Unit 2: Acids and Bases in Organic Chemistry
The one skill that predicts almost every reaction to come: finding the acid, finding the base, and reading pKa to see which way it goes.
5 topics · 16 questions
Each topic is a path, not a menu: work down it in order and every question builds on the one above. Click any of them to watch the answer draw itself.
Bronsted-Lowry Acids and Bases
- How it worksHow does a proton transfer from a Bronsted acid to a Bronsted base, shown with curved arrows?
- Worked exampleWalk me through identifying the acid, the base, and both conjugates when acetic acid reacts with ammonia.
- Common mistakeWhy isn't a conjugate base automatically weak just because the acid it came from was strong?
Your turn1 of 2
Acetic acid, CH3COOH, reacts with ammonia, NH3. Which species is the Bronsted acid, and what is its conjugate base?Lewis Acids and Bases
- How it worksHow does an empty orbital on boron accept a lone pair from ammonia to form a brand new bond?
- Worked exampleWalk me through the Lewis acid-base reaction between BF3 and NH3, showing the new bond forming.
- Going furtherWhat happens to the definition of acid and base once a proton is no longer required to be involved?
Your turn1 of 2
In the reaction between BF3 and NH3, boron trifluoride has an empty p orbital and ammonia has a lone pair on nitrogen. What happens when they react as a Lewis acid and a Lewis base?pKa and Predicting the Position of Equilibrium
- How it worksHow does comparing the pKa of an acid against the conjugate acid of a base tell you where equilibrium sits?
- Worked exampleFind which side an equilibrium favors when acetic acid, pKa 4.8, reacts with ethoxide, conjugate acid pKa 16.
- Worked exampleFind the ratio of conjugate base to acid for a compound with pKa 5 dissolved in a solution at pH 7.
- Common mistakeWhy doesn't a reaction stop completely just because its equilibrium favors the starting materials?
Your turn1 of 2
A weak acid has a pKa of 6. It is dissolved in a buffer at pH 8. What is the ratio of conjugate base concentration to acid concentration, [A-]/[HA]?Factors That Control Acidity
- How it worksHow does resonance spreading the negative charge over two oxygens stabilize the acetate conjugate base?
- How it worksHow do the size and electronegativity of the atom holding a negative charge change how acidic a proton is?
- Worked exampleWalk me through ranking ethanol, phenol, and acetic acid from weakest acid to strongest.
Your turn1 of 2
Rank ethanol, phenol, and acetic acid from weakest acid to strongest.Acid-Base Reactions as Curved-Arrow Mechanisms
- How it worksHow does one curved arrow starting on a lone pair and landing on a proton represent an entire acid-base step?
- Worked exampleWalk me through the full curved-arrow mechanism for hydroxide deprotonating acetic acid.
- Ties togetherHow does this same acid-base arrow reappear inside nearly every mechanism later in the course?
Your turn1 of 2
In the curved-arrow mechanism for hydroxide deprotonating acetic acid, two arrows are drawn. What does each arrow represent?