Problem 13 - Chemistry: The Central Science

Question

Classify each of the following as a pure substance or a mixture. If a mixture, indicate whether it is homogeneous or heterogeneous: (a) rice pudding, (b) seawater, (c) magnesium, (d) crushed ice.

Step-by-Step Solution

Answer

(a) Rice pudding is a heterogeneous mixture. (b) Seawater is a homogeneous mixture. (c) Magnesium is a pure substance. (d) Crushed ice is a pure substance.

Step 1: Identifying Pure Substances or Mixtures

A pure substance is a material that consists of only one type of element or compound. A mixture contains two or more different substances that are physically combined but not chemically bonded together. Mixtures can be further classified into homogeneous or heterogeneous. Homogeneous mixtures have a uniform composition and phase throughout, whereas heterogeneous mixtures have regions with different compositions and phases. Now, let's classify each given example:

Step 2: (a) Rice Pudding

Rice pudding consists of rice, milk, sugar, and other ingredients mixed together in various proportions. Since these components are physically combined and not chemically bonded, it is a mixture. Additionally, the different components in rice pudding can be seen and separated by simple mechanical methods, making it a heterogeneous mixture.

Step 3: (b) Seawater

Seawater is a mixture of water, dissolved salts, and other minerals. Although the composition of seawater varies from one location to another, it appears the same throughout a particular sample and cannot be separated by simple mechanical methods. It is, therefore, a homogeneous mixture.

Step 4: (c) Magnesium

Magnesium is a chemical element with the symbol Mg. It is a metal, and when found in pure form, it consists of only one type of atom. Therefore, magnesium is a pure substance.

Step 5: (d) Crushed Ice

Crushed ice is made up of small pieces of ice. As the ice is in solid-state, it is essentially water molecules tightly packed together in a crystal lattice structure. Since the crushed ice only consists of water without any other substances mixed in, it is a pure substance. To summarize, rice pudding is a heterogeneous mixture, seawater is a homogeneous mixture, magnesium is a pure substance, and crushed ice is a pure substance.