Acids and Bases - Prince George's Community College：酸和碱-乔治王子社区学院

1、Acids and Bases,PGCC CHM 101 Sinex,General properties,ACIDS Taste sour Turn litmus React with active metals Fe, Zn React with bases,BASES Taste bitter Turn litmus Feel soapy or slippery (react with fats to make soap) React with acids,blue to red,red to blue,Definitions,Acids produce H+ Bases - produ

2、ce OH- Acids donate H+ Bases accept H+ Acids accept e- pair Bases donate e- pair,Arrehenius,Bronsted-Lowry,Lewis,only in water,any solvent,used in organic chemistry, wider range of substances,Examples,Arrhenius,Bronsted-Lowry,Lewis,HCl,NaOH,HCl,NH3,:NH3,BF3,HCN,The hydrogen ion in aqueous solution,H

3、+ + H2O H3O+ (hydronium ion),The Bronsted-Lowry Concept,Conjugate pairs,HCl Cl-,CH3COOH CH3COO-,NH4+ NH3,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,H

4、Cl + Mg(OH)2 ,H2SO4 + NaHCO3 ,H2O H+ + OH-,Does pure water conduct electrical current?,(H+)(OH-) = 10-14,For pure water: (H+) = (OH-) = 10-7M,This is neutrality and at 25oC is a pH = 7.,Water is a very, very, very weak electrolyte.,How are (H+) and (OH-) related?,water,HA,Lets examine the behavior o

5、f an acid, HA, in aqueous solution.,What happens to the HA molecules in solution?,HA,H+,A-,Strong Acid,100% dissociation of HA,Would the solution be conductive?,HA,H+,A-,Weak Acid,Partial dissociation of HA,Would the solution be conductive?,HA,H+,A-,Weak Acid,HA H+ + A-,At any one time, only a fract

6、ion of the molecules are dissociated.,Strong and Weak Acids/Bases,Strong acids/bases 100% dissociation into ions HClNaOH HNO3KOH H2SO4,Weak acids/bases partial dissociation, both ions and molecules CH3COOHNH3,pH,2,3,4,5,6,7,8,9,10,11,12,neutral 25oC (H+) = (OH-) distilled water,acidic (H+) (OH-),bas

7、ic or alkaline (H+) (OH-),natural waters pH = 6.5 - 8.5,normal rain (CO2) pH = 5.3 5.7,acid rain (NOx, SOx) pH of 4.2 - 4.4 in Washington DC area,0-14 scale for the chemists,fish populations drop off pH 6 and to zero pH 5,You are here!,/isopleths,pH of Rainwater across United

8、States in 2001,Why is the eastern US more acidic?,air masses,What is acid rain?,CO2 (g) + H2O H2CO3 H+ + HCO3-,Dissolved carbon dioxide lowers the pH,Atmospheric pollutants from combustion,NO, NO2 + H2O HNO3,SO2, SO3 + H2O H2SO4,both strong acids,pH 5.3,Behavior of oxides in water Group A,basic,amph

9、oteric,acidic,3A 4A 5A 6A 7A,1A,2A,8A,Group B,basic: Na2O + H2O 2NaOH (O-2 + H2O 2OH-),acidic: CO2 + H2O H2CO3,When life goes either way amphoteric (amphiprotic) substances,HCO3-,H2CO3,CO3-2,Acting like a base,Acting like an acid,accepts H+,donates H+,pH,1,2,3,4,5,6,8,9,10,11,The biological view in

10、the human body,gastric juice,vaginal fluid,urine,saliva,cerebrospinal fluid,blood,pancreatic juice,bile,acidic,basic/alkaline,7,Tortora & Grabowski, Prin. of Anatomy & Physiology, 10th ed., Wiley (2003),Does the pH influence the activity of an enzyme?,Trypsin is a digestive enzyme. Where?,Intestinal

11、 pH range 7.0-8.5,The amino acid glycine - amphoteric Its an acid and a base!,Loss of H+,Gain of H+,H2N-CH2-COOH,H3N+-CH2-COOH,H2N-CH2-COO-,Chime structure,The amino acid glycine - Zwitterion formation,Transfer of H+ from carboxylic acid group to amine group.,H2N-CH2-COOH,H3N+-CH2-COO-,+,-,A dipolar

12、 ion forms.,intramolecular acid-base reaction,Chime structure,Show how water can be amphoteric.,H2O,Dilution,water (solvent),solute,concentrated, Minitial,diluted, Mfinal,adding water lowers the solute concentration,moles of solute remain constant,Vinitial,Vfinal,molesinitial = molesfinal,Mfinal x Vfinal = Minitia