Consider the reaction

Mg +2HCl ------>MgCl2 + H2

What is the minimum amount of 1.85M HCl is necessary to produce 28.5L of H2 at STP
Please help me work this problem

1 answer

You know a mole of a gas at STP occupies 22.4 L.
moles H2 produced = 28.5L/22.4 L/mol = ??
Use the coefficients in the balanced equation to convert moles H2 to moles HCl.
Then MHCl = moles HCl/L HCl. You have M HCl and moles HCl, solve for L and convert to mL.