A 5.0g sample of Cu(NO3)2•nH2O is heated, and 3.9g of the anhydrous salt remains. what is the value for n?

2.9

Explanation:

Molar mass of Cu(NO3)2 = 187.5 g/mol

Molar mass of water = 18.0 g/mol

%H2O = (5.0 g - 3.9 g) / 5.0 g X 100 (100 is to get percent) = (1.1 g) / 5.0 g X 100

= 22.0 %

% H2O = ( mass of H20 alone) / (mass of total hydrate)

0.22 = 18.0n / (18.0n + 187.5)

n = 2.9 = (about) 3

"record the time to complete a chemical reaction" would most likely be part of a lab procedure.