Re: What is the boiling temperature of sugar?

hi Kelly,

By sugar, I guess you mean common household sugar. The chemical name for this sugar is sucrose. It is a disaccharide, which means that it is made up of two simpler sugars joined together. These simple sugars are called glucose and fructose.

The reason that you couldn't find a boiling point for sucrose is because - it doesn't have one! How can that be? Let's think about what happens when you heat a solid such as sucrose. At a certain temperature (and pressure), the forces that hold the sugar crystals together are overcome, the sugar molecules move apart and the solid turns to liquid. This is called melting. For many substances, further heating pushes the molecules even further apart until they break free from one another and form gas. This is what we call boiling. For a given substance, we can represent the changes from solid to liquid to gas at different temperatures and pressures in a picture called a phase diagram. Here's what a typical phase diagram looks like.

So why doesn't sucrose boil? The answer is that as we raise the temperature further, the sucrose changes chemically so that it isn't sucrose anymore. Before it can boil, the sugar molecules begin to break apart into fructose and glucose and then all sorts of complex reactions happen due to the presence of air and impurities in the sugar. This forms a complex mixture of sugars with a brown colour which you would recognise - it's called caramel.