1. What do the following phrases have in common?

In a class by itself
Aboard the China Clipper
Mormon Tabernacle Choir
Left in a cloud of dust
On a clear day
Farmer's Almanac list of full moon dates

2. What do the following words have in common?

IMP
APE
AWL
AMBLE

HINTS:
1)
#1: The answer is hidden in each phrase.
#2: Salt

2. Each word can be changed into a new one by using the same three letters.

Answer:

1. Each phrase contains the consecutive letters NACL, (NaCl), the chemical formula for sodium chloride (salt). 

2. Each word can be changed into a new one by adding the letters SCR  at the front of the word.

SCRIMP / SCRAPE / SCRAWL / SCRAMBLE