Chem 51B - Useful pKa Values

Vocabulary flashcards reviewing useful pKa values and conjugate bases of common acids from Chem 51B.

$$pK_a$$

A quantitative measure of acid strength, where lower or more negative values indicate stronger acids and higher values indicate weaker acids.

Conjugate Base

The chemical species remaining after an acid has donated a proton ($H^+$).

$HI$ (Hydroiodic Acid)

A very strong hydrohalic acid with a $pK_a$ of $-10$, whose conjugate base is iodide ($I^-$).

$HBr$ (Hydrobromic Acid)

A strong hydrohalic acid with a $pK_a$ of $-9$, whose conjugate base is bromide ($Br^-$).

$HCl$ (Hydrochloric Acid)

A strong hydrohalic acid with a $pK_a$ of $-7$, whose conjugate base is chloride ($Cl^-$).

$H_2SO_4$ (Sulfuric Acid)

A strong diprotic mineral acid with a first $pK_a$ of $-5$, whose conjugate base is hydrogen sulfate ($HSO_4^-$).

$H_3O^+$ (Hydronium Ion)

The conjugate acid of water with a $pK_a$ of $0$, whose conjugate base is $H_2O$.

$HF$ (Hydrofluoric Acid)

A weak hydrohalic acid with a $pK_a$ of $3$, whose conjugate base is fluoride ($F^-$).

$H_3CCOOH$ (Acetic Acid)

A carboxylic acid with a $pK_a$ of $5$, whose conjugate base is acetate ($H_3CCOO^-$).

Pyridinium Ion ($C_5H_5NH^+$)

The conjugate acid of pyridine with a $pK_a$ of $5$, whose conjugate base is pyridine ($C_5H_5N$).

$HN_3$ (Hydrazoic Acid)

An acid with a $pK_a$ of $5$, whose conjugate base is azide ($N_3^-$).

$HCN$ (Hydrogen Cyanide)

A weak acid with a $pK_a$ of $9$, whose conjugate base is cyanide ($CN^-$).

Phenol ($PhOH$)

An aromatic alcohol with a $pK_a$ of $10$, whose conjugate base is phenoxide ($PhO^-$).

$Et_3NH^+$ (Triethylammonium Ion)

A protonated tertiary amine with a $pK_a$ of $11$, whose conjugate base is triethylamine ($Et_3N$).

$H_3COH$ (Methanol)

An aliphatic alcohol with a $pK_a$ of $16$, whose conjugate base is methoxide ($H_3CO^-$).

Phenylacetylene ($H-C \equiv C-Ph$)

A terminal alkyne with a $pK_a$ of $25$, whose conjugate base is an acetylide anion ($^-C \equiv C-Ph$).

$NH_3$ (Ammonia)

A very weak acid with a $pK_a$ of $36$, whose conjugate base is the amide ion ($NH_2^-$).

$H_2$ (Hydrogen Gas)

A diatomic molecule acting as an extremely weak acid with a $pK_a$ of $40$, whose conjugate base is hydride ($H^-$).

$CH_4$ (Methane)

An alkane acting as an extremely weak acid with a $pK_a$ of $50$, whose conjugate base is the methanide/methyl carbanion ($CH_3^-$).