Ice Cubes in Alcohol

Alcohol is an organic compound, in which the hydroxyl or the OH group is bound to the saturated carbon atom. Alcohols are derivatives of hydrocarbons in which one or more of the hydrogen atoms in the hydrocarbon have been replaced by a hydroxyl group. The hydroxyl group is also responsible for imparting certain chemical and/or physical properties to the compound.

The four most common alcohols are methanol (CH₃OH), ethanol (C₂H₅OH), propanol (C₃H₇OH) and butanol (C₄H₉OH). These are the simplest alcohols.

How are alcohols formed?

Alcohols can be formed using fermentation.  Fermentation is usually done by using yeast to act on carbohydrates to produce ethanol and carbon dioxide. Rice, malt, fruits etc, which are sources of carbohydrates. They  are used to react with yeast to get alcohol.

Structure of Alcohol:

The molecular structure of liquid alcohol is complex. The molecules in liquid alcohol are not randomly oriented with respect to each other. The angle between the oxygen-hydrogen bonds of two neighbouring alcohol molecules is usually about 120 degrees. Alcohol is an organic molecule containing an -O-H group.

Any molecule which has a hydrogen atom attached directly to oxygen or a nitrogen atom is capable of hydrogen bonding.

Ethanol has a hydrogen atom attached directly to oxygen - and that oxygen has two lone pairs of electrons as in a water molecule. Hydrogen bonding can occur between ethanol molecules, although not as effectively as in water. The hydrogen bonding is limited to only one hydrogen atom in each ethanol molecule with sufficient δ+ charge.

Alcohols with a smaller hydrocarbon chain are soluble in water. This is due to the hydroxyl group in the alcohol which is able to form hydrogen bonds with water molecules. As the length of the hydrocarbon chain increases, the solubility in water decreases. With four carbon in the hydrocarbon chain and higher, the decrease in solubility becomes visible as the mixture forms two immiscible layers of liquid. The reason why the solubility decreases as the length of hydrocarbon chain increases is because it is requires more energy to overcome the hydrogen bonds between the alcohol molecules as the molecules are more tightly packed together as the size and mass increase.

Alcohol and water do not mix completely. When 50 ml of water is mixed with 50 ml of alcohol, the resulting solution is not 100 ml because the alcohol molecules fall to the spaces between the water molecules. There is oxygen between the spaces, so the alcohol molecules push the oxygen out of the spaces and occupy that space.

At the microscopic level, a complete mixing of alcohol and water would entail the two molecules coming together at random to form a single liquid phase without interacting with one another. This means entropy for an alcohol-water solution should substantially increase over the entropy for pure alcohol.

When water is added, the methanol chains interact with water molecule in clusters of different sizes. This bends the chains into stable open-ring structures. The formation of new ordered structures in which both water and methanol molecules take part means that the two liquids mix very little on the microscopic level.

The inter-molecular space in liquid alcohol is more. Therefore, alcohol is less dense. The density of alcohol is 0.789gm/cc. The density of ice is 0.92gms/cc. Therefore density of Alcohol is lesser than the density of ice cubes.  So ice cubes sink in alcohol.