Acids/Bases

Properties of Acids pp 186

Properties of Bases pp 186

Arrhenius Model of Acid/Base Acid Produces H + /H 3 O + (hydronium) when in solution HA + H 2 O  H 3 O + + A - HCl + H 2 O  H 3 O + + Cl - Base Produces OH - when in solution BOH  B + + OH - NaOH  Na + + OH -

Strong vs. Weak Strong Acid/Base dissociates 100% HA + H 2 O  H 3 O + + A - No HA or BOH left over in solution Weak acid or base only has less than 5% dissociation. Large amounts of HA or BOH left in solution – will establish equilibrium Strong Acids: HCl, HBr, HI, HNO 3, H 2 SO 4, HClO 4 Strong Bases: Group I metal hydroxides Anything else is considered weak. Strength has no indication on power of the acid/base…only describes its behavior in water

Brønsted-Lowery Model an acid is a H + donor HA + H 2 O  H 3 O + + A - HNO 3 + H 2 O  H 3 O + + NO 3 - When an acid donates a H +, a conjugate base is formed A - (is capable of accepting a H + ). a base is a H + acceptor B + H 2 O  BH + + OH - NH 3 + H 2 O  NH OH - Notice OH - is still produced but it is coming from the water When a base accepts a hydrogen ion, a conjugate acid is formed BH + (is capable of donating a H + ).

Identify Conjugate Acid Base Pairs HClO 2 (aq) + H 2 O (l) H 3 O + (aq) + ClO 2 - (aq) AcidBase CA CB pp

Lewis Model Acid Accepts a lone pair of electrons from base Base Donates a lone pair of electrons to the acid

Auto Ionization of Water Water is an amphoteric substance, can act as both an acid and a base H 2 O + H 2 O H 3 O + + OH - At 25°C [H 3 O + ] = [OH - ] = 1.0 x M Ion product constant for water Kw = 1.0 x Kw = [H3O+] [OH-] pp 224

pH pH – the power of hydrogen pH scale 0-14 – Value can be greater than 14 or less than 0 pH = -log[H + ] If the [H + ] > 1.0 x (pH <7) acidic If the [H + ] 7) basic If the [H + ] = 1.0 x (pH =7) neutral [H+] = 10 -pH

pOH pOH – the power of hydroxide pOH scale 0-14 Value can be greater than 14 or less than 0 pH = -log[OH - ] If the [OH-] > 1.0 x 10-7 (pH <7) basic If the [OH-] 7) acidic If the [OH-] = 1.0 x 10-7 (pH =7) neutral [OH-] = 10 -pOH pH + pOH =14

Calculating the pH of weak Acid/Base Weak Acid does not have complete dissociation therefore need to calculate the concentration of H + in solution at equilibrium Ka = Kb = Kw = Ka x Kb

Calculate the pH of 3.00 M acetic acid at 25°C with a Ka = 1.8 x 10 -5

Calculate the pH of 3.00 M NH 3 at 25°C with a Kb = 1.8 x 10 -5

Acid/Base Neutralization

Acid/Base Titration The general process of determining the molarity of an acid or a base through the use of an acid-base reaction is called an acid-base titration. The known reactant molarity is used to find the unknown molarity of the other solution. MVn =MVn

Tritration Curves Equivalence point mol H + = mol OH - (inflection point on curve) End point when the indicator changes color – Indicator is a substance that is pH sensitive Want the equivalence point and end point to be the same Choose an indicator based on equivalence point

Strong Acid/Strong Base Equivalence pt occurs at about pH of 7.0

Weak Acid/Strong Base Equivalence pt >7 usually around 9

Strong Acid/Weak Base At equivalence pt pH<7 usually around 5

Common Indicators