Ch. 3 - Acids and BasesWorksheetSee all chapters
All Chapters
Ch. 1 - A Review of General Chemistry
Ch. 2 - Molecular Representations
Ch. 3 - Acids and Bases
Ch. 4 - Alkanes and Cycloalkanes
Ch. 5 - Chirality
Ch. 6 - Thermodynamics and Kinetics
Ch. 7 - Substitution Reactions
Ch. 8 - Elimination Reactions
Ch. 9 - Alkenes and Alkynes
Ch. 10 - Addition Reactions
Ch. 11 - Radical Reactions
Ch. 12 - Alcohols, Ethers, Epoxides and Thiols
Ch. 13 - Alcohols and Carbonyl Compounds
Ch. 14 - Synthetic Techniques
Ch. 15 - Analytical Techniques: IR, NMR, Mass Spect
Ch. 16 - Conjugated Systems
Ch. 17 - Aromaticity
Ch. 18 - Reactions of Aromatics: EAS and Beyond
Ch. 19 - Aldehydes and Ketones: Nucleophilic Addition
Ch. 20 - Carboxylic Acid Derivatives: NAS
Ch. 21 - Enolate Chemistry: Reactions at the Alpha-Carbon
Ch. 22 - Condensation Chemistry
Ch. 23 - Amines
Ch. 24 - Carbohydrates
Ch. 25 - Phenols
Ch. 26 - Amino Acids, Peptides, and Proteins

Now that we understand what an acid is, we need a method of quantifying which acids are stronger and which are weaker. pH doesn’t work for this, let me explain why:

pH vs. pKa

Concept #1: Why we use pKa instead of pH. 

The Ka (dissociation constant) describes the tendency of a molecule to break apart. In the case of acids, that specifically means donating protons, which is exactly what we are interested in knowing!

Concept #2: The relationship between equilibrium constant and pKa.   

Concept #3: The pH scale vs. the pKa scale.

The pH and pKa scales really are completely different. Pardon my French! pKas are obviously something I’m really passionate about. 

Calculating pKa

This is the easiest kind of question you could get. Calculating pKa’s just takes some very simple math. 

What is the pKa of acetic acid? Hint: take the negative log of the dissociation constant.

Example #1: Calculate the pKa of acetic acid. 

What is the pKa of ammonium? Hint: take the negative log of the dissociation constant.

Example #2: Calculate the pKa of ammonium and determine if it is a stronger acid than acetic acid.