GOB Chemistry Midterm 2 Study Guide: Key Concepts and Applications

Chapter 7: Chemical Quantities and Reactions

Understanding Chemical Quantities

This topic covers the conversion between different units in chemical calculations, including atoms, moles, molecules, grams, and products/reactants. Mastery of these conversions is essential for quantitative chemical analysis.

• Mole Concept: The mole is a fundamental unit in chemistry representing $6.022 \times 10^{23}$ entities (Avogadro's number).

• Conversions: Be able to convert between atoms, moles, molecules, grams, and products/reactants using molar mass and Avogadro's number.

• Molar Mass: The mass of one mole of a substance, typically expressed in g/mol.

• Chemical Equations: Identify and write chemical reaction equations, including the five main types:

  • Combination (Synthesis)

  • Decomposition

  • Single Displacement

  • Double Displacement

  • Combustion

• Catalyst: A substance that increases the rate of a chemical reaction without being consumed.

Example: Calculate the number of moles in 18 g of water ($H_2O$). Molar mass of $H_2O = 18$ g/mol, so $\frac{18\,g}{18\,g/mol} = 1$ mole.

Chapter 8: Gases

Pressure Units and Gas Laws

This section focuses on the conversion between different pressure units and the application of gas laws to solve problems involving gases.

• Pressure Units: Common units include mmHg, atm, torr, Pa, and kPa.

• Combined Gas Law: Relates pressure, volume, and temperature: $\frac{P_1V_1}{T_1} = \frac{P_2V_2}{T_2}$

• Law of Partial Pressures (Dalton's Law): The total pressure of a mixture of gases is the sum of the partial pressures of each gas: $P_{total} = P_1 + P_2 + P_3 + \ldots$

• Avogadro's Law: Equal volumes of gases at the same temperature and pressure contain equal numbers of molecules: $\frac{V_1}{n_1} = \frac{V_2}{n_2}$

Example: Convert 1 atm to mmHg. $1\,atm = 760\,mmHg$

Chapter 9: Solutions

Concentration and Solution Preparation

This topic covers calculations involving solution concentration, including molarity, percent by mass, and volume. It also addresses the identification of electrolytes and non-electrolytes.

• Molarity ($M$): $M = \frac{\text{moles of solute}}{\text{liters of solution}}$

• Percent by Mass: $\%\,\text{mass} = \frac{\text{mass of solute}}{\text{mass of solution}} \times 100$

• Electrolytes vs. Non-electrolytes: Electrolytes conduct electricity in solution; non-electrolytes do not.

• Dilution Calculations: Use $M_1V_1 = M_2V_2$ to calculate dilutions.

Example: How much $NaCl$ is needed to prepare 500 mL of a 0.2 M solution? $\text{Moles} = 0.2\,mol/L \times 0.5\,L = 0.1\,mol$

Chapter 10: Acids, Bases, and Equilibrium

Acid-Base Identification and Calculations

This section focuses on identifying strong and weak acids/bases, calculating pH and pOH, and understanding acid-base reactions and conjugate pairs.

• Strong vs. Weak Acids/Bases: Strong acids/bases dissociate completely; weak acids/bases do not.

• pH and pOH Calculations:

  • $pH = -\log[H^+]$

  • $pOH = -\log[OH^-]$

  • $pH + pOH = 14$

• Acid-Base Reactions: Identify reactants and products, and determine conjugate acid-base pairs.

• Titration: Use titration data to calculate unknown concentrations: $M_1V_1 = M_2V_2$

Example: Calculate the pH of a solution with $[H^+] = 1 \times 10^{-3}$ M. $pH = -\log(1 \times 10^{-3}) = 3$

Chapter 11: Introduction to Organic Chemistry: Hydrocarbons

Hydrocarbon Structure and Nomenclature

This topic introduces the structure and naming of alkanes, alkenes, and alkynes, including the use of IUPAC rules and condensed/expanded structures.

• Alkanes: Saturated hydrocarbons with single bonds.

• Alkenes: Unsaturated hydrocarbons with at least one double bond.

• Alkynes: Unsaturated hydrocarbons with at least one triple bond.

• IUPAC Naming: Systematic method for naming organic compounds based on structure.

• Condensed vs. Expanded Structures: Condensed shows connectivity; expanded shows all bonds.

Example: Name the compound $CH_3CH_2CH_3$ (propane).

Chapter 12: Alcohols, Thiols, Ethers, Aldehydes, and Ketones

Functional Groups and Reactions

This section covers the identification and structure of key organic functional groups and their reactions, including oxidation and reduction.

• Alcohols: Contain the -OH group.

• Thiols: Contain the -SH group.

• Ethers: Contain an oxygen atom between two carbon groups.

• Aldehydes: Contain a carbonyl group ($-CHO$) at the end of a carbon chain.

• Ketones: Contain a carbonyl group ($C=O$) within the carbon chain.

• Oxidation/Reduction Reactions: Alcohols can be oxidized to aldehydes/ketones; aldehydes can be further oxidized to acids.

• Tollens' Test: Used to identify aldehydes (silver mirror test).

Example: Oxidation of ethanol ($CH_3CH_2OH$) produces acetaldehyde ($CH_3CHO$).