Question

For a 5.0 g sample of CoCl3·9H2O, what weight of water (in grams) will be lost if the sample is heated to constant weight (all water driven off)?

Answer 1

Here is a worked example of a stoichiometry problem. Just follow the steps.
http://www.jiskha.com/science/chemistry/stoichiometry.html

There is an easier way to do it. Calculate the percent water in CoCl3.9H2O, then (%H2O/100)*5.00 g = mass H2O lost.