Question

7. Suppose you were given a mixture of n-octane, sodium chloride and water to separate. Using the information gathered for these and similar compounds in this experiment, and using what you know about the properties of these materials from other contexts, outline a procedure that could be used to do a quantitative separation of these three materials. Your procedure should be specific enough, that if followed, someone could determine the mass of each of the three materials present in the mixture.

Answer 1

The mixture contains n-octane, sodium chloride (NaCl) and water. n-octane is non-polar hydrocarbon while NaCl and water are both polar. NaCl is an ionic compound while water is a polar solvent. NaCl dissolves completely in water or a solution of NaCl is completely miscible with water. However, n-octane being non-polar, is immiscible in both NaCl and water.

Solvent extraction strategy can be used to separate n-octane from NaCl and water. n-octane is liquid itself; hence, shake n-octane with the NaCl/water mixture in a separatory funnel until clear separation of phases occur. The two phases are drained out to get almost pure n-octane and NaCl/water mixture. A small amount of anhydrous MgSO₄ is added to the extracted n-octane layer to remove traces of moisture. The technique of solvent extraction must be used multiple times for better efficiency.

The NaCl/water mixture can be distilled to obtain the pure components. The boiling point of pure water is 100⁰C while NaCl boils at a higher temperature. Hence, the mixture of NaCl and water can distilled when the water is boiled off as steam. The steam condenses and collects as pure water in a collecting flask. The distillation flask contains pure NaCl.