In organic chemistry, oxidation is the addition of oxygen or the removal of hydrogen. In equations the oxidising agent is shown as [O].Acidified potassium dichromate(VI) is the usual oxidising agent. The orange dichromate ions are reduced to green Cr3+ ions.Primary alcohols are oxidised to aldehydes when the product is distilled off as it forms, and to carboxylic acids when heated under reflux. Secondary alcohols are oxidised to ketones. Tertiary alcohols are not oxidised.Combustion is also oxidation. Complete combustion of a hydrocarbon gives carbon dioxide and water and is highly exothermic.