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Acids and Bases

Acids and Bases. Max Bormes, Brittany Howse, Joe Stein, Kathy Adamczyk. Terminology. Acid : Any substance that when dissolved in pure water, increases the concentration of H + in the water. [0, 7) on the pH scale. Turns litmus paper red . Turns clear in phenolphthalein. Terminology.

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Acids and Bases

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  1. Acids and Bases Max Bormes, Brittany Howse, Joe Stein, Kathy Adamczyk

  2. Terminology • Acid: Any substance that when dissolved in pure water, increases the concentration of H+in the water. • [0, 7) on the pH scale. • Turns litmus paper red. • Turns clear in phenolphthalein.

  3. Terminology • Base: Any substance that when dissolved in pure water, increases the concentration of OH- in the water. • (7, 14] on the pH scale. • Turns litmus paper blue. • Turns pink in phenolphthalein.

  4. Types

  5. Weak Acids and Bases • Weak Acids and Basesdissociate partially in water. • The vast majority of acids and bases are weak. • The relative strength of an acid or base can be expressed quantitatively with an equilibrium constant. Example - NH3 + H2O  NH4+ + OH- - HSO4- + H2O  SO42- + H3O+

  6. Strong Acids and Bases • Strong Acids and Basesdissociate completely and are irreversible. • Large Ka and Kb. • Ionize completely in water. • Reactions between strong acids and strong bases are called neutralizing reactions. Strong Acids: HCl, HBr, HI, HNO3, H2SO4, HClO4. Strong Bases: LiOH, NaOH, KOH, Group 1 hydroxides. Example - H2SO4 molecules do not exist in water; rather, only H3O+ and HSO4- are present. - HBr + KOH  K+ + Br- + H20

  7. The Generic Equations • Generic Acid Equation: • HX(aq) + H2O(l) H3O+(aq) + X-(aq) • Ka = [H3O+][X-] [HX] • Generic Base Equation: • X- + H2O(l) HX + OH- • Kb = [HX][OH-] [X-]

  8. The pH Scale • Kw = 1 x 10-14 = [H+][OH-] = Ka x Kb • pH = -log [H+] • pOH = -log [OH-] = 14 – pH FUN FACT! You can find pH without a calculator!!!...sorta If [H+] = 10-x, pH = x. Ex) for 10-8, pH = 8. On the board: if Ka = 4.6 x 10-5 find Kb and pH.

  9. Polyprotic Acids • Acids that contain more than 1 dissociable H+. Example H2SO4 is only strong for the 1st H+ ion that dissociates completely; the 2nd is a weak acid. H2SO4 + H2O  HSO4- + H3O+ HSO4- + H2O  SO42- + H3O+

  10. Conjucate Acid-Base Pairs • Acid  Conjugate Base + H+ Example HCO3- + H20H30+ + CO32- Acid BaseConj.Conj. AcidBase • Stronger Acids form Weaker Conjugate Bases. • Stronger Bases form Weaker Conjugate Acids. DID YOU KNOW? Equilibrium shifts toward the side of the reaction having the weaker acid and base.

  11. Inductive Effect • The inductive effect explains how acidity is increased by the stronger attraction of electrons from adjacent bonds by a more electronegative atom. Example Nitric Acid: HNO3 and Phosphoric Acid: H3PO4 HNO3 has 2 additional oxygen atoms connected to the central atoms that increase the polarization of the molecule (Oxygen is very electronegative) and thus weakens the H-O bond. The Phosphoric Acid only has 1 Oxygen, so the H-O bond is stronger than the H-O bond in Nitric Acid, so it is less likely to dissociate completely. The more polar molecule makes it easier to dissolve in water since likes dissolve likes.

  12. Titrations Let’s work one on the board shall we? KEEP IN MIND - pH before adding base = pKa1 - At mid-point: pH = pKa - Always check whether the solution is acting as an acid or a base at the equivilence point. - NACAVA = NBCBVB

  13. Buffers –almost done • A solution that resists a change in pH when H+ or OH- ions are added. • A buffer is created by adding an excess of a weak acid and a conjugate base or a weak base and its conjugate acid. • pH = pKa + log([A-]/[HA])

  14. The End mmmmmm…..no more acids.

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