General Chemistry Study Guide: Solutions, Acids & Bases, Equilibrium, Nuclear Chemistry, and Redox

Chapter 13: Solutions

Mass Percent and Solution Concentration

Solutions are homogeneous mixtures composed of a solute dissolved in a solvent. The concentration of a solution can be expressed in several ways, including mass percent, molarity, and molality.

• Mass Percent (%): The mass percent of a component in a solution is calculated as:

$\text{Mass percent} = \frac{\text{mass of solute}}{\text{mass of solution}} \times 100$

• Example: If you dissolve 5.0 g of NaCl in 95.0 g of water, the mass percent of NaCl is:

$\text{Mass percent NaCl} = \frac{5.0}{5.0 + 95.0} \times 100 = 5\%$

• Molarity (M): Molarity is the number of moles of solute per liter of solution.

$M = \frac{\text{moles of solute}}{\text{liters of solution}}$

• Example: To prepare 250 mL of 0.50 M NaCl solution, calculate the grams of NaCl needed:

$\text{Moles NaCl} = 0.50 \times 0.250 = 0.125$ mol $\text{Mass NaCl} = 0.125 \times 58.44 = 7.305$ g

• Solution Dilution: To dilute a solution, use the equation:

$M_1V_1 = M_2V_2$

• Example: To make 100 mL of 0.1 M HCl from 1.0 M HCl:

$V_1 = \frac{M_2V_2}{M_1} = \frac{0.1 \times 100}{1.0} = 10$ mL

Chapter 14: Acids and Bases

Acid and Base Strength, pH, and pOH

Acids and bases are classified by their ability to donate or accept protons (Brønsted-Lowry theory). The concentration of hydrogen ions in solution determines acidity.

• pH: The pH of a solution is a measure of its hydrogen ion concentration.

$pH = -\log[H^+]$

• pOH: The pOH is related to the hydroxide ion concentration.

$pOH = -\log[OH^-]$

• Relationship:

$pH + pOH = 14$

• Acidic, Basic, and Neutral Solutions:

pH Range	Solution Type
0 < pH < 7	Acidic
pH = 7	Neutral
7 < pH < 14	Basic

• Calculating Concentrations: If you know the pH, you can find [H+]:

$[H^+] = 10^{-pH}$

• Example: If pH = 3, $[H^+] = 10^{-3} = 0.001$ M

Chapter 15: Chemical Equilibrium

Equilibrium Expressions and Le Châtelier's Principle

Chemical equilibrium occurs when the rates of the forward and reverse reactions are equal, and the concentrations of reactants and products remain constant.

• Equilibrium Constant (K): For a reaction $aA + bB \rightleftharpoons cC + dD$:

$K = \frac{[C]^c[D]^d}{[A]^a[B]^b}$

• Le Châtelier's Principle: If a system at equilibrium is disturbed, it will shift to counteract the disturbance.

• Factors Affecting Equilibrium:

  • Adding/removing reactants or products

  • Changing pressure (for gases)

  • Changing temperature

• Example: Increasing the concentration of a reactant shifts equilibrium to the right (toward products).

Chapter 17: Nuclear Chemistry

Types of Radiation and Nuclear Reactions

Nuclear chemistry studies changes in atomic nuclei, including radioactive decay and nuclear reactions.

• Types of Radiation:

  • Alpha (α): Helium nucleus, $^4_2He$

  • Beta (β): Electron, $^0_{-1}e$

  • Gamma (γ): High-energy photon

  • Positron: $^0_{+1}e$

• Balancing Nuclear Equations: The sum of atomic and mass numbers must be equal on both sides.

• Half-life ($t_{1/2}$): The time required for half of a radioactive sample to decay.

$N = N_0 \left(\frac{1}{2}\right)^{\frac{t}{t_{1/2}}}$

• Example: If 12.5% of a sample remains after 3 half-lives, then $\left(\frac{1}{2}\right)^3 = \frac{1}{8} = 12.5\%$

Chapter 16: Oxidation and Reduction (Redox)

Redox Reactions and Balancing

Oxidation-reduction (redox) reactions involve the transfer of electrons between species. Oxidation is the loss of electrons, and reduction is the gain of electrons.

• Oxidation Number: A value assigned to an atom to indicate its degree of oxidation or reduction.

• Identifying Redox Reactions: The substance that loses electrons is oxidized (reducing agent), and the substance that gains electrons is reduced (oxidizing agent).

• Example: In the reaction $Mg + CuSO_4 \rightarrow MgSO_4 + Cu$:

  • Mg is oxidized (loses electrons)

  • Cu2+ is reduced (gains electrons)

• Balancing Redox Reactions: Use the half-reaction method, balancing atoms and charges.

$\text{Example half-reaction: } Fe^{2+} \rightarrow Fe^{3+} + e^-$

Additional info: This guide expands on the provided exam review questions by supplying definitions, formulas, and examples for each topic, ensuring a comprehensive overview suitable for exam preparation.