ACIDS AND BASES

EQ: What is an acid. What is a base EQ: What is an acid? What is a base? What happens when acids and bases react?

DEFINITIONS Basic: Acid = tastes sour, strong smell Base = tastes bitter, feels slippery/soapy (Both cause burns if concentrated)

DEFINITIONS Arrhenius: Brønsted-Lowry: Acid = produces H+ in solution Base = produces OH- in solution Brønsted-Lowry: Acid = proton donor Base = proton acceptor

NEUTRALIZATION REACTIONS HA + BOH ⟷ BA + HOH acid + base salt + water Example: Nitric acid is added to potassium hydroxide: HNO3 + KOH ⟷ KNO3 + H2O

Acid/Base Stoichiometry (similar to solution stoich.) A 10 mL sample of 1.5 M hydrochloric acid requires 20 mL of sodium hydroxide to completely neutralize. What molarity is the sodium hydroxide? “Neutralize” = react acid and base exactly so there is no excess. HCl + NaOH ⟷ NaCl + H2O 10 mL 20 mL 1.5 M ? M 0.01 𝐿 𝐻𝐶𝑙 𝑥 1.5 𝑚𝑜𝑙 𝐻𝐶𝑙 𝐿 𝐻𝐶𝑙 𝑥 1 𝑚𝑜𝑙 𝑁𝑎𝑂𝐻 1 𝑚𝑜𝑙 𝐻𝐶𝑙 =0.015 𝑚𝑜𝑙 𝑁𝑎𝑂𝐻 𝑀= 0.15 𝑚𝑜𝑙 𝑁𝑎𝑂𝐻 0.020 𝐿 =0.75 𝑀

EQ: What is a strong acid. How is [H+] and [OH-] calculated EQ: What is a strong acid? How is [H+] and [OH-] calculated? How is pH Calculated?

Strong Acids & Bases (Completely Dissociate/Ionize) HCl, HNO3, H2SO4, HClO4 HA ⟷ H+ + A- [HA] = [H+] BASES LiOH, NaOH, KOH, RbOH BOH ⟷ B+ + OH- [BOH] = [OH-]

Acid/Base Equilibrium Water autoionizes (it naturally exists both in its liquid form and its ion form H2O ⟷ H+ + OH- Equilibrium constant for Water (Kw); “Water Dissociation Constant” Kw = [H+][OH-] = 1 x 10-14 (experimentally determined, at 25˚C) Can use this equation to solve for [H+] or [OH-] when you know the other

pH pH = - log [H+] pH < 7 ➝ Acidic pH = 7 ➝ Neutral pOH = - log [OH-] [OH-] = 10-pOH pH + pOH = 14 pH < 7 ➝ Acidic pH = 7 ➝ Neutral (pure H2O) pH > 7 ➝ Basic

What if a reaction isn’t perfectly neutralized? 100 mL of 2.0 M sodium hydroxide is combined with 75 mL of 3.0 M hydrochloric acid. What is the limiting reagent, what is the excess reagent, and what is the pH of the resulting solution? NaOH + HCl ⟷ NaCl + H2O 0.100 𝐿 𝑁𝑎𝑂𝐻 𝑥 2.0 𝑚𝑜𝑙 𝑁𝑎𝑂𝐻 𝐿 =0.2 𝑚𝑜𝑙 𝑁𝑎𝑂𝐻 0.075 𝐿 𝐻𝐶𝑙 𝑥 3.0 𝑚𝑜𝑙 𝐻𝐶𝑙 𝐿 =0.225 𝑚𝑜𝑙 𝐻𝐶𝑙 Mole Ratio: 1 mol NaOH per 1 mole HCl NaOH is limiting, HCl is in excess 0.025 mol of HCl remains after the reaction 𝑀= 0.025 𝑚𝑜𝑙 𝐻 + 0.100 𝐿+0.075 𝐿 =0.143 𝑀 pH = - log (0.143M) = 0.845

EQ: What is a titration? How is the equivalence point of a titration determined?

Titrations Method used to determine the unknown concentration of an acid or base The systematic addition of a base to an acid (or visa versa) The concentration of the titrant used must be known The volume of titrant required to reach equivalence point is used to determine the unknown concentration of acid or base.

Titrations Equivalence Point: Indicators: The point at which all of the acid present has reacted exactly with all of the base (aka “perfectly neutralized”) Indicators: A chemical added to a titration that will change the color of the solution at the equivalence point. Common Indicator = Phenolphthalein (PHTH) Colorless in acid, Pink in base