Balance the following redox equation using the oxidation number change method. Describe each step that is involved: Al(s) + PbSO4 - - > Al2(SO4)3 + Pb(s)
And what are you stuck on?
http://www.chemteam.info/Redox/Redox-Rules.html
It's a bit tough showing the oxidation number method in this format. Here's the half reaction format...
2Al^o => 2Al^+3 + 2(3e^-)
3Pb^+2 + 3(2e^-) => 3Pb^o
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2Al^o + 3Pb^+2 => 2Al^+3 + 3Pb^o
To balance the given redox equation Al(s) + PbSO4 -> Al2(SO4)3 + Pb(s), we will use the oxidation number change method. This method involves assigning oxidation numbers to all elements in the equation and then balancing the equation by ensuring that the total increase in oxidation number is equal to the total decrease in oxidation number.
Step 1: Assign oxidation numbers to all elements in the equation.
Oxidation numbers are used to keep track of the electron transfer during a redox reaction. For the given equation, we have:
Al(s) - oxidation number = 0 (since it is an elemental form)
PbSO4 - the overall charge of PbSO4 is 0, so the sum of oxidation numbers must be zero. Let's say the oxidation number of Pb is x, the oxidation number of S is y, and the oxidation number of O is z.
So, x + y + 4(-2) = 0
x + y - 8 = 0
x + y = 8
Al2(SO4)3 - let's assume the oxidation number of Al is a, the oxidation number of S is b, and the oxidation number of O is c.
So, 2a + 3(b + 4(-2)) = 0
2a + 3b - 24 = 0
2a + 3b = 24
Pb(s) - the oxidation number of Pb in its elemental form is also 0.
Step 2: Identify which elements are being oxidized and reduced.
In this equation, Al is being oxidized because its oxidation number changes from 0 to +3, and Pb in PbSO4 is being reduced because its oxidation number changes from +2 to 0.
Step 3: Balance the atoms and oxidation numbers separately.
Balance the atoms:
Al(s) + PbSO4 -> Al2(SO4)3 + Pb(s)
2Al(s) + PbSO4 -> Al2(SO4)3 + Pb(s)
Balance the oxidation numbers:
Al(s) -> Al3+
2e- are being lost from Al, so multiply Al by 3 in this half-reaction equation.
Pb2+ -> Pb(s)
2e- are being gained by Pb, so no need to multiply Pb by any coefficient.
Step 4: Balance the charges.
Multiply the Al half-reaction by 2 to balance the number of electrons:
2Al(s) -> 2Al3+ + 6e-
The charges are now balanced, with 6 electrons on each side.
Step 5: Combine the half-reactions.
Add the two half-reactions together and cancel out any common terms:
2Al(s) + PbSO4 -> Al2(SO4)3 + Pb(s)
2Al(s) + PbSO4 -> Al2(SO4)3 + Pb(s)
2Al(s) -> 2Al3+ + 6e-
Pb2+ + 2e- -> Pb(s)
Final balanced equation:
2Al(s) + PbSO4 -> Al2(SO4)3 + Pb(s)
In summary, the steps involved in balancing the redox equation using the oxidation number change method are:
1. Assign oxidation numbers to all elements in the equation.
2. Identify which elements are being oxidized and reduced.
3. Balance the atoms and oxidation numbers separately.
4. Balance the charges.
5. Combine the half-reactions and cancel out any common terms to obtain the final balanced equation.