Chemistry Exam Review

1. Solubility Rules (from Section 9.3 and Lecture Slides)

These rules help you determine whether an ionic compound is soluble (dissolves in water) or forms a precipitate.

Always Soluble

  • Group 1 cations (Li^+, Na^+, K^+, etc.)

  • Ammonium (NH_4^+)

  • Nitrates (NO_3^-)

  • Acetates (CH_3COO^-)

  • Perchlorates (ClO_4^-)

Usually Soluble

  • Chlorides, bromides, iodides (Cl^- , Br^- , I^-)

    • Except: Ag^+, Pb^{2+}, Hg_2^{2+}

  • Sulfates (SO_4^{2-})

    • Except: Ca^{2+}, Sr^{2+}, Ba^{2+}, Pb^{2+}

Insoluble Compounds

  • Carbonates (CO_3^{2-})

  • Phosphates (PO_4^{3-})

  • Sulfides (S^{2-})

  • Hydroxides (OH^-)

    • Except: Group 1 and Ba^{2+} are soluble.

2. Balancing Chemical Equations

Balancing ensures the same number of each atom appears on both sides of the equation.

Steps

  1. Write the unbalanced equation.

  2. Balance metals first.

  3. Balance nonmetals next.

  4. Save H and O for last.

  5. Add coefficients; never change subscripts.

  6. Check your work by counting atoms on both sides.

Tips

  • If polyatomic ions appear unchanged on both sides, balance them as whole units.

  • Coefficients must be the smallest whole-number ratio.

3. STP (Standard Temperature and Pressure)

  • Temperature: 0°C or 273 K

  • Pressure: 1 atm

  • 1 mole of any gas at STP occupies 22.4 L

Useful Formula

V = n(22.4\,L)
Where n = moles of gas.

4. Gay-Lussac's Law (Pressure–Temperature Law)

Describes the direct relationship between pressure and temperature (in Kelvin).

Formula

\frac{P1}{T1} = \frac{P2}{T2}

Rules

Temperature must be in Kelvin.

  • Pressure increases when temperature increases (if volume is constant).

5. Molarity (M)

Molarity measures how concentrated a solution is.

Formula

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

Dilutions

Use the dilution equation:
M1V1 = M2V2
Where:

  • M1 , V1 = initial concentration and volume

  • M2 , V2 = final concentration and volume

Molarity from Mass

  1. Convert mass o moles using molar mass.

  2. Convert volume to liters.

  3. Use (M = \frac{mol}{L}).

6. Limiting Reactant

The limiting reactant is the substance that is used up first and limits how much product can form.

Steps to Identify

  1. Convert each reactant to moles.

  2. Use the balanced equation to determine mole ratios.

  3. Calculate how much product each reactant could make.

  4. The smallest product amount indicates the limiting reactant.

Shortcut Method

  • Determine moles of each reactant.

  • Divide by its coefficient in the balanced equation.

  • The smallest result = limiting reactant.

7. Essential Practice Calculations

  • Converting between grams \leftrightarrow moles.

  • Gas volume \leftrightarrow moles at STP.

  • Using solubility rules to predict precipitates.

  • Applying Gay-Lussac's Law.

  • Doing dilution calculations for molarity.

  • Identifying limiting reactants and theoretical yield.

Success Tips

Write units everywhere—they guide the math.

  • Always check if temperature must be converted to Kelvin.
    For solutions, be careful distinguishing mL vs L.

  • Memorize the most common solubility exceptions.

  • When in doubt: convert everything to moles.