Video Transcript
A student dissolves some sodium chloride in water and wants to recover it. Which techniques should they use? (A) Crystallization, (B) filtration, (C) centrifugation, (D) evaporation, or (E) distillation.
The question is asking for sodium chloride, also known as table salt, to be recovered or separated from water after being dissolved in it, which means the technique the student will need to use should be a separation technique. As it turns out, all of the answer choices listed are a type of separation technique, each with their own process and application. Let’s use this table to highlight each of their specific uses in order to determine which is the correct answer.
Crystallization and evaporation are separation techniques that can be used to separate a dissolved solid from a liquid. While their general use is similar, the main differences are that evaporation is used when the solution contains only one soluble solute, there are no known impurities, and large crystals are not needed. Crystallization, on the other hand, is used when the solution is known to contain two or more known soluble solutes that have different solubilities, the solution contains impurities, and/or large crystals are needed.
Filtration is a separation technique that can be used to separate an insoluble solid from a liquid. This can be accomplished through gravity filtration, which is typically used for large mixture samples and/or when the mixture needs to be separated while hot, or by vacuum filtration, which is typically used for small mixture samples.
Centrifugation is a separation technique commonly used to separate very fine suspended particles or extremely small solids from a liquid. And finally, distillation is a separation technique that can be used to separate two miscible liquids that have different boiling points.
Now let’s analyze the mixture we need to separate to determine which separation technique would work best. A key point to highlight is that sodium chloride, or table salt, as we know, dissolves in water. More generally speaking, a mixture of table salt and water consists of a dissolved solid in a liquid. This eliminates filtration, centrifugation, and distillation as viable techniques to separate sodium chloride from water because none of these techniques are used to separate a dissolved solid from a liquid. This leaves answer choices (A) and (D) as potential solutions because their separation technique is defined as being able to separate a dissolved solid from a liquid.
In reality, both crystallization and evaporation are viable separation techniques for a sodium chloride-water mixture. However, since sodium chloride is the only solute and there are no other known impurities, it would be more efficient to perform evaporation over crystallization for this solution.
Which techniques should be used to separate sodium chloride from water? The answer is option (D) evaporation.
