Oxidation reactions of a primary, secondary and tertiary alcohol. Alcohols are classed into three categories based on the number of R groups (carbon chains) bonded to the carbon atom which is itself bonded to the alcohol (-OH) group. Primary, secondary and tertiary alcohols have respectively one, two or three R groups attached to the carbon to which the OH group is attached. When a small amount of acidified dichromate solution (yellow) is added to a sample of each class of alcohol, both the primary and secondary alcohols will oxidise. The primary alcohol oxidises initially to an aldehyde and then to a carboxylic acid. The secondary alcohol oxidises to a ketone. Tertiary alcohols will not oxidise as they do not have a hydrogen atom on the -OH carbon that can be lost in the reaction. Oxidation can be categorised as a loss of hydrogen from a molecule. The colour change here is due to the yellow dichromate ions being reduced to green chromium (III).