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Acids and Bases

Acids and Bases

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Acids and Bases

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  1. Acids and Bases Chemistry

  2. Taste sour pH less than 7 Turns blue litmus paper to red (BRA) Form H+ ions (Hydrogen) in solution Corrosive React with most metals to form Hydrogen gas * Good conductors of electricity React with bases What are the properties of acids?

  3. What are the properties of bases or alkaline? • Taste bitter • pH greater than 7 • Turns red litmus paper to blue (RBB) • Form OH- (hydroxide ions) in a solution • Feels soapy or slippery • React with fats to make soap • Dissolves fats and oils • Reacts with acids and neutralizes it

  4. What is a pH? • pH measures how acidic or basic is the substance

  5. pH scale pH 1-6 – ACID pH 1 – strong acid pH 6 – weak acid pH 7 – neutral pH 8-14 – weak base pH 8 – strong base

  6. What is a salt • A salt is a neutral substance produced from reaction of an acid and a base

  7. Concept map

  8. 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

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

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

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

  12. 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

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

  14. 100% dissociation of HA HA H+ Strong Acid A- Would the solution be conductive?

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

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

  17. 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

  18. 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

  19. 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

  20. 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

  21. 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

  22. - 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+

  23. 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)

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

  25. 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

  26. 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

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

  28. 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

  29. 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