explain why Butane, Propanone and Ethanoic acid have similar molecular mass but different boiling points?

Question

explain these observations by reference to the type of bonding present and/or the forces between organic molecules.

Butane:- molecular mass= 58 B.P= -1
Propanone:- molecular mass=58 B.P= 56
Ethanoic acid:- molecular mass=60 B.P= 118

Answer 1

Butane is a small organic molecule, the carbon and hydrogen bonds are nonpolar meaning the intermolecular forces that hold the molecules together aren't very strong. The term used for this this type of bonding is Van Der Waals bonding. Propanone on the other hand has a ketone functional group. The carbon oxygen bond in this functional group is fairly polar. The polarity of the atomic bond results in a partial positive charge on the carbon and a partial negative charge on the oxygen. When to molecules of propanone are close these opposite charges will attract and create a stronger intermolecular bond than the Van Der Waals bonding. The ethanoic acid has a carboxylic acid functional group which is even more polar than the ketone. This functional group can participate in something called hydrogen bonding. The principle is the same the polarity of the oxygen and hydrogen bond creates a partial negative charge on the oxygen and a partial positive charge on the hydrogen and the carbon. Since the carboxylic acid has more polar bonds it creates more partial electrostatic charges resulting in stronger intermolecular bonding. In relation to boiling points the stronger the intermolecular bonding the higher the boiling point. This is because the molecules need the added energy to break the stronger bonds formed betwen the molecules. Also to determine a bonds polarity (such as the carbon and oxygen bond or the oxygen and hydrogen bond) simply subtract the two elements electronegativity (usually listed on a periodic table). The greater the difference between electronegativities the more polar the bond.

Answer 2

Butane - vdW forces only
Propanone - dipole-dipole attractions
Ethanoic acid - hydrogen bonding.

The stronger the forces, the harder it is to separate the molecules, and the higher the BP.

Answer 3

smileys 10 points 4 da