University:
York University
Course:
CHEM 1001 | Chemical Dynamics
Academic year:

2022
Views:

361

Pages:

3
Author:

Niklas

Chapter 7 pH calculations pH = -log[H+] pOH = -log[OH-] pH = 14 - pOH Acids Sour taste Dissolve active metals, usually liberating H₂ Corrosive: Dissolve compounds that are otherwise hard to dissolve Turn litmus paper red Bases Slippery and bitter Dissolve oil and grease React with many metal ions to form precipitates Turn litmus paper blue Three Theories of Acid-Base Chemistry Arrhenius: Acids release H+ ions, bases release OH- ions in water. Brønsted-Lowry: Acids lose protons, bases gain protons. Upon proton transfer, HX becomes "deprotonated" to form X-, and H₂O becomes "protonated" to form H₃O+. Lewis: Bases donate electron pairs, acids accept electron pairs. Chapter 7 Conjugate Acids and Bases When an acid donates its proton to a base, the resulting species is the conjugate base. When a base accepts a proton from an acid, the resulting species is the conjugate acid. Acid Dissociation Constant (Ka) Ka = [H₃O+][A-] / [HA] Strong acids have Ka >> 1. Weak acids have Ka << 1. Base Dissociation Constant (Kb) Kb = [OH-][HA] / [A-] Strong bases have Kb >> 1. Weak bases have Kb << 1. Conjugate Pairs A table lists various acids and their corresponding conjugate bases, along with their strength (strong, weak, or spectator ion). Chapter 7 H+ and OH- are present at 10^-7 M from autodissociation of H₂O at room temperature. Conjugate Acids of Bases Acid dissociation of HF: HF → H+ + F- Ka = [H+][F-] / [HF] Base dissociation of F-: F- + H₂O → OH- + HF Kb = [OH-][HF] / [F-] Combined: Ka * Kb = [H+][F-] / [HF] * [OH-][HF] / [F-] = Kw For any conjugate pair, larger Ka means smaller Kb and vice versa. Acid & Base Strength Acid Strength: Strong acids (HCl, HNO₃, H₂SO₄) have Ka >> 1. Weak acids (H₃O+, H₂SO₃, H₂CO₃) have Ka << 1. Negligible acids (H₂O, CH₄) have Ka ≈ 0. Base Strength: Strong bases (OH-) have Kb >> 1. Weak bases (CH₃COO-, NH₃, CO₃²-) have Kb << 1. Negligible bases (H₂O, F-) have Kb ≈ 0. Oxyacids Oxyacids are central atoms with several attached oxygen atoms. Acid strength increases with increasing oxidation number of the central atom. General rule for uncharged oxyacids MxEOy: If y - x ≥ 2, then it is strong. If y - x ≤ 1, then it is weak. Increasing electronegativity of the central atom increases acid strength. The opposite is true for bases.