 Carboxylic acids are found widely in nature. Here are three examples. First up, methanoic acid. Methanoic acid is commonly called formic acid from the Latin for ant. Formica, as it is the compound red ants inject into their prey. It was first isolated by distilling red ants. Secondly, ethanoic acid. Ethanoic acid is commonly called acetic acid from the Latin acetum, meaning sour wine. This is because wine, which is a solution of ethanol, is oxidized in the air to ethanoic acid. Vinegar is a dilute solution of ethanoic acetic acid. Then ethane dioric acid. Ethane dioric acid, commonly called oxalic acid, is toxic and is found in rhubarb leaves and that is why we should never eat them. Carboxylic acids contain the carboxyl group, as shown in the video. This is made up of a carbonyl group and a hydroxyl group. Let's have a look at the reactions of carboxylic acids. Carboxylic acids react as typical acids. These are number one. Acid plus metal goes to salt plus hydrogen. For example, ethanoic acid plus sodium to sodium ethanoate and hydrogen. Number two. Acid and base goes to salt plus water. For example, ethanoic acid and sodium hydroxide become sodium ethanoate and water. And three. Acid plus carbonate go to salt plus carbon dioxide plus water. For example, ethanoic acid and sodium carbonate to sodium ethanoate carbon dioxide and water. Carboxylic acids also give another important reaction called esterification. Here they react with alcohols to give an ester plus water. An example is ethanoic acid and ethanol to ethyl ethanoate and water. This is a reversible reaction, which can be seen from the directions of the two arrows shown. In this reaction, a few drops of concentrated sulfuric acid are added. This sulfuric acid acts as both a catalyst and to remove the water formed, thereby displacing the equilibrium to the right following Le Chatelier's principle. If you don't know this principle yet, no problem. We have a video about it right here just for you. Now, let's take a look at what esters are actually used for. Esters have characteristic smells and are responsible for the flavor of foods and smell of flowers. They are therefore useful as flavorings and perfumes. Some examples of esters together with their smells are three methylbutylethanoate, or bananas, pentyleethanoate, pears, and octyleethanoate, oranges. Animal fats, vegetable fats, and oils are esters of long-chain fatty acids and glycerol. A soap is a salt of a fatty acid. Check out our water and soap video. So, to recap, carboxylic acids contain the carboxyl group. They show the typical reactions of acid. With alcohols, they undergo a sterification to produce esters, and esters are used in the catering and cosmetic industries.