Question

Classify each of the following as a mixture or a pure substance. a. water f. uranium b. blood g. wine c. the oceans h. leather d. iron i. table salt e. brass Of the pure substances, which are elements and which are compounds?

Short answer

Water, iron, uranium, and table salt are pure substances. Blood, the oceans, brass, wine, and leather are mixtures. Among the pure substances, water and table salt are compounds while iron and uranium are elements.

Step-by-step solution

Classify each substance as a pure substance or mixture

Based on the definitions we discussed, we can classify each substance as follows: a. water - Pure substance b. blood - Mixture c. the oceans - Mixture d. iron - Pure substance e. brass - Mixture f. uranium - Pure substance g. wine - Mixture h. leather - Mixture i. table salt - Pure substance

Identify pure substances as elements or compounds

Now, we will identify the pure substances found in Step 1 as either elements or compounds: a. water (H2O) - Compound (formed by hydrogen and oxygen) d. iron (Fe) - Element (cannot be broken down into simpler substances) f. uranium (U) - Element (cannot be broken down into simpler substances) i. table salt (NaCl) - Compound (formed by sodium and chlorine) In conclusion, water and table salt are compounds, while iron and uranium are elements. The other substances are mixtures.

Key concepts

Elements and Compounds

In the world of chemistry, pure substances can be divided into two main categories: elements and compounds. An element is a substance that cannot be broken down into any simpler form by chemical means. This means that elements consist of only one type of atom. A good example is iron (Fe) or uranium (U), which consist of only iron and uranium atoms respectively. These elements make up the building blocks of all matter around us.

Compounds, on the other hand, are pure substances that contain two or more different types of atoms, chemically bonded together. They have unique properties that are different from the individual elements they are composed of. For instance, water (H\(_2\)O) is a compound made from hydrogen and oxygen atoms. Neither hydrogen nor oxygen alone can display water’s properties, but combined, they form a new substance. Similarly, table salt (NaCl) is formed by the combination of sodium and chlorine atoms, creating the salty compound we use daily in our meals.

Classification of Matter

Matter is everything that occupies space and has mass. It can be classified broadly into mixtures and pure substances. Understanding the difference between these is crucial for anyone studying chemistry or related sciences.

• Pure Substances: These are materials that have a constant composition and consistent properties throughout the sample. They can be either elements or compounds as mentioned before.
• Mixtures: These consist of two or more substances physically combined. Unlike pure substances, mixtures can have variable compositions. They can further be classified as either homogeneous or heterogeneous.

Homogeneous mixtures, like wine, are uniform throughout whereas heterogeneous mixtures, like blood or oceans, have a non-uniform composition. The properties of mixtures can vary depending on the proportion of their components, making them distinctly different from pure substances.

Chemical Composition

Chemical composition refers to the identity and ratio of the elements that constitute a substance. Knowing the chemical composition helps in identifying if the substance is an element, a compound, or part of a mixture.

• Elements: Their chemical composition is straightforward as they consist only of one type of atom. For instance, the element iron is solely made up of Fe atoms.
• Compounds: They have a fixed, well-defined chemical composition represented by a chemical formula. For example, water's chemical formula is H\(_2\)O, consisting of two hydrogen atoms and one oxygen atom in each molecule.

In mixtures, the chemical composition is not fixed and can vary based on the amount of each ingredient. For instance, in brass, which is a mixture of copper and zinc, the proportion of each element can change. Understanding the chemical composition of substances helps to manipulate them for practical applications, ranging from creating new materials to processing food products.