100 Nano-Stories: Alcohol Properties!
Episode #58: Heat, Solubility, And More!
Preface! ✨
It’s your favorite material science & nanotechnology enthusiast! Yesterday, I gave a brief overview on the fundamentals of alcohols in organic chemistry (not the beer type! 😂)
This article is essential to understand what we will be discussing in this one!
To summarize the main points in the last article,
- Alcohols are basically a methyl group bonded to a hydroxyl group.
- Methyl → “CH3”/“R”. Sometimes a methyl group may be written as “R” instead of “CH3”.
- Hydroxyl → “OH”.
- When naming an alcohol, you use the suffix “ol” at the end of the name in the main carbon chain.
Now that we have the main points clear, let’s move on to the properties of alcohol using a water molecule!
Properties Explained! 💡
Boiling Points & Electronegativity! 🔑
In water, the atoms that make up the molecule are hydrogen and oxygen. The electronegativity of an Oxygen atom is 3.44. The electronegativity of a Hydrogen atom is 2.1. The overall difference in electronegativity is 1.34, so which makes the water molecule polar and has covalent bonds.
Essentially, any molecule that is composed of only oxygen and hydrogen (water) will have polar bonds and be covalent.
Because oxygen has a higher negative electronegativity than hydrogen atoms, the electrons move in closer to the oxygen atom. This allows the water molecule to stick together, making water have a higher boiling point.
However, when we include alcohol such as methanol, the electronegativity of the molecule is quite different. The boiling point of methanol is quite lower because the electronegativity is weaker.
But how, Carlos? 🤔
You can thank the methyl group for the low boiling point!
The electronegativity of a Carbon atom is 2.5. The electronegativity of a Hydrogen atom is 2.1. The overall difference in electronegativity is 0.4, which is less than the required 0.5 difference in electronegativity.
This means that the electrons from the hydrogen atoms will not be pulled towards the carbon atom, and that causes the boiling point to be lower because the hydrogen bonding in the methyl group isn't strong enough.
To summarize boiling points:
- Essentially, any molecule that is composed of only oxygen and hydrogen (water) will have polar bonds and be covalent. This will result in hydrogen bonds that are strong and will result in a higher boiling point.
- Essentially, any molecule that is composed of only carbon or hydrogen will have non-polar bonds and still have covalent bonds. This will result in the electrical charges of the molecule being evenly distributed, and the bonds are weak. This will result in a low boiling point.
- Any alcohol will have a low boiling point because it has a molecule made of only carbon and hydrogen.
Solubility! 🔑
Aerogels start as a wet gel/alcohol, and will sometimes encounter water during the aging process such as ethanol (a catalyst)(more on that in Bonus Resources!) 😄
So what happens to those alcohols/methanol when they encounter water?
When methanol encounters the water molecules, the methanol will dissolve because of hydrogen bonding from the OH Group and the Oxygen Atom in Water!
Hydrogen Bonding is good at bonding any alcohol and water to make them more soluble, but sometimes, longer chains of alcohols will not be able to dissolve in large amounts of water.
For example, if we have alcohol with 10 carbon atoms (a decanol), the entire molecule is non-polar. Non-polar molecules have their electric charges spread evenly, and no positive or negative charges are formed in the molecule. This means that the alcohol won’t be able to undergo hydrogen bonding.
If we were to add larger carbon chains to the alcohol and mix it with water, we will reach a point where only part of the alcohol will dissolve in water, but it will not be able to dissolve in large proportions of water. This means that large carbon chains are not miscible.
Miscible means that two liquids will dissolve to make a substance that looks evenly distributed, homogeneous. This can occur with smaller carbon chains like methanol and ethanol mixed in water.
Immiscible means that two liquids will dissolve, but the mixture won’t be in uniform entirely, you can see the two substances apart from another. This can occur with larger carbon chains like decanol mixed in water.
Closing Thoughts! 💭
Despite alcohol having longer carbon chains, you may be thinking that there will be a lower boiling point, but that is not true!
The more carbon chains in a molecule/alcohol, the boiling point gets higher because you will need to add more heat to break the large carbon chain apart!
But what is the mechanism behind this, Carlos? 💭
See you tomorrow to talk about London Dispersion Forces! ✌🏽
Vocabulary! 📓
Alcohol (organic chemistry) is a methyl group attached to a hydroxyl group.
Methyl → “CH3”/“R”. Sometimes a methyl group may be written as “R” instead of “CH3”.
Hydroxyl → “OH”.
Polar molecules → The electrical charges of the molecule are not evenly distributed. This leads to electronegativity. Essentially, any molecule that is composed of only oxygen and hydrogen (water) will have polar bonds and be covalent.
Non-polar molecules → The electrical charges of the molecule are evenly distributed. No positive or negative charges are formed in the molecule. Essentially, any molecule that is composed of only carbon or hydrogen will have non-polar bonds and still have covalent bonds.
Electronegativity → The chance that a pair of elections will be attached to a certain atom. If the difference between the electronegativity is greater or equal to 0.5, the molecule is polar. If the difference in electronegativity in the molecule is less than 0.5, the molecule is non-polar. Covalent bonds occur at an electronegativity below around 1.7, and ionic bonds occur at an electronegativity equal to or greater around 1.7.
Miscible → Two liquids will dissolve to make a substance that looks evenly distributed, homogeneous. This can occur with smaller carbon chains like methanol and ethanol mixed in water.
Immiscible → Two liquids will dissolve, but the mixture won’t be in uniform entirely, you can see the two substances apart from another. This can occur with larger carbon chains like decanol mixed in water.
Bonus Resources! 💻
Previous “100 Nano-Stories!” 🔖
© 2021 by Carlos Manuel Jarquin Sanchez. All Rights Reserved.