Chemical Separation by Fractional Distillation and Crystallization

[caption id="attachment_24415" align="alignright" width="480"] Distillation apparatus[/caption] Solids may be subdivided into amorphous solids and crystalline solids. Amorphous solids possess limited order in the way molecules are bonded to each other. Crystalline solids, on the other hand, exhibit an exceptional degree of order. Logic should tell us a mixture of crystalline solids should be capable of chemical separation and purification through some reiterative crystallization process, based on relative solubilities. This proves to be true. The process is called fractional crystallization. Before discussing fractional crystallization, it might prove wise to discuss the simpler process of fractional distillation, the separating by distilling of a mixture of liquids possessing markedly different boiling points. Ordinary Distillation Consider an example of two liquids, Component A and Component B, that are miscible (they dissolve completely one within…
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The Conversion of Cane Juice to Sugar: a Chemical or Physical Change?

Chemistry, Food
[caption id="attachment_24130" align="alignright" width="480"] Harvested sugarcane.[/caption] One of our readers asks, “So, is the crystallization process of cane juice to raw sugar considered a chemical change or a physical change? Why one or the other?” Let’s discuss, starting with an explanation of what constitutes a chemical change. What is a Chemical Change? A chemical compound consists of atoms bonded together in specific fashion to form molecules. When you modify the combination of atoms, you’ve achieved a chemical change. For instance, combine sodium hydroxide with hydrochloric acid, and the result is sodium chloride (table salt) and water, according to the reaction: NaOH + HCl → NaCl + H₂O This example clearly represents a chemical change. Salt (NaCl) is edible, sodium hydroxide or lye (NaOH) is not. Water (H₂O) is safe for…
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