Question

Classify each of the following as element, compound, or mixture. (a) air (b) iron (c) soy sauce (d) table salt

Short answer

Question: Classify the following substances as elements, compounds, or mixtures: (a) air, (b) iron, (c) soy sauce, (d) table salt. Answer: (a) Air is a mixture. (b) Iron is an element. (c) Soy sauce is a mixture. (d) Table salt is a compound.

Step-by-step solution

(a) Classify air

Air is a combination of several gases like nitrogen, oxygen, carbon dioxide, and noble gases such as argon. Since these gases are not chemically combined and can be separated by physical means, air is classified as a mixture.

(b) Classify iron

Iron is a substance that consists of only one type of atom (Fe). It cannot be broken down into simpler substances by chemical means. Therefore, iron is classified as an element.

(c) Classify soy sauce

Soy sauce is a liquid substance made from a mixture of soybeans, wheat, water, and salt. The different components of the soy sauce can be separated through physical means such as filtration. Therefore, soy sauce is classified as a mixture.

(d) Classify table salt

Table salt is a substance composed of two elements, sodium (Na) and chlorine (Cl), which are chemically combined in a fixed proportion to form sodium chloride (NaCl). Since it's formed by the chemical combination of two elements, table salt is classified as a compound.

Key concepts

Element

An element is a fundamental substance that consists of only one type of atom. It cannot be broken down into simpler substances through chemical means. Elements are building blocks for all matter, and each one has unique properties, such as atomic number and weight.

Iron (Fe), from the exercise, is a perfect example of an element. It's a pure substance that is composed of one kind of atom, and this simplicity makes it an essential part of the periodic table, which lists all known elements. With over 100 different elements, they can combine in various ways to create compounds but cannot be transformed into other elements by normal chemical reactions.

Compound

A compound is a substance composed of two or more elements that are chemically combined in a fixed ratio. Compounds exhibit properties that are distinct from those of their individual elements, and they can only be separated into their constituent elements by chemical means.

Table salt or sodium chloride (NaCl), as mentioned in the exercise, is a typical compound, comprising sodium (Na) and chlorine (Cl) in a 1:1 ratio. The process of forming compounds involves chemical reactions that lead to a new substance with its unique characteristics, different from the elements that formed it.

Mixture

A mixture is a physical blend of two or more substances where each substance retains its individual chemical properties. Mixtures can be homogeneous or heterogeneous. A homogeneous mixture has a uniform composition throughout, whereas a heterogeneous mixture does not.

Examples from the exercise, like air and soy sauce, demonstrate mixtures as they contain multiple substances (gases in air or solids in liquid for soy sauce) that are not chemically bonded and can be separated by physical means, such as filtration or distillation.

Pure Substance

A pure substance is a form of matter that has a constant composition and properties throughout the sample. They are classified into elements and compounds, which are chemically homogeneous and maintain a definite set of characteristics.

When we reference pure substances in chemistry, we indicate that no additional impurities, elements, or compounds are within the sample. Iron as an element and table salt as a compound, mentioned in the exercise, are perfect examples of pure substances. Unlike mixtures, they have a consistent formula and cannot be separated into other materials by physical methods.