Chp. 2.2.pdf

🧬 9/9/24, 11:48 AM Understanding Acid-Base Chemistry Fundamentals Acid-Base Chemistry Brnsted Acids and Bases A Brnsted acid is a substance that donates H+ ions (protons). A Brnsted bas...

🧬 9/9/24, 11:48 AM Understanding Acid-Base Chemistry Fundamentals Acid-Base Chemistry Brnsted Acids and Bases A Brnsted acid is a substance that donates H+ ions (protons). A Brnsted base is a substance that accepts H+ ions. "A Brnsted acid is a proton donor, while a Brnsted base is a proton acceptor." For example, consider the reaction of HCl dissolving in water: HCl + H2O → Cl- + H3O+ HCl is the Brnsted acid (donates H+ ions) H2O is the Brnsted base (accepts H+ ions) Lewis Acids and Bases A Lewis acid is a substance that accepts electrons. A Lewis base is a substance that donates electrons. "A Lewis acid is an electron pair acceptor, while a Lewis base is an electron pair donor." Conjugate Acids and Bases In any acid-base reaction, the product that comes from the acid is called the conjugate base. The product that comes from the base is called the conjugate acid. Acid Conjugate Base Base Conjugate Acid Example HCl Cl- H2O H3O+ To draw the conjugate base of any acid, remove one proton (H) from the acid and decrease its charge by +1. To draw the conjugate acid of any base, add one proton (H) to the base and increase its charge by +1. The Conjugate Base-Acid Relationship The stronger the acid, the weaker its conjugate base. The stronger the base, the weaker its conjugate acid. "A strong acid has a weak conjugate base, while a strong base has a weak conjugate acid." pH Scale 📊 The pH scale is a numerical measure of how acidic or basic a solution is. The pH scale ranges from 0 to 14. pH 7.0: neutral solution pH < 7.0: acidic solution pH > 7.0: basic solution K and pK Values 📊 K: a measure of acid strength pK: a measure of base strength pK Value Acid Strength Low pK Strong acid High pK Weak acid https://www.turbolearn.ai/content/b153ca9b-2025-410b-b633-1cf33728b804 1/4 9/9/24, 11:48 AM Understanding Acid-Base Chemistry Fundamentals pK Value Base Strength Low pK Strong base High pK Weak base Sorting Acids and Bases by Strength 🔍 Use the mnemonic CARDIO to remember the factors that influence acidity: C: Charge A: Atom R: Resonance D: Dipole Induction I: Orbital Hybridization O: Other factors Charge ⚡️ More positively charged compounds are more acidic. More negatively charged compounds are more basic. Compound Charge pK HO- -1 15.7 H2O 0 7.0 H3O+ +1 -1.7 Atom ⚗️ Acidity increases as you go left-to-right across a row on the periodic table. Acidity increases as you go down a column on the periodic table. Compound Atom pK CH4 C 48 NH3 N 38 H2O O 15.7 HF F 3.2 Resonance 🔄 Resonance increases the stability of charges. More stable conjugate bases are weaker acids. https://www.turbolearn.ai/content/b153ca9b-2025-410b-b633-1cf33728b804 2/4 9/9/24, 11:48 AM Understanding Acid-Base Chemistry Fundamentals Compound Resonance pK CH3OH No resonance 16 CH3O- Resonance 10 Dipole Induction 💡 Withdrawing groups increase acidity. Donating groups decrease acidity. Compound Group pK CH3F Withdrawing 3.2 CH3CH3 Donating 48 Orbital Hybridization 🔩 More s-character in an atom increases its electronegativity. More electronegative atoms increase acidity. Atom s-Character pK sp3 25% 25 sp2 33% 44 sp 50% 48 Orbital hybridization affects the acidity of an atom. The more s-character an atom has, the more electronegative it is, and the more acidic Hs bonded to it will be. Hybridization % s-character pK sp3 25% 25 sp2 33% 16 sp 50% 48 Conjugate Acids and Bases 🔄 In any acid-base reaction, the product that comes from the acid is called the conjugate base, and the product that comes from the base is called the conjugate acid. "The conjugate base of an acid is the species formed when the acid donates a proton (H+), while the conjugate acid of a base is the species formed when the base accepts a proton." To draw the conjugate base of an acid, remove one proton (H) from the acid and decrease its charge by +1. To draw the conjugate acid of a base, add one proton (H) to the base and increase its charge by +1. Sorting Acids and Bases by Strength 🔍 To sort acids or bases by strength, use the CARDIO mnemonic: Charge: The more positively-charged the compound, the more acidic. Atom: The more electronegative the atom, the more acidic. https://www.turbolearn.ai/content/b153ca9b-2025-410b-b633-1cf33728b804 3/4 9/9/24, 11:48 AM Understanding Acid-Base Chemistry Fundamentals Resonance: The more stable the conjugate base, the stronger the acid. Dipole Induction: Withdrawing groups increase acidity, while donating groups decrease acidity. 📊 Orbital Hybridization: The more s-character an atom has, the more electronegative it is, and the more acidic Hs bonded to it will be. Important pK Values pK Value Description 16 pK of a typical sp3-hybridized acid 10 pK of a typical sp2-hybridized acid 5 pK of a typical sp-hybridized acid 2 pK of a typical carboxylic acid 20 pK of a typical amine Amino Acids and pK Values 🧬 Amino acids have both a carboxylic acid part and an amine part. The pK values of these groups determine the overall charge of the amino acid. Group pK Value Carboxylic acid 2 Amine 9-10 Amino Acids and pH 🌡️ Amino acids can never exist as uncharged compounds because the carboxylic acid group is more acidic than the amine group. At low pH, amino acids will exist in their protonated form. At high pH, amino acids will exist in their deprotonated form. Predicting an Amino Acid's Form 🔮 To predict the form an amino acid will take at a given pH, use the following rules: Every group whose pK is below the pH will be deprotonated (O for oxygens, neutral N for nitrogens). Every group whose pK is above the pH will be protonated (OH for oxygens, N+ for nitrogens). Example: Histidine pH pK Values Form 0 2.0, 6.0, 9.0 Protonated 4 2.0, 6.0, 9.0 Partially deprotonated 8 2.0, 6.0, 9.0 Deprotonated 12 2.0, 6.0, 9.0 Fully deprotonated https://www.turbolearn.ai/content/b153ca9b-2025-410b-b633-1cf33728b804 4/4