Matter And Mixtures | Grandinetti Group

Matter

For chemists, the fundamental building block of matter is the atom. An atom is the smallest unit of an element that still retains the element’s chemical properties. Although atoms can be further divided into subatomic particles (electrons, protons, and neutrons), it is at the atomic level that the first distinctive “chemical” characteristics appear. The periodic table catalogs these atoms, each with its unique traits.

States of Matter

Matter exists primarily in three states, each defined by the arrangement and movement of its particles:

• Solid: Possesses a definite shape and volume. The particles are tightly packed, giving solids their rigidity and resistance to shape changes.
• Liquid: Has a definite volume but adapts to the shape of its container. The particles are less tightly bound than in solids, allowing them to flow.
• Gas: Lacks both a definite shape and volume. Gas particles move freely and expand to fill any container.

Think About It: Can you identify examples of solids, liquids, and gases in everyday life? Consider what makes each unique. Hint: Look for common examples such as ice (solid), water (liquid), and air (gas).

Demo:

1. Cl2(g), Br2(l), I2(s)
2. Dip Br2(l) into liquid nitrogen and observe the formation of Br2(s)

Mixtures

A pure substance consists of only one type of atom or molecule. In contrast, much of the material around us is composed of mixtures – combinations of two or more pure substances. Common examples include air, wood, rocks, and soil. Mixtures can be classified into two types: homogeneous mixtures (where the components are evenly distributed) and heterogeneous mixtures (where the components remain distinct).

Homogeneous Mixtures

Homogeneous mixtures have components that are uniformly distributed at the atomic or molecular level. These mixtures are also known as solutions. Examples include:

Air is a gaseous solution composed of gases like N2, O2, H2O, and CO2. Although each gas is a pure substance by itself, their molecular-level mixing forms a homogeneous mixture.

Brass is a solid solution of copper and zinc. Here, the atoms are mixed so finely that the metals blend into a uniform material.

Beer is an example of a liquid solution, made up of water, ethanol (C2H5OH), and other substances. Notice that while ethanol is responsible for its intoxicating effects, beer does not have a single “beer molecule.”

Heterogeneous Mixtures

In heterogeneous mixtures, the components are not uniformly distributed on the atomic or molecular scale. This results in mixtures where the different substances remain visually distinct. For example, consider:

Salt and pepper, chocolate chip cookies, or a Twix™ candy bar

Each of these examples contains components that can be observed and separated without the need for special techniques.

Physical separation methods are techniques that exploit differences in physical properties (such as boiling point, solubility, or magnetism) without altering the chemical composition of the substances. Remember, regardless of the type, mixtures can be separated into their pure components using these physical methods, such as distillation or chromatography.

Demo:

1. Separate iron filings and sulfur using a magnet.
2. Use chromatography to separate grape soda into its orange and blue components.

Physical Change

A physical change alters the form or state of a substance without changing its chemical composition. A common example is the boiling of water, which involves a transition from the liquid to the gaseous state:

H2O(l) → H2O(g)

In this process, (l) denotes the liquid state and (g) the gaseous state. Although the form changes, the molecular structure of H2O remains the same.

Think About It: What other everyday processes involve a physical change?

Demo:

1. Observe the sublimation of dry ice: CO2(s) → CO2(g).
2. Demonstrate the evaporation of hydrogen peroxide: H2O2(l) → H2O2(g).

Chemical Change

A chemical change occurs when the molecules of a substance are rearranged, resulting in the formation of one or more new substances with different chemical properties. An example is the combustion of ethanol, which can be represented by:

Demo:

1. C2H5OH + 2 O2(g) → 2 CO2(g) + 3 H2O(g)

In a chemical change, new products are formed. For example, in an incandescent light bulb, tungsten is shielded from oxygen; if oxygen were present, tungsten would oxidize to form tungsten oxide:

2W + 3O2 → 2WO3

This reaction damages the tungsten filament, reducing its ability to conduct electricity and produce light. Chemical changes, such as these, illustrate how atoms can rearrange to form entirely new substances.

Reflect: Can you list other everyday examples where chemical changes occur? How do these changes differ from physical changes? Hint: Consider processes like rusting, burning, or cooking, where new substances are formed.

Demo:

1. Show a light bulb with a drilled hole to illustrate how oxygen causes tungsten to oxidize and eventually burn out the filament.

Homework from Chemisty, The Central Science, 10th Ed.

1.1, 1.2, 1.9, 1.19, 1.21