Acid-base reactions of amines

Question 1

miscible means

Answer 1

a species is capable of mixing

Question 2

the trend for miscibility for the members of the homologous series of primary aliphatic amines is

Answer 2

a decrease in solubility as the carbon chain length increases. the first few members can dissolve in water because they can form hydrogen bonds with the water molecules

Question 3

phenylamine is ………………………. soluble in water

Answer 3

only slightly soluble in H2O

Question 4

amines can also react slightly with water to form…………………..
the equation for the reaction of methylamine and water is:

Answer 4

form alkaline solutions, similar to the reaction of ammonia with water to form an ammonium and hydroxyl ion
CH3NH2 + H2O → CH3NH3+ + OH-

Question 5

when ammonia or an amine react with water, the lone pair of electrons on the N atom forms a ……… bond with the …………………..of a water molecule to form a cation

Answer 5

the lone air of electrons forms a dative covalent bond with the hydrogen from a H2O molecule

Question 6

basicity of a base is

Answer 6

the extent t which it can donate a lone pair of electrons to the hydrogen atom of a water molecule

Question 7

water is equally good as a ……………and as an………

Answer 7

base and acid, which is why its pKa value is 7.00

Question 8

methylamine is a ……………. base than ammonia

Answer 8

stronger, pH 10.64 while NH3 is 9.30

Question 9

the longer the carbon chain length on a primary aliphatic amine, the greater/weaker its basicity

Answer 9

the greater the basicity

Question 10

methylamine is a stronger base than ammonia because

Answer 10

its methyl group is electron releasing and so has an increased electron density on the nitrogen compared with ammonia

Question 11

the equation for the reaction between butylamine with water is

Answer 11

CH3CH2CH2CH2NH2 + H2O → CH3CH2CH2CH2NH3+ + OH-

Question 12

phenylamine has a lower basicity than ammonia and aliphatic amines because

Answer 12

• as with phenol, the lone pair of electron on the nitrogen atom (in phenol these are on the oxygen) are attracted to the delocalised electrons in the pi bond
• this means the N atom is less electron-rich and the lone pair of electrons are less available to donate to the hydrogen atom of a water molecule
• so unlike in ammonia, where the lone pair is more available, and in aliphatic amines where the electron density of the nitrogen atom is further increased by the electron releasing properties of the alkyl groups bonded to the N atom, phenylamine has a much lower pH than ammonia at pH 4.62, so has a lower basicity than water itself

Question 13

all amines react with acids to form

Answer 13

ionic salts

Question 14

the equation for the reaction of methylamine with nitric acid is

Answer 14

CH3NH2 + HNO3 → CH3NH3+ + NO3-