#Acids and Bases: Your Ultimate AP Chem Review 🧪

Hey, future AP Chem superstar! Let's break down acids and bases, making sure you're totally prepped for anything the exam throws your way. We'll go from the basics to the trickiest parts, and I'll throw in some memory aids and exam tips to make sure you're feeling confident.

#Acid-Base Definitions: Arrhenius vs. Brønsted-Lowry

#Arrhenius Definition

Arrhenius Acid: Increases the concentration of H+ ions in solution. Think of it as anything that spits out H+ in water.
Arrhenius Base: Increases the concentration of OH- ions in solution. It's all about releasing OH- into the water.

Example: HCl (hydrochloric acid) in water:

$HCl \rightarrow H^+ + Cl^-$
- HCl is an Arrhenius acid because it releases H+ ions.

Key Concept

Remember: Arrhenius is all about what happens in water – H+ or OH- release.

#pH and pOH

pH = −log[H3O+]
pOH = −log[OH−]
- These equations help us quantify the acidity or basicity of a solution.

#pH of Water

Water autoionizes:

$2H_2O \rightleftharpoons H_3O^+ + OH^-$
- Kw = [H3O+][OH−] = 1.0 × 10−14 at 25°C
- In pure water at 25°C, pH = pOH = 7.0 (neutral).
- 💡 Important: Kw is temperature-dependent, so neutral pH isn't always 7.0!

#Brønsted-Lowry Definition

Brønsted-Lowry Acid: A proton (H+) donor.
Brønsted-Lowry Base: A proton (H+) acceptor.

Think of it as a transfer reaction, where the acid gives away an H+ and the base takes it.

General Reaction:

$HA + B^- \rightleftharpoons HB + A^-$
- HA (acid) donates H+ to B- (base) forming HB and A-.

Exam Tip

Brønsted-Lowry is more versatile than Arrhenius because it doesn't require water as a solvent.

#The Hydronium Ion (H3O+)

When an acid dissolves in water, it donates its H+ to water, forming H3O+.
- Arrhenius view: HA ⇌ H+ + A-
- Brønsted view: HA + H2O ⇌ H3O+ + A-
- Both views are essentially the same, since [H+] = [H3O+], but the Brønsted view shows the H+ transfer.

#Conjugate Acids and Bases

In the reaction HA + B- ⇌ HB + A-:
- HB is the conjugate acid of B- (it's what B- becomes after gaining a proton).
- A- is the conjugate base of HA (it's what HA becomes after losing a proton).
- Think of conjugate pairs as partners in the acid-base dance.
- Caption: Conjugate acid-base pairs differ by only one proton (H+).
Strength Relationship:
- The weaker an acid/base, the stronger its conjugate base/acid.
- The conjugate of a strong acid/base has negligible acidity/basicity.

Memory Aid

Think of it like a seesaw: If the acid is strong, its conjugate base is weak, and vice versa.

#Final Exam Focus 🎯

High-Priority Topics:
- Acid-base definitions (Arrhenius, Brønsted-Lowry)
- pH and pOH calculations
- Identifying conjugate acid-base pairs
- Understanding the relationship between acid/base strength and conjugate strength
Common Question Types:
- Multiple-choice questions testing definitions and calculations
- Free-response questions involving acid-base reactions and titrations
Last-Minute Tips:
- Time Management: Don't get bogged down on one question. Move on and come back if needed.
- Common Pitfalls: Watch out for tricky wording and make sure to use correct units. Double-check your calculations!
- Strategies: Read questions carefully, underline key words, and show all your work for partial credit.

#Practice Questions

Practice Question

#Multiple Choice Questions

Which of the following is the conjugate base of H2PO4-? (A) H3PO4 (B) HPO42- (C) PO43- (D) H2PO4+
A solution has a pH of 3. What is the concentration of hydroxide ions, [OH-]? (A) 1 x 10-3 M (B) 1 x 10-11 M (C) 1 x 10-7 M (D) 1 x 10-14 M

#Free Response Question

A 25.0 mL sample of a 0.100 M solution of a weak monoprotic acid, HA, is titrated with a 0.100 M NaOH solution. The pH at the half-equivalence point is 4.80. (a) Write the balanced net ionic equation for the reaction between HA and NaOH. (b) Calculate the Ka for the weak acid HA. (c) Calculate the pH at the equivalence point. (d) Select an appropriate indicator for this titration from the table below and justify your answer.