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Fractional distillation is a technique widely used in chemistry for separating mixtures based on the different boiling points of their components. It is particularly useful when the components have boiling points that are relatively close to each other, as is the case with the constituents of air.

In practice, a distillation column is utilized where the liquid mixture is continuously heated. As the mixture warms, the component with the lowest boiling point will start to vaporize first. Once it turns into a gas, it rises through the trays or packing in the column, which are designed to increase the efficiency of the separation by providing more surface area for heat exchange and condensation.

The vapor then reaches the top of the column where it is cooled and condensed back into a liquid. This process effectively isolates the first component. For our specific use case, separating nitrogen from liquid air by fractional distillation makes the most out of the slight differences in boiling points between nitrogen (-195.8°C) and other gases like oxygen and argon.

Understanding boiling points is crucial in the process of fractional distillation. A boiling point is the temperature at which a substance changes from a liquid to a gas. This transition occurs when the vapor pressure of the liquid equals the external pressure on the liquid. For pure substances, this is a fixed temperature under constant pressure conditions.

For example, liquid nitrogen boils at -195.8°C, which is lower than oxygen's boiling point of -183.0°C and argon's -185.9°C. This principle is used to separate nitrogen from the other constituents of air during distillation. The mixture is slowly heated from the lowest boiling point to the highest, allowing for efficient phase changes and collection of the desired component.

As each gas reaches its boiling point, it becomes a vapor and separates from the liquid mixture. By controlling the temperature within the distillation column, one can isolate nitrogen gas efficiently before the other gases begin to evaporate.

Liquefying air is a fundamental step before the fractional distillation process can begin. Air is composed of several gases, including nitrogen, oxygen, and argon, each existing as a gas at room temperature and pressure. To liquefy it, air must be cooled below the boiling points of its major components.

This cooling is often achieved through processes like the Joule-Thomson effect, where a gas cools upon expansion. In simpler terms, when the pressure on a gas is decreased, it expands, leading to a decrease in temperature. By repeating this process, the air is cooled significantly, eventually transitioning from a gaseous to a liquid state.

The liquefied air can then be funneled into the distillation column to begin the separation process. The ability to liquefy air is what enables us to use fractional distillation to isolate nitrogen, a process that is fundamental to industries and scientific research that rely on pure nitrogen gas.