For the following reaction:

Question

6ClO2 (g) + 3H2O (l) = 5HClO3 (l) + HCl (g)

If a chemist wants to make 55.0 g of HCl, how much ClO2 is needed?

Answer 1

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