

96485 C = 1 moles of electron

So, 345600 C = ?

= 3.58 moles of electrons

We know, 1 moles of Al formed by gaining 3 moles of electrons means ,

3 moles of electrons = 1 moles of Al

So, 3.58 moles of electrons = ?

= 3.58 moles of electrons * 1 moles of Al / 3 moles of electrons

= 1.19 moles of Al

Now we need to convert this moles of Al in to its mass

Mass of Al = moles of Al * molar mass of Al

                   = 1.19 moles * 26.982 g/mol

                   = 32.2 g of Al

32.2 g of Al is deposited at the electrode.

As per above calculation we can concluded that the steps sequence is

G,D,F,B,A,E,C

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