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  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.

Types AcidsBases Arrhenius produce H + in aqueous solution produce OH - in aqueous solution Lewis electron acceptors in solution electron donors in solution Bronsted-Lowry proton donorsproton acceptors

Weak Acids and Bases Weak Acids and Bases dissociate 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 - NH 3 + H 2 O  NH OH - - HSO H 2 O  SO H 3 O +

Strong Acids and Bases Strong Acids and Bases dissociate completely and are irreversible. Large K a and K b. Ionize completely in water. Reactions between strong acids and strong bases are called neutralizing reactions. Example - H 2 SO 4 molecules do not exist in water; rather, only H 3 O + and HSO 4 - are present. - HBr + KOH  K + + Br - + H 2 0 Strong Acids: HCl, HBr, HI, HNO 3, H 2 SO 4, HClO 4. Strong Bases: LiOH, NaOH, KOH, Group 1 hydroxides.

The Generic Equations Generic Acid Equation: HX (aq) + H 2 O (l)  H 3 O + (aq) + X - (aq) Ka = [H 3 O + ][X - ] [HX] Generic Base Equation: X - + H 2 O (l)  HX + OH - Kb = [HX][OH - ] [X - ]

The pH Scale K w = 1 x = [H + ][OH - ] = K a x K b 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 K a = 4.6 x find K b and pH.

Polyprotic Acids Acids that contain more than 1 dissociable H +. Example H 2 SO 4 is only strong for the 1 st H + ion that dissociates completely; the 2 nd is a weak acid. H 2 SO 4 + H 2 O  HSO H 3 O + HSO H 2 O  SO H 3 O +

Conjucate Acid-Base Pairs Acid  Conjugate Base + H + Example HCO H 2 0  H CO32- Acid Base Conj. Conj. Acid Base  Stronger Acids form Weaker Conjugate Bases.  Stronger Bases form Weaker Conjugate Acids. Equilibrium shifts toward the side of the reaction having the weaker acid and base. DID YOU KNOW?

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: HNO 3 and Phosphoric Acid: H 3 PO 4 HNO 3 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.

Titrations Let’s work one on the board shall we? KEEP IN MIND - pH before adding base = pK a1 - At mid-point: pH = pK a - Always check whether the solution is acting as an acid or a base at the equivilence point. - N A C A V A = N B C B V B

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 = pK a + log([A - ]/[HA])

The End mmmmmm…..no more acids.