Which of the following best describes a solution? (A) The medium into which a substance can be dissolved. (B) A heterogeneous mixture of two or more substances. (C) A mixture of any substance with water. (D) A homogeneous mixture of two or more substances. Or (E) the liquid component of a mixture between two substances.
The question asks about a solution. A solution is an example of a mixture. A mixture is a combination of two or more substances which are not chemically bonded together, where each substance retains distinct identities and properties. There are two broad categories of mixtures: homogeneous mixtures and heterogeneous mixtures. The prefix homo- in homogeneous means the same. Homogeneous mixtures have a composition and properties which are uniform throughout the mixture. If several samples are taken from a homogeneous mixture, they might have different sample sizes. But they will all be composed of the same components and in the same ratio and therefore have the same properties.
In a heterogeneous mixture, however, the prefix hetero- means different or nonuniform. In a heterogeneous mixture, the composition and properties are nonuniform or are different throughout the mixture. If we took several samples from a heterogeneous mixture, they will most likely contain the components in a different ratio in each sample. And therefore each sample will have slightly different properties. Often in a heterogeneous mixture, the different components are visible to the naked eye, for example, a mixture of ice in soda or a mixture of oil and water, whereas when the components of a homogeneous mixture are mixed together, for example, NaCl, sodium chloride or table salt, when it is put into water and stirred, the individual components are no longer visible to the naked eye. The mixture looks uniform throughout.
In this example, we get saltwater. The individual components cannot be distinguished from one another in the resulting homogeneous mixture. The saltwater in our example is called a saltwater solution, with the minor component, in this case sodium chloride, being called the solute and the major component, in this example the water, being called the solvent.
Homogeneous mixtures do not have to be liquid. For example, the air we breathe is a homogeneous mixture of different gases, such as nitrogen gas, oxygen gas, carbon dioxide, argon, and gaseous water or water vapor, as well as other gases. Although composed of gases, air is also called a solution. Since the major component of air, about 78 percent, is composed of nitrogen, we say nitrogen is the solvent. And all the other gaseous components of air which comprise the minor portion of air are the solutes. So the solutes are oxygen, carbon dioxide, argon, water vapor, and all the other remaining gases. The composition is uniform, and the various gases cannot be distinguished from one another.
In the same way, all homogeneous mixtures can be referred to as solutions. When we look at our answer options, we can see that answer option (B), a heterogeneous mixture of two or more substances, does not describe a solution. Although answer option (D), a homogeneous mixture of two or more substances, does describe a solution, we cannot settle on this as our final answer before eliminating all the other answer options, since we are asked which statement best describes a solution. Answer option (A), the medium into which a substance can be dissolved, describes only part of a solution, the major component, in other words, the solvent. So we can rule out answer option (A).
We can also rule out answer option (C), a mixture of any substance with water. Water present in a mixture does not make it homogeneous or a solution necessarily. For example, an oil–water mixture we have seen is heterogeneous and is not a solution. We can also rule out answer option (E), the liquid component of a mixture between two substances, as we have seen that not all homogeneous mixtures are necessarily liquids. We can therefore conclude that answer option (D) is the correct answer.
Which of the following best describes a solution? The answer is (D), a homogeneous mixture of two or more substances.