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Acids and Bases

Acids and Bases. 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. Definitions. Acids – produce H + Bases - produce OH -

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Acids and Bases

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  1. Acids and Bases

  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

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

  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 double displacement reactions. HCl + NaOH  NaCl + HO H HCl + Mg(OH)2 H2SO4 + NaHCO3

  7. Concentration and Strength • Concentration: • Molarity (M) • Moles of solute per liter of solution • Strength • Degree of dissociation • How much the ions split when it dissolves

  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. pH • Measures H+ concentration pH of 1 = 1 x 10-1 M H+ pH of 7 = 1 x 10-7 M H+ pH of 14 = 1 x 10-14 M H+

  15. pH indicators • Change color based on pH of the solution • Litmus Paper • Phenolphthalein • pH range 1-8.2 = colorless • pH range 8.3-10 = pink color

  16. - 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+

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

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