Answer: 650 moles
Explanation: so converted in grams just to make it easy for me, its 5850 g of water right, which is 325 moles of water 
so here's the balanced equation 
MgCl2 + H20 ==> 2HCl + MgO 
thus 1 mole of h20 gives us 2 moles of hcl, so 325 x 2 = 650 moles of hcl