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Acids and Bases. PGCC CHM 101 Sinex. 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. General properties. blue to red. red to blue. Definitions.
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Acids and Bases PGCC CHM 101 Sinex
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 General properties blue to red red to blue
Definitions • Acids – produce H+ • Bases - produce OH- • Acids – donate H+ • Bases – accept H+ • Acids – accept e- pair • Bases – donate e- pair Arrehenius only in water Bronsted-Lowry any solvent Lewis used in organic chemistry, wider range of substances
Examples The hydrogen ion in aqueous solution H+ + H2O H3O+ (hydronium ion) Arrhenius HCl NaOH Bronsted-Lowry HCl HCN NH3 :NH3 Lewis BF3
The Bronsted-Lowry Concept Conjugate pairs CH3COOHCH3COO- HCl Cl- NH4+NH3 HNO3NO3- 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
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 A- Would the solution be conductive?
Partial dissociation of HA HA H+ Weak Acid A- Would the solution be conductive?
HA H+ + A- HA H+ Weak Acid A- At any one time, only a fraction 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
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 6 7 8 9 10 11 12 acidic (H+) > (OH-) neutral @ 25oC (H+) = (OH-) distilled water basic or alkaline (H+) < (OH-) normal rain (CO2) pH = 5.3 – 5.7 fish populations drop off pH < 6 and to zero pH < 5 natural waters pH = 6.5 - 8.5
Increasing acidity pH of Rainwater across United States in 2001 You are here! air masses 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 H2CO3H+ + HCO3- Atmospheric pollutants from combustion NO, NO2 + H2O … HNO3 both strong acids SO2, SO3 + H2O … H2SO4 pH < 5.3
105 Db 107 Bh Behavior of oxides in water– Group A basic amphoteric acidic 8A 1A 3A 4A 5A 6A 7A 2A Group B basic: Na2O + H2O 2NaOH (O-2 + H2O 2OH-) acidic: CO2 + H2O H2CO3
- H+ + H+ When life goes either way amphoteric (amphiprotic) substances Acting like a base Acting like an acid HCO3- H2CO3 CO3-2 accepts H+ donates H+
pH The biological view in the human body acidic basic/alkaline 1 2 3 4 5 6 7 8 9 10 11 blood saliva urine gastric juice pancreatic juice vaginal fluid bile cerebrospinal fluid 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 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-COO- H2N-CH2-COOH Chime 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-COO- intramolecular acid-base reaction
- H+ + H+ Show how water can be amphoteric. H2O
Dilution water (solvent) solute moles of solute remain constant diluted, Mfinal Vfinal molesinitial = molesfinal Vinitial concentrated, Minitial adding water lowers the solute concentration Mfinal x Vfinal = Minitial x Vinitial
Titration Calculation indicator HCl + NaOH NaCl + HOH A way to analyze solutions! at equivalence point: moleHCl = moleNaOH moles = M x VL Macid x Vinitial acid = Mbase x Vburet