Acid/Base Reactions

Brønsted-Lowry – proton donor Arrhenius – acids produce H+ ions in water HCl H+ + Cl-

HCl, HBr, HI, H2SO4, HC2H3O2

Acids

Brønsted-Lowry – proton acceptor Arrhenius – bases produce OH- ions in water NaOH Na+ + OH-

NaOH, KOH, LiOH, Ba(OH)2, Ca(OH)2

Bases

Net ionic equation for acid-base reactions H+ + OH- H2O Acid + base H2O + salt

Acid-Base Reactions

Procedure for determining the concentration of an unknown acid (or base) solution using a known concentration of a base (or acid)

Titrant – solution of known concentration Analyte – solution of unknown concentration

◦ Known volume Indicator – substance added at the

beginning of the titration that changes color at the equivalence point

Titrations

Equivalence Point - Point at which exactly enough base solution has been added to the acid until the acid is neutralized

Concentration (M) and volume (V) of base are known, number of moles of acid can be calculated

moles of acid neutralized

Acid concentration = liters of acid solution

Titrations

What volume of 0.900 M HCl is required to completely neutralize 25.0 g of Ca(OH)2?

1. Write and balance the equation 2. Determine number of moles of Ca(OH)2

3. Determine the number of moles of HCl required to neutralize

4. Determine the volume of acid that contains the required amount of moles of HCl

Example

More on Acids & Bases

Acids - Donate H+ into solution◦ Acidic solutions have lots of H+ ions◦ Proton donors

Bases – Donate OH- into solutions◦ Basic solutions have lots of OH- ions◦ Proton acceptors

Water is a nonelectrolyte◦ Doesn’t exist as ions in solution◦ H+ + OH- H2O

Acids/Bases

Strong acids and bases completely dissociate into ions◦ Acids produce H+ (or H3O+)◦ Bases produce OH-

Weak acids/bases cannot dissociate as easily◦ Weak acids only partially dissociates in water to

give H+ and an anion HF H+ + F-

◦ Weak bases – most are anions of weak acids Don’t give OH-, react with water to form OH-

C2H3O2- (weak base) from HC2H3O2 (weak acids)

Strength

Conjugate pairs – acid and base pair◦ One can accept a proton and the other can

donate NH3 + H2O NH4

+ +OH-

NH3 (base) NH4+ (conjugate acid)

H2O (acid) OH- (conjugate base)

Stronger acid/base, weaker the conjugate

Conjugates

A student carries out an experiment to standardize (determine the concentration of) a NaOH solution. The student weighs out 1.3009 g of potassium hydrogen phthalate (KHP – KHC8H4O4). KHP has one acidic hydrogen. The student dissolves the KHP in distilled water, adds phenolphthalein, and titrates the resulting solution with the NaOH solution to the endpoint. The difference between the final and initial burette readings is 41.20 mL. Calculate the concentration of NaOH solution.

Warm-Up