Problem 68 - Introductory Chemistry Atoms First

Question

Classify each of the following as elemental substance, compound, or mixture: (a) Milk (b) Chocolate cake (c) Clean snow, \(\mathrm{H}_{2} \mathrm{O}(s)\) (d) The simple sugar fructose, \(\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}\) (e) The mercury, \(\mathrm{Hg}\), in a thermometer

Step-by-Step Solution

Answer

(a) Milk: mixture (b) Chocolate cake: mixture (c) Clean snow, \(\mathrm{H}_{2} \mathrm{O}(s)\): compound (d) The simple sugar fructose, \(\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}\): compound (e) The mercury, \(\mathrm{Hg}\), in a thermometer: elemental substance

Step 1: Milk

Milk is composed of various substances, such as water, fat, proteins, lactose, vitamins, and minerals. These components are not chemically bonded together and can be separated by physical methods. Therefore, milk can be classified as a mixture. (b)

Step 2: Chocolate Cake

A chocolate cake is made up of several ingredients like flour, sugar, cocoa powder, baking soda, and others, as well as air trapped in the batter during mixing, which later forms the cake's porous texture. These ingredients aren't chemically bonded together and can be separated by physical methods. Hence, chocolate cake is a mixture. (c)

Step 3: Clean snow, \(\mathrm{H}_{2} \mathrm{O}(s)\)

Clean snow is simply solid water (ice). Water is formed by two hydrogen atoms and one oxygen atom chemically bonded in a fixed proportion. Therefore, clean snow as \(\mathrm{H}_{2} \mathrm{O}(s)\) can be classified as a compound. (d)

Step 4: The simple sugar fructose, \(\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}\)

Fructose is composed of six carbon atoms, twelve hydrogen atoms, and six oxygen atoms chemically bonded together in a fixed proportion. As a result, fructose can be classified as a compound. (e)

Step 5: The mercury, \(\mathrm{Hg}\), in a thermometer

Mercury (Hg) is an element. In a thermometer, it consists of mercury atoms only and not any other substance. As such, the mercury in a thermometer can be classified as an elemental substance.

Key Concepts

Understanding Mixtures

Mixtures are fascinating because they involve combining different substances without actually changing their individual properties. Imagine mixing sand and salt. You can see and separate each component if needed. Indeed, in a mixture, components are not bonded chemically.

Here's what makes mixtures unique:

• They have variable compositions. For example, a glass of milk could have slightly different amounts of fat or sugar compared to another glass.
• You can usually separate them by physical means like filtration or decantation.
• Common examples include milk and chocolate cake, both containing various ingredients mixed together.

By understanding the nature of mixtures, we can better grasp how various everyday substances are composed and interact.

Exploring Compounds

Compounds are substances formed when two or more elements bond chemically in fixed proportions. Unlike mixtures, you cannot easily separate the components in a compound.

Characteristics of compounds include:

• They have consistent and reproducible properties.
• You need chemical reactions to break them down into simpler substances.
• Clean snow (water) and fructose are perfect examples, where water is composed of hydrogen and oxygen, and fructose consists of carbon, hydrogen, and oxygen.

By understanding compounds, we recognize the meticulous manner in which elements combine to form unique substances with specific properties.

Identifying Elemental Substances

Elemental substances are made of only one type of atom, earning them the title of pure substances. They are the building blocks of all other materials.

Important aspects of elemental substances include:

• They cannot be broken down into anything simpler by chemical means.
• Each element is unique in its structure and properties, like how mercury (Hg) is a liquid metal at room temperature.
• Elements are denoted by symbols in the periodic table, making it easy to understand their properties and behavior.

Learning about elemental substances helps us appreciate the fundamental components that make up the world and our everyday materials.

Basics of Chemical Bonding

Chemical bonding is the process that holds atoms together within a compound. Bonds form because atoms seek stable configurations, often achieving this by sharing or transferring electrons.

Key points about chemical bonding include:

• There are different types of bonds, such as ionic and covalent, each with unique characteristics and strength.
• Chemical bonds dictate the structure, stability, and reactivity of compounds.
• The arrangement and bond type directly influence the properties of compounds, evidenced in compounds like water and fructose.

Understanding chemical bonding is crucial as it explains how complex molecules and structures emerge from simpler atoms, playing a critical role in chemistry and our understanding of materials.