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. (d) Sand is a heterogeneous mixture.

Step-by-step solution

(a) Air

Air is a mixture of various gases like nitrogen, oxygen, carbon dioxide, and other trace gases. These gases are uniformly distributed throughout the air, making it a homogeneous mixture.

(b) Tomato juice

Tomato juice is a mixture of various components like water, tomato particles, vitamins, and minerals. These components do not have a uniform distribution due to the presence of tomato particles, making tomato juice a heterogeneous mixture.

(c) Iodine crystals

Iodine crystals consist of iodine molecules (I2) which are chemically bonded. It has a constant composition and cannot be separated into simpler substances by physical means. Therefore, iodine crystals are a pure substance.

(d) Sand

Sand contains tiny particles of various minerals and rocks, such as quartz, feldspar, and mica. Each particle retains its own unique properties, so it is a mixture. Since these different particles are not uniformly distributed, sand is a heterogeneous mixture.