General Chemistry I: Practice Exam 1 Study Notes

Ch.1 - Matter, Measurement & Problem Solving

Classification of Matter

Matter can be classified as elements, compounds, or mixtures based on its composition and properties.

• Element: A pure substance consisting of only one type of atom (e.g., Ca for calcium).

• Compound: A substance formed from two or more elements chemically bonded in fixed proportions (e.g., NaCl for sodium chloride).

• Mixture: A physical combination of two or more substances where each retains its own properties (e.g., air, saltwater).

Example: Classify the following: CO2 (compound), Ca (element), Al (element), P4 (element), Ammonium phosphate (compound), Sodium chloride (compound).

Chemical vs. Physical Changes

Changes in matter are classified as either physical or chemical:

• Physical Change: Alters the form or appearance of matter but does not change its composition (e.g., melting ice, boiling water).

• Chemical Change: Results in the formation of one or more new substances with different properties (e.g., burning wood, rusting iron).

Example: Boiling water (physical), burning wood (chemical), making lemonade (physical), baking a cake (chemical).

Unit Conversions

Unit conversions are essential for solving chemistry problems. Use conversion factors to relate different units.

• Example: To convert gallons to milliliters, use the relationships: 1 gal = 3.79 L, 1 L = 1000 mL.

Formula:

$\text{Volume in mL} = \text{Volume in gal} \times 3.79 \frac{\text{L}}{\text{gal}} \times 1000 \frac{\text{mL}}{\text{L}}$

Temperature Conversions

Temperature can be measured in Celsius (°C) or Kelvin (K). The conversion is:

$K = ^\circ C + 273.15$

Example: Convert 98.6°C to K: $98.6 + 273.15 = 371.75$ K

Density Calculations

Density relates the mass and volume of a substance:

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

To find mass: $\text{Mass} = \text{Density} \times \text{Volume}$

Example: Methanol has a density of 0.7918 g/mL. The mass of 18.0 mL is $0.7918 \times 18.0 = 14.2524$ g.

Comparing Densities

To determine which block has a greater mass, use the density and volume:

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

Compare the calculated masses for each block.

Ch.2 - Atoms & Elements

Subatomic Particles

Atoms are composed of protons, neutrons, and electrons:

• Proton: Charge = +1, found in the nucleus

• Neutron: Charge = 0, found in the nucleus

• Electron: Charge = -1, found in the electron cloud surrounding the nucleus

Atomic Structure

The number of protons, neutrons, and electrons in an atom can be determined from its atomic number and mass number.

• Atomic Number (Z): Number of protons

• Mass Number (A): Number of protons + neutrons

• Number of Electrons: Equal to protons in a neutral atom

Example: For 12C: 6 protons, 6 neutrons, 6 electrons

Isotopes

Isotopes are atoms of the same element with different numbers of neutrons.

Ch.3 - Molecules and Compounds

Molar Mass

The molar mass is the mass of one mole of a substance, expressed in g/mol.

• For elements: Use the atomic mass from the periodic table.

• For compounds: Sum the atomic masses of all atoms in the formula.

Example: Molar mass of H2O = 2(1.01) + 16.00 = 18.02 g/mol

Counting Atoms and Molecules

Avogadro's number ($6.022 \times 10^{23}$) is used to convert between moles and number of particles.

$\text{Number of particles} = \text{moles} \times 6.022 \times 10^{23}$

Example: Number of Li atoms in 0.524 mol = $0.524 \times 6.022 \times 10^{23}$

Types of Compounds: Ionic vs. Covalent

• Ionic Compounds: Formed from metals and nonmetals; consist of ions held together by electrostatic forces (e.g., NaCl).

• Covalent Compounds: Formed from nonmetals; atoms share electrons (e.g., CH4).

Electron Gain/Loss and Full Shells

Atoms tend to gain or lose electrons to achieve a full valence shell (octet rule).

• Metals tend to lose electrons (form cations).

• Nonmetals tend to gain electrons (form anions).

BONUS: Mathematical Operations and Functions

Significant Figures

When performing calculations, report answers with the correct number of significant figures based on the data provided.

• For multiplication/division: Use the least number of significant figures from the input values.

• For addition/subtraction: Use the least number of decimal places from the input values.

Table: Comparison of Subatomic Particles

Particle	Charge	Location
Proton	+1	Nucleus
Neutron	0	Nucleus
Electron	-1	Electron cloud

Additional info:

• Some questions reference homework or recitation problems, which are not included in the file.

• Students are reminded to show all work and use correct significant figures.