Tertiary alcohols do not oxidise with potassium dichromate primarily due to their molecular structure. In oxidation reactions facilitated by oxidising agents like potassium dichromate, the removal of hydrogen atoms from the carbon atom bearing the hydroxyl group is a key step. In tertiary alcohols, this carbon is bonded to three other carbon atoms and does not have a hydrogen atom attached to it. This absence of hydrogen atoms makes it impossible for the typical alcohol oxidation mechanism to proceed. In contrast, primary and secondary alcohols have at least one hydrogen atom bonded to the hydroxyl-bearing carbon, allowing for the removal of hydrogen and subsequent oxidation to aldehydes or ketones, respectively. Therefore, the structural characteristic of tertiary alcohols makes them resistant to oxidation under conditions where primary and secondary alcohols readily oxidise.

The iodoform test is not universally applicable for identifying all types of alcohols. It is specific to alcohols that either are methylated (contain the CH₃CH(OH)– group) or can be oxidised to form methyl ketones. This includes secondary alcohols with at least one methyl group attached to the carbon bearing the hydroxyl group and certain primary alcohols such as ethanol. Tertiary alcohols generally do not give a positive iodoform test, as they lack the necessary structure to form methyl ketones upon oxidation. Similarly, primary and secondary alcohols without the CH₃CH(OH)– group also do not react positively. Therefore, while the iodoform test is a valuable tool for identifying specific types of alcohols, its scope is limited and cannot be used to conclusively identify all alcohol types.

The solubility of an alcohol in water is significantly influenced by its molecular structure, particularly the balance between its hydrophilic (water-attracting) and hydrophobic (water-repelling) parts. Alcohols contain a hydroxyl group, which is hydrophilic due to its ability to form hydrogen bonds with water molecules. However, they also have a hydrocarbon chain, which is hydrophobic. In smaller alcohols like methanol and ethanol, the hydroxyl group dominates, making them highly soluble in water. As the length of the hydrocarbon chain increases, the hydrophobic character becomes more pronounced, decreasing the solubility of the alcohol in water. Primary alcohols tend to be more soluble than secondary and tertiary alcohols of similar molecular weight because the hydroxyl group in primary alcohols is more accessible for hydrogen bonding due to less steric hindrance. Conversely, tertiary alcohols, with bulkier hydrocarbon groups, exhibit lower solubility due to the increased hydrophobic character and hindered hydrogen bonding.

The boiling points of primary, secondary, and tertiary alcohols vary due to differences in their molecular structures and the resulting intermolecular forces. Primary alcohols have the highest boiling points among the three. This is because they have the most hydrogen bonding capabilities, owing to the presence of two hydrogen atoms bonded to the carbon bearing the hydroxyl group. Hydrogen bonds are strong intermolecular forces, and the presence of more of these bonds in primary alcohols leads to higher boiling points. Secondary alcohols have moderately high boiling points as they have only one hydrogen atom attached to the carbon with the hydroxyl group, resulting in fewer hydrogen bonds compared to primary alcohols. Tertiary alcohols, on the other hand, have the lowest boiling points as the carbon bearing the hydroxyl group is bonded to three other carbons and lacks hydrogen atoms for hydrogen bonding. Additionally, the steric hindrance in tertiary alcohols affects the ability of molecules to come close enough to form effective hydrogen bonds, further lowering their boiling points.

Determining the classification of an unknown alcohol can be achieved through a combination of chemical tests and observations. The initial step involves performing the Lucas test, where the alcohol is reacted with Lucas reagent (a mixture of concentrated hydrochloric acid and zinc chloride). Tertiary alcohols react rapidly, forming a cloudy solution or a separate layer, indicating their classification. Secondary alcohols react more slowly, taking several minutes to hours to show cloudiness, while primary alcohols react very slowly or not at all under room temperature. To distinguish between primary and secondary alcohols, the oxidation test with potassium dichromate can be used. Primary alcohols oxidise to aldehydes and then to carboxylic acids, changing the solution colour from orange to green. Secondary alcohols oxidise to ketones without further reaction, showing a less pronounced colour change. Tertiary alcohols do not react, providing a clear distinction. Additionally, the iodoform test can be employed to identify alcohols with the CH₃CH(OH)– group. These methods, when used in conjunction, allow for the accurate classification of an unknown alcohol.