dry gaseous hcl contained in volume of 1L at STP is dissolved in 200ml of 0.5M barium hydroxide soltion. How many mol of 0.5M hcl would be needed to neutralise the resulting solution?

Answer 1

Ba(OH)2 + 2HCl ==> BaCl2 + 2H2O
mols Ba(OH)2 = M x L = ?
mols HCl = twice that.

Answer 2

how many moles total does it take to neutralize the Ba(OH)2?

moles= 2*.2*.5=.2moles HCl

next, how much did was added as a gas?
moles= 1/22.4

How many moles do you need still?
.2-1/22.4

finally,
.2-1/22.4=.5*litersHCl
solve for the volume of .5M HCl.