Question

How many H2O molecules are contained in 0.0016 moles of the hydrate Na2B4O7.10H2O?

Answer 1

the 10 in front of the H2O in the formula tells us that each molecule of Na2B4O7.10H2O has 10 molecules of H2O

0.0016 moles of Na2B4O7.10H2O is equivalent to (0.0016)*(6.022*10^23) molecules of Na2B4O7.10H2O

so our total number of H2O molecules is

10*(0.0016)*(6.022*10^23)

does that make sense?