Video Transcript
Which of the following statements best describes a mixture? (A) A chemical combination of two or more substances. (B) A molecule that is composed of different types of atoms. (C) A nonchemical combination of two or more substances. (D) A substance composed of only one type of atom or molecule. (E) The combination of two substances in different physical states.
This question is asking us to identify which of the statements in the answer choices best describes a mixture. We need to carefully read each answer choice to ensure the statement describes a mixture as accurately and completely as possible.
By definition, a mixture is a physical combination of two or more substances. Let’s begin by examining answer choice (A). Although answer choice (A) states that two or more substances are combined, it also states that the combination is a chemical combination. A mixture is a physical combination of two or more substances. Answer choice (A) is an incorrect answer choice.
Answer choice (B) describes a molecule composed of different types of atoms. An example of a molecule containing different types of atoms is a water molecule. One molecule of water contains two hydrogen atoms and one oxygen atom. Each hydrogen atom is joined to the oxygen atom with a single covalent bond. Because the atoms in the molecule are chemically bonded to each other, they can only be separated by a chemical reaction not a physical process.
In addition, a molecule is a unit of only one substance. A water molecule is the smallest unit of the pure substance water. Every water molecule contains the same ratio of hydrogen to oxygen atoms. This fixed ratio, which in the case of water is two hydrogen atoms for every one oxygen atom, is the reason that water is classified as a compound. A compound is a single pure substance. Remember that a mixture is a physical combination of two or more pure substances. One molecule in a pure substance cannot be a mixture. Answer choice (B) is an incorrect answer choice.
In answer choice (C), the word nonchemical is another word for physical. The statement can be rewarded to a physical combination of two or more substances. This is an accurate description of a mixture. Answer choice (C) is the correct answer choice.
Let’s take a moment to figure out why answer choices (D) and (E) are incorrect.
Answer choice (D) describes a substance made up of one type of atom or molecule. A substance composed of one type of atom is an element. An example of an element is gold. Inside a piece of pure solid gold, we find only gold atoms. Gold is not a mixture; it is one substance, the element gold. Another example of an element is bromine. Bromine is a liquid at room temperature and is composed of diatomic bromine molecules. Even though bromine is composed of molecules, it is classified as an element because all of the atoms are the same.
Another type of pure substance is a compound. A compound is composed of two or more elements in a fixed ratio. Carbon dioxide gas is an example of a compound. Each carbon dioxide molecule contains one carbon atom chemically bonded to two oxygen atoms. All compounds are composed of only one type of molecule. Choice (D) is not a correct answer choice because it describes a pure substance like the elements and compound that we just discussed.
Choice (E) does not tell us if the two substances are combined physically or chemically, but we do know that the two substances have different physical states. Mixtures can be a combination of substances with different physical states. For example, when solid sugar is dissolved into coffee, which is a liquid, sweetened coffee results, which is a mixture. However, mixtures can also form from the physical combination of two substances with the same states. For example, when lemon juice, which is a liquid, is added to water, which is also a liquid, the result is a mixture. Although answer choice (E) does describe a certain type of mixture, mixtures can also be made by combining two substances with the same states. For this reason, answer choice (E) is not a correct answer choice.
Answer choice (C), or a nonchemical combination of two or more substances, is the best description of a mixture.
