5th vs fifth

5th is not a noun while fifth is a noun.

Word	Noun	Adjective	Verb	Adverb
5th	No	Yes	No	No
fifth	Yes	Yes	No	No

As adjectives, 5th and fifth are synonyms defined as:

5th and fifth: coming next after the fourth and just before the sixth in position

5th (noun)	fifth (noun)
	the musical interval between one note and another five notes away from it
	one part in five equal parts
	a quantity of liquor equal to one fifth of a United States gallon
	position five in a countable series of things

5th (adjective)	fifth (adjective)
coming next after the fourth and just before the sixth in position	coming next after the fourth and just before the sixth in position