Consider the following substance:
Al2(SO4)3
What is the oxidation number of:
a) aluminum
b) sulfur
c)oxygen
<<<<<<<<<<>>>>>>>>>>>>
First : Al in III A
>>>> Al = 3+
Second : O must be 2-
Third : count and S = 6+
Here is a good site to learn how to do these. Oxygen is -2 for each atom.
http://www.chemteam.info/Redox/Redox-Rules.html
a) Aluminum: Just like a good pair of underwear, aluminum likes to keep it neat and tidy with an oxidation number of +3.
b) Sulfur: Oh, sulfur, you sly devil! It's got a sneaky oxidation number of +6. Watch out for those sulfuric surprises!
c) Oxygen: Ah, the breath of life itself! Oxygen likes to be a rule follower with an oxidation number of -2. It's negative, but in a positively electrifying way!
Let's break down the compound Al2(SO4)3 to determine the oxidation numbers of aluminum, sulfur, and oxygen.
a) Aluminum (Al)
In Al2(SO4)3, there are two aluminum atoms (Al2), but there is no subscript indicating otherwise. Since there are no charges specified, we assume that the compound is neutral. Thus, the total charge contributed by aluminum must be zero.
Let's assign x as the oxidation number of aluminum. Since there are two aluminum atoms, the total charge contributed is 2x. Since the net charge of the compound is zero, the sum of all oxidation numbers is zero.
2x + 3(-2) = 0
Simplifying the equation, we get:
2x - 6 = 0
2x = 6
x = 3
Therefore, the oxidation number of aluminum (Al) is +3.
b) Sulfur (S)
In Al2(SO4)3, there is only one sulfur atom (S). To determine its oxidation number, we can use the overall charge of the sulfate ion (SO4)2-. The charge of the sulfate ion is -2, so sulfur must have an oxidation number that balances out this charge.
Therefore, the oxidation number of sulfur (S) is +6.
c) Oxygen (O)
In Al2(SO4)3, there are four oxygen atoms (O4). Similar to sulfur, we can use the overall charge of the sulfate ion (SO4)2- to determine the oxidation number of oxygen. The charge of the sulfate ion is -2, and there are four oxygen atoms in it. So, the total charge contributed by oxygen is -8, balancing the overall charge of the ion.
Therefore, the oxidation number of oxygen (O) is -2.
To determine the oxidation numbers of the elements in a compound, you generally need to follow a set of rules. Let's go through each element one by one:
a) Aluminum (Al):
The oxidation number of aluminum can be determined by applying the following rules:
1. The sum of the oxidation numbers in a compound must equal the compound's overall charge. In this case, Al2(SO4)3 is neutral, so the sum of the oxidation numbers must be zero.
2. Oxygen typically has an oxidation number of -2 in compounds, unless it is combined with fluorine or in a peroxide.
3. The overall charge of the sulfate ion (SO4) is -2.
Considering the above rules, let x be the oxidation number of aluminum. Since there are two aluminum atoms, the sum of their oxidation numbers is 2x. The oxidation number of sulfur is -2 and there are three sulfate ions, so the sum of their oxidation numbers is -6. Similarly, since there are 12 oxygen atoms (4 from each sulfate ion), the sum of their oxidation numbers is -24.
Using Rule 1, we set up the equation 2x + (-6) + (-24) = 0. Simplifying it, we get 2x - 30 = 0. Solving for x, we find that the oxidation number of aluminum (Al) is +3.
b) Sulfur (S):
The oxidation number of sulfur can be determined similarly:
Since the overall charge of the sulfate ion (SO4) is -2, and there are three sulfate ions, the sum of the oxidation numbers of sulfur is -6.
Using Rule 1, we set up the equation x + (-6) = 0. Solving for x, we find that the oxidation number of sulfur (S) is +6.
c) Oxygen (O):
As mentioned earlier, oxygen typically has an oxidation number of -2 in compounds, unless it is combined with fluorine or in a peroxide. In this compound, each oxygen atom has an oxidation number of -2.
So, to summarize:
a) The oxidation number of aluminum (Al) is +3.
b) The oxidation number of sulfur (S) is +6.
c) The oxidation number of oxygen (O) is -2.