AP CHEM stuff to memorize

VSEPR not included. Some rules + equations + concepts

Significant figure rules

1. All non-zero digits are significant. In the measurement 4.27 g, there are three significant figures: 4, 2, and 7.

2. Zeros between non-zero digits are significant. Example: in 505 mL, there are three significant figures.

3. Leading zeros (zeros to the left of the first non-zero digit) are not significant. In 0.052 kg, the significant figures are 5 and 2.

4. Trailing zeros in a decimal number are significant. In 3.400 m, there are four significant figures. 

5. Trailing zeros in an integer are significant if they are followed by a decimal. In 1000. mL, there are four significant figures.

Solubility rules

1. Salts containing Group I elements are soluble (Li⁺, Na⁺, K⁺, Cs⁺, Rb⁺). Salts containing the ammonium ion (NH⁺) are also soluble. There are exceptions but they’re rare.

2. Salts containing nitrate ion (NO^-) are generally soluble.

3. Salts containing Cl^-, Br^-, I^- are generally soluble, except halide salts of Ag⁺, Pb²⁺, and (Hg₂)²⁺.

4. Most silver salts are insoluble except AgNO₂ and Ag(C₂H₂O₂).

5. Most sulfate salts are soluble except BaSO₄, PbSO₄, Ag₂SO₄ and SrSO₄.

6. Most hydroxide salts are only slightly soluble. Hydroxide salts of Group I elements (Ex. LiOH) are soluble. Hydroxide salts of Group II elements (CaOH, SrOH, and BaOH) are slightly soluble. Hydroxide salts of transition metals (Ex. Fe(OH)₃) and Al³⁺are insoluble.

7. Most sulfides of transition metals (Ex. CdS, FeS, ZnS) are highly insoluble.

8. Carbonates are frequently insoluble. Group II carbonates (Ca, Sr, and Ba) are insoluble. Some other insoluble carbonates include FeCO₃ and PbCO₃.

9. Chromates (CrO₄^2-) are frequently insoluble.

10. Phosphates (PO₄^3-) are frequently insoluble.

11. Fluorides are frequently insoluble.

Oxidation number rules

1. The oxidation number of a free, neutral element is zero.

2. The oxidation number of a monoatomic ion is equal to the charge of the ion.

3. The oxidation number of Group IA elements (the first column) is always +1.

4. The oxidation number of Group IIA elements (the second column) is always +2.

5. Oxidation number of H is +1 for bonds w/ nonmetals but -1 for bonds w/ metals. (metalloids are considered nonmetals in this case)

6. Oxidation number of O is typically -2, but is -1 in H₂O₂.

7. Oxidation number of F is always -1.

Effective nuclear charge

# protons - # core electrons

Coulomb’s law

F = Kq₁q₂/R². The core of this equation: larger radius → less attractive force, higher charge → more attractive force

Formal charge

# valence e^- - # (lone electrons + ½ shared electrons (basically dots + lines in a Lewis diagram))

Dilution

M₁V₁=M₂V₂

K_sp (solubility constant)

[A⁺][B^-] where AB dissolves into A⁺ and B^-. The exponents = coefficients in the balanced equation (just like K_c).

% ionization

[x]/[acid or base] * 100

Arrhenius equation

k = Ae^E_a/RT where A = frequency factor (not assessed). The core of this equation: decrease in E_a leads to an increase in K and increase in T leads to an increase in k.

Calculating ΔH°_rxn with bond energy

Σ(bond energy of reactants) - Σ(bond energy of products). Important note: when you calculate ΔH°_rxn with ΔH°_{f reactant} and ΔH°_{f product}, it’s the other way around: ΔH°_{f products} - ΔH°_{f reactants} (also in the formula sheet).

Strong acids

HCl, HBr, HI, HClO₄, HClO₃, H₂SO₄ (only the first proton), HNO₃

Strong bases

LiOH, NaOH, KOH, Ca(OH)₂, RbOH, Sr(OH)₂, CsOH, Ba(OH)₂. Important: Be(OH)₂ and Mg(OH)₂ are exceptions because they precipitate when they react with an acid.

Auto-ionization of water

Endothermic process in which H₂O ionizes to form 2 H⁺ and O^2-. Leads to smaller pK_w and thus smaller pH and pOH in higher temperature.

pH at equivalence for strong and weak acids

strong acid: pH=7 at equivalence

weak acid: pH>7 at equivalence (due to the strong conjugate base reacting with H+ ions in water)

Amp (unit)

coulomb/s

Nernst equation

E = E° - (RT/nF) * ln Q

E°_cell in electrolysis

E°_cathode - E°_anode