Problem 101 - Chemistry Matter and Change

Question

Identify each of the following as an element, a compound, a homogeneous mixture, or a heterogeneous mixture. (Chapter 3) . $$ \begin{array}{ll}{\text { a. air }} & {\text { d. ammonia }} \\ {\text { b. blood }} & {\text { e. mustard }} \\ {\text { c. antimony }} & {\text { f. water }}\end{array} $$

Step-by-Step Solution

Answer

a. Air is a homogeneous mixture. b. Blood is a heterogeneous mixture. c. Antimony is an element. d. Ammonia is a compound. e. Mustard is a heterogeneous mixture. f. Water is a compound.

Step 1: Identifying air

Air is a mixture of different gases, including nitrogen, oxygen, and trace amounts of other gases. These gases are evenly dispersed throughout the mixture, so it is considered a homogeneous mixture.

Step 2: Identifying blood

Blood is a complex mixture of plasma, red blood cells, white blood cells, and platelets. The components of blood are not uniformly distributed throughout the mixture, so it is classified as a heterogeneous mixture.

Step 3: Identifying antimony

Antimony is a chemical element with the symbol Sb and atomic number 51. It is a pure substance made up of only one type of atom, so it is classified as an element.

Step 4: Identifying ammonia

Ammonia is a compound with the chemical formula NH3. It consists of one nitrogen atom and three hydrogen atoms chemically bonded together, so it is classified as a compound.

Step 5: Identifying mustard

Mustard is a condiment made from various ingredients, such as mustard seeds, water, vinegar, and additional spices. The composition of mustard is not uniform throughout, which makes it a heterogeneous mixture.

Step 6: Identifying water

Water is a compound with the chemical formula H2O. It consists of two hydrogen atoms bonded to one oxygen atom, so it is classified as a compound.

Key Concepts

Homogeneous Mixture

When we refer to a homogeneous mixture, we are talking about a mixture in which its components are evenly distributed throughout the substance. An easy way to remember this is to think of the word 'homo' which means 'the same'; everything in this type of mixture is uniform. A classic example, as mentioned in the exercise, is air. Even though air is composed of various gases like nitrogen, oxygen, and small amounts of other gases, each breath you take will contain these gases in roughly the same proportion. Other examples of homogeneous mixtures include saltwater, vinegar, and steel.

To improve understanding of this concept, consider making a cup of coffee with sugar. Once you stir the sugar into the coffee, you can't see distinct sugar particles anymore. The sugar dissolves evenly, making it a homogeneous mixture.

Heterogeneous Mixture

Unlike homogeneous mixtures, the components in a heterogeneous mixture are not uniformly spread out. This type of mixture contains visibly different substances or phases. Think of 'hetero' which means 'different'. In our exercise, blood is given as an example. When looking at blood under a microscope, you can see red cells, white cells, plasma, and platelets each occupying different spaces and not evenly mixed. Other commonplace examples include a bowl of cereal with milk, a rock with various minerals, and even the condiment mustard, which contains different ingredients such as seeds and spices that remain distinct within the mixture.

For students to grasp this concept more solidly, a hands-on activity can be helpful; mixing oil and water can showcase how the two liquids do not blend together into a uniform mixture, quite visibly representing a heterogeneous mixture.

Chemical Element

A chemical element is a pure substance that cannot be broken down into simpler substances by chemical means. Each element is made up of one kind of atom and is represented on the periodic table. The exercise brings up antimony as an element, which is composed entirely of atoms with the atomic number 51. Other familiar elements include hydrogen, oxygen, gold, and iron. Elements are the building blocks for all other substances.

To clarify this concept for students, discussing the unique properties that define an element, such as boiling point, melting point, and reactivity, can be useful. Furthermore, showing real-life examples like a piece of copper wire or an aluminum can illustrate what pure elements might look like in everyday life.

Chemical Compound

A chemical compound is a substance formed when two or more different elements combine in fixed ratios and are held together by chemical bonds. The example given in the exercise is water (H₂O) made up of two hydrogen atoms bonded to one oxygen atom. Another instance is ammonia (NH₃), which consists of nitrogen and hydrogen in a 1:3 ratio. Compounds have different properties from their component elements. For example, sodium is a reactive metal, and chlorine is a poisonous gas, but when they combine to form sodium chloride (NaCl), the result is table salt, which is safe to consume.

To aid student comprehension, discussing the process of how elements bond together can be enlightening, such as explaining that water is formed from hydrogen and oxygen through a process called chemical synthesis. Explaining this provides a clearer picture of how different atoms come together to create compounds with unique properties.