AS.030.205 Chapter Notes - Chapter 2: Buffer Solution, Boron, Electronegativity

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3 Jul 2018

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Chapter 2: Acids and Bases: Central to Understanding Organic

Chemistry

2.1: An Introduction to Acids and Bases

Acid (Brønsted – Lowry): a species that loses a proton

Base (Brønsted – Lowry): a species that gains a proton

Acid-base reaction (proton transfer reaction): reaction of acid with base (the

reverse reaction is called the same thing)

*According to Brønsted – Lowry definitions, any species that has a hydrogen can

potentially act as an acid, and any species that has a lone pair can potentially

act as a base

*both an acid and a base must be present in an acid-base reaction b/c an acid cannot

lose a proton unless a base is present to accept it

Reversible/Irreversible Reactions:

*most acid-base reactions are reversible

Conjugate base: the resulting species when an acid loses a proton

Conjugate acid: the resulting species when a base gains a proton

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Acidity: measure of the tendency of a compound to lose a proton

Basicity: measure of a compound’s affinity for a proton

Strong acid/base: strong tendency/high affinity to lose/for a proton

Weak acid/base: little tendency/low affinity to lose/for a proton

*the stronger the acid, the weaker its conjugate base, and the stronger the base, the

weaker its conjugate acid

*HBr is a stronger acid than HCl, so Br- is a weaker base than Cl-

2.2: pKa and pH

*when a strong acid is dissolved in water, almost all the molecules dissociate, so

products are favored at equilibrium (equilibrium lies to the right)

*when a much weaker acid is dissolved in water, very few molecules dissociate, so

reactants are favored at equilibrium (equilibrium lies to the left)

*longer arrow is drawn towards the species favored at equilibrium

Keq (equilibrium constant): degree to which an acid (HA) dissociates in an aqueous

solution

Ka (acid dissociation constant): degree to which an acid (HA) dissociates

pKa: indicator of acid strength (larger Ka = stronger acid, smaller pKa = stronger

acid)

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pH: indicator of concentration of protons in a solution

*do NOT confuse pH and pKa: pH describes acidity of a solution, pKa

indicates tendency of a compound to lose its proton (pKa is a

characteristic)

2.3: Organic Acids and Bases

Carboxylic acids: compounds that have a COOH group

*pKa values range from about 3 to 5 (weak acids)

Alcohols: compounds that have an OH group

* pKa values close to 16 (much weaker acids than carboxylic acids)

Amines: compounds that result from replacing one or more of the hydrogens

bonded to ammonia with a carbon-containing substituent

*amines and ammonia have such high pKa values that they rarely behave as acids –

they are more likely to act as bases (they the most common organic bases)

Protonated Compounds: compounds that gained an additional proton

*based on their pKa values, protonated methylamine is a stronger acid than

protonated ethylamine, which means that methylamine is a weaker base

than ethylamine

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Document Summary

Chapter 2: acids and bases: central to understanding organic. Acid (br nsted lowry): a species that loses a proton. Base (br nsted lowry): a species that gains a proton. Acid-base reaction (proton transfer reaction): reaction of acid with base (the reverse reaction is called the same thing) *according to br nsted lowry definitions, any species that has a hydrogen can potentially act as an acid, and any species that has a lone pair can potentially act as a base. *both an acid and a base must be present in an acid-base reaction b/c an acid cannot lose a proton unless a base is present to accept it. Conjugate base: the resulting species when an acid loses a proton. Conjugate acid: the resulting species when a base gains a proton. Acidity: measure of the tendency of a compound to lose a proton. Basicity: measure of a compound"s affinity for a proton. Strong acid/base: strong tendency/high affinity to lose/for a proton.

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AS.030.205 Chapter Notes - Chapter 2: Buffer Solution, Boron, Electronegativity

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