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Acids and Bases

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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

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  1. Acids and Bases PGCC CHM 101 Sinex

  2. 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

  3. 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

  4. Examples The hydrogen ion in aqueous solution H+ + H2O  H3O+ (hydronium ion) Arrhenius HCl NaOH Bronsted-Lowry HCl HCN NH3 :NH3 Lewis BF3

  5. The Bronsted-Lowry Concept Conjugate pairs CH3COOHCH3COO- HCl Cl- NH4+NH3 HNO3NO3- How does a conjugate pair differ? H+transfer

  6. Neutralization In general: Acid + Base  Salt + Water All neutralization reactions are double displacement reactions. HCl + NaOH  NaCl + HOH HCl + Mg(OH)2 H2SO4 + NaHCO3

  7. 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

  8. Let’s examine the behavior of an acid, HA, in aqueous solution. HA What happens to the HA molecules in solution?

  9. 100% dissociation of HA HA H+ Strong Acid A- Would the solution be conductive?

  10. Partial dissociation of HA HA H+ Weak Acid A- Would the solution be conductive?

  11. HA  H+ + A- HA H+ Weak Acid A- At any one time, only a fraction of the molecules are dissociated.

  12. 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

  13. 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

  14. 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

  15. What is acid rain? Dissolved carbon dioxide lowers the pH CO2 (g) + H2O  H2CO3H+ + HCO3- Atmospheric pollutants from combustion NO, NO2 + H2O …  HNO3 both strong acids SO2, SO3 + H2O …  H2SO4 pH < 5.3

  16. 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

  17. - 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+

  18. 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)

  19. Does the pH influence the activity of an enzyme? Trypsin is a digestive enzyme. Where? Intestinal pH range 7.0-8.5

  20. 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

  21. 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

  22. - H+ + H+ Show how water can be amphoteric. H2O

  23. 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

  24. 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

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