Describe the process of obtaining nitrogen from liquid air, including chemical reactions involved in removing impurities and the principle of fractional distillation.

let's continue with the questions.

iii) Write an equation for the reaction taking place in flask Q.

• Flask Q contains a solution (likely potassium hydroxide or sodium hydroxide) used to remove carbon dioxide from the air. $$\text{CO}_2(\text{g}) + 2\text{KOH}(\text{aq}) \to \text{K}_2\text{CO}_3(\text{aq}) + \text{H}_2\text{O}(\text{l})$$

iv) Name one impurity present in the nitrogen gas collected.

• Argon (or other noble gases like neon, helium). These gases are unreactive and are not removed by the chemical methods used in this setup.

v) Another student replaced the copper metal with magnesium turnings. Explain why a lower yield of nitrogen was obtained in the syringe.

• Magnesium is a reactive metal that, when heated, reacts with nitrogen gas to form magnesium nitride ($\text{Mg}_3\text{N}_2$). $$3\text{Mg}(\text{s}) + \text{N}_2(\text{g}) \xrightarrow{\text{heat}} \text{Mg}_3\text{N}_2(\text{s})$$ This reaction consumes some of the nitrogen, leading to a lower amount of nitrogen collected in the syringe.

b) Fractional distillation of liquid air produces nitrogen and oxygen as the major products. Describe how nitrogen gas is obtained from the liquid air. (Boiling points $\text{N}_2 = -196^\circ\text{C}$, $\text{O}_2 = -183^\circ\text{C}$)

• Liquid air is warmed gradually. Since nitrogen has a lower boiling point ($-196^\circ\text{C}$) than oxygen ($-183^\circ\text{C}$), nitrogen will vaporize first. The gaseous nitrogen is then collected, leaving the liquid oxygen behind.