Question

Arrange the following in the order of increasing acidity. List the most acidic last.

CH3OH

CH3CO2H

CH3CH2CH2CH3

If given a table of acids and their pKas, how do you determine which acid is stronger, especially when the table does not have the compounds that are above listed on the table?

Here is a chart of the table given.

HCl pKa= -7. CH3CO2H pKa= 4.8. H2O pKa= 15.7. CH3CH2OH pKa= 16. CHCH pKa= 25. H2 pKa= 35. H2NH pKa= 38. CH2CH2 pKa= 44. CH3H pKa=50

Answer 1

CH₃OH is methanol, containing – OH group

CH₃CO₂H is acetic acid containing –COOH group

CH₃CH₂CH₂CH₃ is butane, which is an alkane

The table does not have the compounds that are above listed, but on the table there are compounds, which have same functional group. For example on the table there is ethanol with pKa = 16

PKa of alcohol group is 16, so pKa of methanol =16

PKa of CH₃H is 50 (given in table) so, pKa of alkanes are 50. PKa of CH₃CH₂CH₂CH₃ is 50

Compound with lower PKa is more acidic. CH₃CO₂H (PKa= 4.8) has lower PKa than CH₃OH and CH₃CH₂CH₂CH₃ , so it is more acidic than CH₃OH and CH₃CH₂CH₂CH₃ and CH₃OH has lower PKa than CH₃CH₂CH₂CH₃ , so it is more acidic than CH₃CH₂CH₂CH₃ .

The order of increasing acidity of compounds is

Least acidic CH₃CH₂CH₂CH₃ < CH₃OH < CH₃CO₂H more acidic