Question

Classify each of the following as a pure substance or a mixture. If a mixture, indicate whether it is homogeneous or heterogeneous: (a) air, (b) tomato juice, (c) iodine crystals, (d) sand.

Short answer

(a) Air is a homogeneous mixture, (b) Tomato juice is a heterogeneous mixture, (c) Iodine crystals are a pure substance, and (d) Sand is a heterogeneous mixture.

Step-by-step solution

(a) Air

Air is a mixture of various gases such as nitrogen, oxygen, carbon dioxide, and other trace gases. Since the composition of these gases is uniform throughout, it is considered a homogeneous mixture.

(b) Tomato Juice

Tomato juice is composed of water, tomato solids, and other dissolved substances. The composition may not be uniform throughout, as solids can settle at the bottom over time. Therefore, it is classified as a heterogeneous mixture.

(c) Iodine Crystals

Iodine crystals consist of only iodine molecules arranged in a specific pattern, without any other substances. This makes them a pure substance, specifically, a chemical element.

(d) Sand

Sand is a mixture of various small particles such as minerals, rocks, and organic matter. As the composition and size of these particles can vary throughout, sand is considered a heterogeneous mixture.