Transcript A_B2
Acids and Bases General Properties ACIDS Taste sour Turn litmus React with active metals – Fe, Zn to form Hydrogen gas BASES Taste bitter Turn litmus Feel soapy or slippery (react with fats to make soap) React with acids React with bases blue to red red to blue Definitions Arrehenius only in water Bronsted-Lowry any solvent Lewis used in organic chemistry, wider range of substances Acids – produce H+ Bases - produce OHAcids – donate H+ Bases – accept H+ Acids – accept e- pair Bases – donate e- pair Examples Arrhenius NaOH HCl Bronsted-Lowry HCl Lewis BF3 HCN :NH3 NH3 Let’s examine the behavior of an acid, HA, in aqueous solution. HA What happens to the HA molecules in solution? 100% dissociation of HA HA H+ Strong Acid AWould the solution be conductive? Partial dissociation of HA HA H+ Weak Acid AWould the solution be conductive? HA H+ + A- HA H+ A- Weak Acid At any one time, only a fraction of the molecules are dissociated. acid rain (NOx, SOx) pH of 4.2 - 4.4 in Washington DC area pH 0-14 scale for the chemists 2 3 4 5 acidic (H+) > (OH-) normal rain (CO2) pH = 5.3 – 5.7 6 7 8 neutral @ 25oC (H+) = (OH-) distilled water fish populations drop off pH < 6 and to zero pH < 5 9 10 11 basic or alkaline (H+) < (OH-) natural waters pH = 6.5 - 8.5 12 pH of Rainwater across United States in 2001 You are here! Why is the eastern US more acidic? http://nadp.sws.uiuc.edu/isopleths What is acid rain? Dissolved carbon dioxide lowers the pH CO2 (g) + H2O H2CO3 H+ + HCO3- Atmospheric pollutants from combustion NO, NO2 + H2O … HNO3 SO2, SO3 + H2O … H2SO4 pH < 5.3 both strong acids pH The biological view in the human body acidic 1 2 3 4 5 6 basic/alkaline 7 8 9 10 Tortora & Grabowski, Prin. of Anatomy & Physiology, 10th ed., Wiley (2003) 11 Does the pH influence the activity of an enzyme? Trypsin is a digestive enzyme. Where? Intestinal pH range 7.0-8.5 The amino acid glycine - amphoteric It’s an acid and a base! Gain of H+ Loss of H+ H3N+-CH2-COOH H2N-CH2-COOH H2N-CH2-COOChime structure The amino acid glycine - Zwitterion formation Transfer of H+ from carboxylic acid group to amine group. + A dipolar ion forms. H2N-CH2-COOH Chime structure H3N+-CH2-COOintramolecular acid-base reaction When life goes either way amphoteric (amphiprotic) substances Acting like a base + H+ H2CO3 accepts H+ HCO3- Acting like an acid - H+ CO3-2 donates H+ Show how water can be amphoteric. H2O + H+ - H+ Strong and Weak Acids/Bases Strong acids/bases – 100% dissociation into ions HCl HNO3 H2SO4 NaOH KOH Weak acids/bases – partial dissociation, both ions and molecules CH3COOH NH3 The Bronsted-Lowry Concept Conjugate pairs HCl Cl- NH4+ NH3 CH3COOH CH3COO- HNO3 NO3- How does a conjugate pair differ? H+ transfer Neutralization In general: Acid + Base Salt + Water All neutralization reactions are double displacement reactions. HCl + NaOH NaCl + HOH HCl + Mg(OH)2 H2SO4 + NaHCO3 Does pure water conduct electrical current? Water is a very, very, very weak electrolyte. H2O H+ + OH- How are (H+) and (OH-) related? (H+)(OH-) = 10-14 For pure water: (H+) = (OH-) = 10-7M This is neutrality and at 25oC is a pH = 7. water Behavior of oxides in water– Group A basic 1A amphoteric acidic 3A 4A 5A 6A 7A 2A Group B 105 Db 107 Bh basic: Na2O + H2O 2NaOH (O-2 + H2O 2OH-) acidic: CO2 + H2O H2CO3 8A Dilution water (solvent) solute moles of solute remain constant Vfinal diluted, Mfinal molesinitial = molesfinal Vinitial concentrated, Minitial adding water lowers the solute concentration Mfinal x Vfinal = Minitial x Vinitial Titration Calculation HCl + NaOH indicator NaCl + HOH A way to analyze solutions! at equivalence point: moleHCl = moleNaOH moles = M x VL Macid x Vinitial acid = Mbase x Vburet