Which of the following methods uses a chemical reaction to separate components of a system? (A) The evaporation of ocean water to obtain sea salt. (B) The use of a magnet to separate iron filings from wood ash. (C) The extraction of copper metal from an ore that contains copper(II) sulfide. (D) The use of a sieve to separate stones from sand. Or (E) the use of paper chromatography to separate plant pigments.
In nature, in everyday life, and in the chemistry laboratory, we are often confronted with systems that are composed of more than one object, more than one substance, or more than one element. For example, the ocean is composed of several things or several components, for example, sand, rocks, shells, corals, plants, fish, and salt water. The ocean is an example of a mixture. A mixture is a combination of different components, such as objects or substances, that are not chemically bonded or joined together. The components can be separated by physical means.
The salt water of the ocean is also an example of a mixture because the water and salt, predominantly sodium chloride, are not chemically joined together but merely mixed or dissolved in each other. A compound, however, is a substance formed when two or more different chemical elements bond together, in other words, a combination of different elements chemically bonded together. The components or elements can only be separated by chemical means, in other words, a chemical reaction. The salt water of the ocean is an example of a mixture containing two different compounds — water, H2O, and the predominant salt of the sea sodium chloride, NaCl.
Taking water as an example of a compound, to separate the components, oxygen and hydrogen, chemical bonds must be broken. It takes a lot of energy to separate the components or elements of a compound in a chemical reaction. This energy is usually supplied in the form of light or heat and sometimes even in the form of energy from sound waves. Less energy is needed to cause physical separation of mixtures. This is because these methods do not require the breaking of chemical bonds. These methods include sieving, evaporation, centrifugation, sorting, chromatography of various kinds, and magnetic separation, just to name a few.
The evaporation of ocean water to obtain sea salt is an example of a physical separation. Using a magnet to pull magnetic iron filings out of wood ash is also a physical separation. Sieving a mixture of sand and stones is a physical separation. And separating a mixture of plant pigments using paper chromatography is also a physical separation because no chemical bonds are broken. However, in the extraction of copper metal from an ore that contains copper(II) sulfide, which is CuS, the bond between the copper and sulfur needs to be broken with a lot of energy. And this is done using a chemical reaction.
Finally, the method which uses a chemical reaction to separate components of a system is the extraction of copper metal from an ore that contains copper(II) sulfide.