General Chemistry 115: Exam 1B Study Notes

General Chemistry Fundamentals

Unit Conversions and Useful Equations

Understanding unit conversions and basic equations is essential in general chemistry for solving quantitative problems.

• Density (D): The mass per unit volume of a substance. Formula: $D = \frac{\text{mass}}{\text{volume}}$

• Volume of a Sphere: Formula: $V = \frac{4}{3} \pi r^3$, where $\pi = 3.141592$

• Common Conversion Factors:

  • 1 mile = 5280 feet

  • 1 foot = 12 inches

  • 1 inch = 2.54 cm

  • 1 liter = 1.05669 quarts

  • 1 mile = 1.60934 km

  • 1000 mg = 1 g

  • 1 mL = 1 cm3

Chemical Nomenclature and Formulas

Elements, Ions, and Compounds

Chemical nomenclature is the system for naming chemical substances. It is important to know both the names and symbols/formulas for elements, ions, and compounds.

• Element Symbols: Each element is represented by a one- or two-letter symbol (e.g., Na for sodium, S for sulfur).

• Common Polyatomic Ions:

  • Hydrogen phosphite: $\text{HPO}_3^{2-}$

  • Acetate: $\text{C}_2\text{H}_3\text{O}_2^-$ or $\text{CH}_3\text{COO}^-$

  • Copper(II) perchlorate: $\text{Cu(ClO}_4)_2$

  • Strontium oxide: $\text{SrO}$

  • Calcium nitrite: $\text{Ca(NO}_2)_2$

• Acids:

  • Hydrochloric acid: $\text{HCl}$

  • Hydrobromic acid (aqueous): $\text{HBr(aq)}$

Example: Name the compound with the formula $\text{Na}_2\text{SO}_4$: Sodium sulfate.

Significant Figures

Counting Significant Figures

Significant figures (sig figs) are the digits in a measurement that are known with certainty plus one digit that is estimated. They are important for expressing the precision of measurements and calculations.

• Rules for Counting Significant Figures:

  • 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.

• Examples:

  • 1.057 × 104 has 4 significant figures.

  • 0.00230122 has 6 significant figures.

  • 13.3 × 104 has 3 significant figures.

  • 0.00048 has 2 significant figures.

  • 499.100 has 6 significant figures.

Chemical Formulas

Writing Formulas for Compounds

It is important to be able to write the correct chemical formula for a compound given its name, and vice versa.

• Tetraphosphorous decoxide: $\text{P}_4\text{O}_{10}$

• Potassium sulfate: $\text{K}_2\text{SO}_4$

• Barium chlorate: $\text{Ba(ClO}_3)_2$

• Sulfur dioxide: $\text{SO}_2$

• Magnesium chloride: $\text{MgCl}_2$

Example: The formula for magnesium chloride is $\text{MgCl}_2$.

Solution Concentration

Molarity Calculations

Molarity (M) is a measure of the concentration of a solute in a solution, defined as moles of solute per liter of solution.

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

• Steps to Calculate Molarity:

  1. Convert grams of solute to moles using the molar mass.

  2. Convert the volume of solution to liters.

  3. Divide moles of solute by liters of solution.

• Example: Calculate the molarity of a solution in which 26.0 grams of $\text{BaCl}_2$ (molar mass = 208.2 g/mol) are dissolved in enough water to make 450.0 mL of solution.

  • Moles of $\text{BaCl}_2$: $\frac{26.0\ \text{g}}{208.2\ \text{g/mol}} = 0.125\ \text{mol}$

  • Volume in liters: $450.0\ \text{mL} = 0.4500\ \text{L}$

  • Molarity: $M = \frac{0.125}{0.4500} = 0.278\ \text{M}$

Summary Table: Common Polyatomic Ions and Compounds

Name	Formula
Sodium sulfate	Na2SO4
Hydrogen phosphite	HPO32-
Acetate	C2H3O2-
Copper(II) perchlorate	Cu(ClO4)2
Strontium oxide	SrO
Calcium nitrite	Ca(NO2)2

Additional info: These notes are based on the content and structure of a General Chemistry 115 exam, focusing on nomenclature, significant figures, unit conversions, and solution concentration calculations.