Question

What mass of silver nitrate (AgNO3) is required to prepare 400 g of a 3.50% solution of
AgNO3

Answer 1

How many milliliters of a 0.9 molar HCl
solution are needed to react completely with
15 grams of zinc according to the following
equation?
? HCl + ? Zn → ? ZnCl2 + ? H2
Answer in units of m

Answer 2

3.50% AgNO3 means 3.50g AgNO3/100 g soln. You want 400 g; therefore, you will need
3.50g x (400/100) = ?? g AgNO3.

For your second post, this link will work all of your stoichiometry problems. Remember M x L = moles.
http://www.jiskha.com/science/chemistry/stoichiometry.html