CHEM 110 Lab Exam 1 Study Guide: Matter, Measurement, and Chemical Composition

Matter and Its Classification

Heterogeneous and Homogeneous Mixtures

Matter can be classified based on its composition and uniformity. Understanding the differences between mixtures and pure substances is fundamental in chemistry.

• Heterogeneous Mixture: A mixture in which the composition is not uniform throughout. Different components can often be seen and separated physically. Example: Salad, sand and iron filings.

• Homogeneous Mixture: A mixture with a uniform composition throughout; also called a solution. Example: Saltwater, air.

Pure Substances

Pure substances have a fixed composition and distinct properties. They can be elements or compounds.

• Element: A substance that cannot be broken down into simpler substances by chemical means. Consists of only one type of atom. Example: Oxygen (O2), Gold (Au).

• Compound: A substance composed of two or more elements chemically combined in a fixed ratio. Example: Water (H2O), Carbon dioxide (CO2).

Atoms, Elements, and Compounds

Atoms and Elements

Atoms are the basic units of matter, and elements are substances made up of only one kind of atom.

• Atomic Element: An element that exists in nature as single atoms. Example: Helium (He), Neon (Ne).

• Molecular Element: An element that exists as molecules, typically two or more atoms bonded together. Example: Oxygen (O2), Nitrogen (N2).

Molecular Compounds

Molecular compounds are composed of molecules formed by two or more nonmetal atoms bonded together.

• Example: Carbon dioxide (CO2), Water (H2O).

Properties and Changes of Matter

Physical and Chemical Properties

Properties of matter can be classified as physical or chemical.

• Physical Properties: Characteristics that can be observed or measured without changing the substance's identity. Examples: Color, melting point, density.

• Chemical Properties: Characteristics that describe a substance's ability to change into different substances. Examples: Flammability, reactivity with acid.

Physical and Chemical Changes

Changes in matter can be physical or chemical.

• Physical Change: A change that does not alter the chemical composition of a substance. Example: Melting ice, dissolving sugar in water.

• Chemical Change: A change that results in the formation of one or more new substances. Example: Rusting of iron, burning of wood.

Ions: Cations and Anions

Definition of Ions

Ions are atoms or molecules that have gained or lost electrons, resulting in a net charge.

• Cation: A positively charged ion, formed when an atom loses one or more electrons. Example: Sodium ion (Na+).

• Anion: A negatively charged ion, formed when an atom gains one or more electrons. Example: Chloride ion (Cl-).

Measurement and Problem Solving

Significant Figures

Significant figures reflect the precision of a measured or calculated quantity.

• All nonzero digits are significant.

• Zeros between nonzero digits are significant.

• Leading zeros are not significant.

• Trailing zeros are significant only if there is a decimal point.

• Example: 0.00450 has three significant figures.

Density

Density is a physical property that relates the mass of a substance to its volume.

• Formula:

$\text{Density} = \frac{\text{Mass}}{\text{Volume}}$

• Units: Commonly expressed in grams per cubic centimeter (g/cm3) or grams per milliliter (g/mL).

• Example: If a block has a mass of 10 g and a volume of 2 mL, its density is 5 g/mL.

Dimensional Analysis (Unit Conversion)

Dimensional analysis is a method for converting one unit to another using conversion factors.

• Steps:

  1. Identify the starting and desired units.

  2. Set up conversion factors so units cancel appropriately.

  3. Multiply through to obtain the answer in the desired units.

• Example: Convert 5.0 cm to meters:

  • Conversion factor: 1 m = 100 cm

  • Calculation: $5.0\ \text{cm} \times \frac{1\ \text{m}}{100\ \text{cm}} = 0.050\ \text{m}$

Summary Table: Classification of Matter

Type of Matter	Description	Example
Element	Pure substance, cannot be broken down by chemical means	Oxygen (O2), Gold (Au)
Compound	Pure substance, composed of two or more elements chemically combined	Water (H2O), Carbon dioxide (CO2)
Homogeneous Mixture	Uniform composition throughout	Saltwater, air
Heterogeneous Mixture	Non-uniform composition, components visible	Salad, sand and iron filings

Additional info: Academic context and examples have been added to clarify and expand upon the brief list of topics provided in the original study guide.