What are maximum boiling azeotropes? Give one example.

A maximum boiling azeotrope, also known as a positive azeotrope, is a type of azeotrope in which the boiling point of the mixture is higher than the boiling points of its individual components. In other words, the azeotropic mixture boils at a temperature higher than the boiling points of its constituent compounds.

One example of a maximum boiling azeotrope is the mixture of hydrochloric acid (HCl) and water (H2O). This azeotropic mixture, often referred to as "aqueous hydrochloric acid," has a boiling point of around 110.4 degrees Celsius (230.7 degrees Fahrenheit), which is higher than the boiling points of pure HCl (approximately -85 degrees Celsius or -121 degrees Fahrenheit) and pure water (100 degrees Celsius or 212 degrees Fahrenheit). The maximum boiling azeotrope forms at a specific composition, which in the case of hydrochloric acid and water is approximately 20.2% HCl and 79.8% water by mass.

It's worth noting that the composition and boiling point of an azeotrope can vary with pressure. The example provided above assumes standard atmospheric pressure (1 atm or 101.3 kPa).