How would one obtain a sample of pure sodium chloride from a mixture of sodium chloride and ammonium chloride?

Answer 1

Heat the solution until a solid crystal appears. Ammonium chloride would be evaporated as ammonia and hydrochloric acid.

The previous answer is incorrect. The procedure given will not produce pure sodium chloride (NaCl) because it will not adequately separate the ammonium chloride (NH4Cl) from the mixture.

If the NaCl/NH4Cl mixture is in solution, don safety glasses and a lab coat then heat the solution on a watch glass and in a fume hood until only wet solids remain. Heating the solution, and especially the solid mixture, outside a properly functioning fume hood will release ammonia and hydrogen chloride gasses and NH4Cl aerosols into the laboratory. Exposure to adequate concentrations of the gasses will cause severe eye, mucous membrane and skin irritation which may require emergency medical intervention!

Next, carefully and slowly heat the wet solids, stirring them occasionally. If too much heat is applied too quickly, the damp solids will spit and pop, launching pieces of the salts in every direction. Continue heating the solids until no more NH4Cl aerosols (smoke) emanates from them. If the original mixture is a solid, heat it the same way.

The remaining solids will be somewhat pure NaCl, however it would need to be recrystallized as many times as necessary until the desired level of purity is realized.

Recrystallize the NaCl by placing it in a flask and adding enough nearly-boiling, demineralized water to just dissolve it. While the solution is still hot and being gently stirred, slowly add 95% or absolute ethyl alcohol only until crystals begin to appear. Allow the flask to sit undisturbed until it is at room temperature, then place it in a refrigerator until throughly chilled. Pour off as much of the supernatant as possible without losing any solids. Filter the solids, wash the filtrate at least twice with ice-cold ethyl alcohol and allow it to completelyair dry. Finally, drive off any remaining interstitial water and alcohol by throughly drying the filtrate in an oven, preferably one that is exhausted. Verify that no ethyl alcohol vapors are detectable from the filtrate by smell and/or visually examine the filtrate for dryness before placing it in an oven. Ethyl alcohol vapors are explosive when the vapor concentration is within the explosive limits!

Answer 2

One way to obtain pure sodium chloride from a mixture of sodium chloride and ammonium chloride is through the process of fractional crystallization. By carefully heating the mixture in water to dissolve the components and then cooling the solution slowly, the less soluble sodium chloride will crystallize out first, allowing for separation from the ammonium chloride.