sweetness vs pleasantness

sweetness and pleasantness both are nouns.

Word	Noun	Adjective	Verb	Adverb
sweetness	Yes	No	No	No
pleasantness	Yes	No	No	No

As nouns, sweetness and pleasantness are synonyms defined as:

sweetness (noun)	pleasantness (noun)
the property of tasting as if it contains sugar	the quality of giving pleasure
a pleasingly sweet olfactory property	the feeling caused by agreeable stimuli; one pole of a continuum of states of feeling
the quality of giving pleasure
the taste experience when sugar dissolves in the mouth