Understanding Acid-Base Chemistry Fundamentals.pdf

🧬 9/8/24, 6:28 PM 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...

🧬 9/8/24, 6:28 PM 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." Example: HCl dissolving in water HCl + H2O → Cl- + H3O+ 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 Example HCl Cl- H2O To draw the conjugate base of any acid, just remove one proton (an H) from the acid and decrease its charge by +1. To draw the conjugate acid of any base, just add one proton (an 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 K and pK Values pK: a measure of an acid's strength K: a measure of a base's strength pK Value Low (e.g. 2) High (e.g. 16) Sorting Acids and Bases by Strength Use the mnemonic CARDIO to remember the factors that influence acidity: C: Charge A: Atom R: Resonance https://www.turbolearn.ai/content/ec709e0a-1308-4604-b35e-374aba5f280c 1/5 9/8/24, 6:28 PM Understanding Acid-Base Chemistry Fundamentals D: Dipole Induction I: Orbital hybridization O: Other factors Charge 🔋 If all other factors are the same, a more positively-charged compound is more acidic. If all other factors are the same, a more negatively-charged compound is more basic. Compound Charge H2O Neutral H3O+ Positive OH- Negative 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 CH4 Carbon H2O Oxygen HF Fluorine Resonance 🔄 Resonance increases the stability of charges. A more stable conjugate base means a stronger acid. Compound Resonance Alcohol 1 No resonance Alcohol 2 Resonance Dipole Induction 💡 Withdrawing groups increase acidity. Donating groups decrease acidity. Group Electron-withdrawing (e.g. F, Cl) Electron-donating (e.g. H, C) Orbital Hybridization 🌀 https://www.turbolearn.ai/content/ec709e0a-1308-4604-b35e-374aba5f280c 2/5 9/8/24, 6:28 PM Understanding Acid-Base Chemistry Fundamentals The more s-character an atom has, the more electronegative it is. Acidity increases as the atom's electronegativity increases. Orbital Hybridization Electronegativity sp3 Low sp2 Medium sp High 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 sp3 25% sp2 33% sp 50% 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+). 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 mnemonic CARDIO, which stands for: Charge Atom Resonance Dipole Induction Orbital hybridization Charge ⚖️ If all other factors are the same, the more positively-charged the compound, the more acidic it is. The more negatively-charged the compound, the more basic it is. Compound Charge HO -1 H2O 0 H3O+ +1 Atom ⚗️ If all other factors are about the same, a hydrogen's acidity increases as the atom it's bonded to: https://www.turbolearn.ai/content/ec709e0a-1308-4604-b35e-374aba5f280c 3/5 9/8/24, 6:28 PM Understanding Acid-Base Chemistry Fundamentals goes left-to-right across a row on the periodic table goes down a column on the periodic table Compound Atom CH4 C NH3 N H2O O HF F Resonance 🔄 For all acids and bases, the more stable the conjugate base, the stronger the acid. Resonance increases a conjugate base's stability, making the acid it came from more acidic. Less stable conjugate base → less acidic More stable conjugate base → more acidic Dipole Induction 💡 Withdrawing groups increase acidity, while donating groups decrease acidity. Orbital Hybridization 🌀 If all other factors are about the same, 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 16 pK 10 pK 5 pK 2 Amino Acids and pK Values 🧬 Amino acids are simple molecules with both a carboxylic acid part and an amine part. pKa Values 📊 pKa values tell us how acidic something is. The lower the pKa, the more acidic the proton. pKa = acidity Amino Acids and pH 🌀 Amino acids can never exist as uncharged compounds because a carboxylic acid (pKa 2) is more acidic than an NH+ (pKa 9-10). Predicting an Amino Acid's Form 🔮 To predict an amino acid's form at a given pH, use the following rules: Every group whose pKa is below the pH will be deprotonated (O for oxygens, neutral N for nitrogens). Every group whose pKa is above the pH will be protonated (OH for oxygens, N+ for nitrogens). Example: Histidine https://www.turbolearn.ai/content/ec709e0a-1308-4604-b35e-374aba5f280c 4/5 9/8/24, 6:28 PM Understanding Acid-Base Chemistry Fundamentals pKa pH 0 pH 4 pH 8 2.0 protonated protonated deprotonated 6.0 protonated protonated protonated 9.0 protonated protonated protonated https://www.turbolearn.ai/content/ec709e0a-1308-4604-b35e-374aba5f280c 5/5