10 Questions
What is the effect of inductive electron withdrawal by the electronegative oxygen on the electron density of the negatively charged oxygen?
It decreases the electron density, thereby stabilizing it and increasing the acidity of the conjugate acid.
How does electron delocalization contribute to the stability of the conjugate base of a carboxylic acid?
It allows the negative charge to be shared by both oxygens, resulting in delocalized electrons and increased stability.
What is the definition of a Lewis acid?
A species that accepts a share in an electron pair.
What is the characteristic of compounds that are classified as Lewis acids?
They have unfilled valence orbitals that can accept a share in an electron pair.
What is the difference between a Lewis base and a nucleophile?
A Lewis base shares its lone pair with a proton, while a nucleophile shares its lone pair with an atom other than a proton.
How does the conjugate base of a carboxylic acid differ from the conjugate base of an alcohol?
The conjugate base of a carboxylic acid has delocalized electrons, while the conjugate base of an alcohol has localized electrons.
What is the significance of electron localization in the conjugate base of an alcohol?
It results in a negative charge that resides on a single oxygen atom, making the conjugate base less stable.
How do the Brønsted-Lowry and Lewis definitions of an acid differ?
The Brønsted-Lowry definition is limited to proton-donating compounds, while the Lewis definition includes all proton-donating compounds and some additional compounds that do not have protons.
What is the term used to describe a compound that shares its lone pair with an atom other than a proton?
Nucleophile.
Why is the conjugate base of a carboxylic acid more stable than the conjugate base of an alcohol?
It is due to the combination of inductive electron withdrawal and electron delocalization, which results in a more stable conjugate base.
Study Notes
Acidity and Basicity
- Acidity is a measure of a compound's tendency to lose a proton, whereas basicity is a measure of a compound's affinity for a proton.
- A strong acid is one that has a strong tendency to lose a proton, and its conjugate base must be weak because it has little affinity for the proton.
- A weak acid has little tendency to lose its proton, indicating that its conjugate base is strong because it has a high affinity for the proton.
Relationship between Acid and Conjugate Base
- The stronger the acid, the weaker its conjugate base.
- The conjugate acid of a base is the species formed when the base accepts a proton.
- The conjugate base of an acid is the species formed when the acid loses a proton.
pKa and pH
- pKa is a measure of the strength of an acid, with lower pKa values indicating stronger acids.
- pH is a measure of the concentration of hydrogen ions in a solution.
- At equilibrium, the rate of the forward reaction is exactly equivalent to the rate of the reverse reaction.
Acid Rain and Heartburn
- Acid rain is caused by the release of sulfuric and nitric acids into the atmosphere, which can damage aquatic life, soil, and buildings.
- Heartburn is caused by the buildup of excessive amounts of stomach acid (primarily HCl), which can be treated by using a mild base to neutralize the excess hydrochloric acid.
Organic Acids and Bases
- Carboxylic acids are weak acids that have a COOH group and pKa values ranging from about 3 to 5.
- Alcohols are much weaker acids than carboxylic acids, with pKa values close to 16.
- Amines and ammonia have high pKa values and are more likely to act as bases than acids.
How the Structure of an Acid Affects its pKa Value
- The electronegativity and size of an atom can affect the stability of its conjugate base.
- The more electronegative the atom, the stronger its acid and the more stable its conjugate base.
- The size of an atom can also affect its stability, with larger atoms being more stable.
How Substituents Affect the Strength of an Acid
- Replacing one of the hydrogens of the CH3 group with a halogen increases the acidity of the compound.
- Inductive electron withdrawal decreases the electron density about the oxygen that bears the negative charge, thereby stabilizing it.
- The effect a substituent has on the acidity of a compound decreases as the distance between the substituent and the acidic proton increases.
Delocalized Electrons
- Electron delocalization occurs when the negative charge is shared by multiple atoms.
- Delocalized electrons can increase the stability of a conjugate base, making its conjugate acid stronger.
Lewis Acids and Bases
- A Lewis acid is a species that accepts a share in an electron pair.
- A Lewis base is a species that donates a share in an electron pair.
- All Brønsted-Lowry acids fit the Lewis definition, but the Lewis definition also includes compounds that do not lose protons.
- Lewis acids are also called electrophiles, and Lewis bases are also called nucleophiles.
Understanding the behavior of water as an acid and a base, and the concepts of acidity and basicity.
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