When studying chemistry, one important concept that comes up repeatedly is the oxidation number, also called the oxidation state. This refers to the charge an atom would have if all bonds to atoms of different elements were broken, and the shared electrons were assigned to the more electronegative element. In organic chemistry, it’s essential for understanding how molecules like alcohols, aldehydes, or other functional groups react.
In this blog post, we will explore how to determine the oxidation number of the atoms in C₂H₄O (ethanol), a simple organic molecule commonly known as alcohol.
Step-by-Step Process to Find Oxidation Numbers
1. General Rules for Assigning Oxidation Numbers:
Before diving into the specifics of ethanol (C₂H₄O), let’s recall a few basic oxidation number rules:
- The oxidation number of an atom in its elemental form is always 0.
- For monoatomic ions, the oxidation number is equal to the charge of the ion.
- Hydrogen typically has an oxidation number of +1 when bonded with non-metals, and -1 when bonded with metals.
- Oxygen usually has an oxidation number of -2 (except in peroxides where it’s -1).
- The sum of the oxidation numbers in a neutral compound is always 0.
Now, let’s apply these rules to ethanol.
Breaking Down the Molecular Formula of C₂H₄O
C₂H₄O consists of:
- 2 carbon (C) atoms
- 4 hydrogen (H) atoms
- 1 oxygen (O) atom
Oxidation Number of Oxygen:
Oxygen in ethanol typically follows its general rule of an oxidation state of -2.
Oxidation Numbers of Hydrogen:
Each hydrogen atom in C₂H₄O is bonded to carbon, so each hydrogen will have an oxidation number of +1.
Oxidation Numbers of Carbon:
The trickiest part is determining the oxidation number of carbon. Ethanol contains two carbon atoms, and they are connected as follows:
- One carbon is part of a –CH₂OH group (hydroxymethyl group), where it is bonded to one hydrogen, one hydroxyl group (–OH), and another carbon.
- The second carbon is bonded to two hydrogen atoms and to the first carbon.
To balance the oxidation numbers of the entire molecule (which must sum to 0), we use the following approach:
Solving the Equation
Let’s assign the oxidation number of carbon as x.
- For the –CH₂OH group, one of the carbon atoms (attached to the hydroxyl group) will have an oxidation number of -1.
- The second carbon, which is part of the alkane chain, will have an oxidation number of -2.
Now, let’s check the sum of oxidation numbers for the entire molecule:
- The oxidation number of oxygen is -2.
- The oxidation numbers of hydrogen are +1 each, so for four hydrogens, the total is +4.
- For the two carbon atoms, the sum of the oxidation numbers is -2 (for the –CH₂OH group) + (-2) (for the second carbon).
Now let’s sum them all up:
- C + C + H + H + H + H + O = 0
- (-2) + (-1) + 4 + (-2) = 0
This satisfies the equation, confirming that the oxidation numbers are correct.
Conclusion: The Oxidation Numbers of C₂H₄O
- Carbon (C) in ethanol has oxidation numbers of -2 and -1.
- Hydrogen (H) has an oxidation number of +1.
- Oxygen (O) has an oxidation number of -2.
By understanding the oxidation number concept, we can also learn more about the molecule’s reactivity, its ability to be oxidized or reduced, and its role in different chemical reactions, such as those involving alcohols.
This basic analysis of ethanol serves as an example of how oxidation numbers can be applied in organic chemistry. Whether you’re studying alcohols or more complex molecules, this method is a great starting point to uncover the chemical properties and reactivity of a compound!