The mass of chlorine gas is calculated as follows
find the moles HCl , At STP 1moles = 22.4 liters
what about 174 L
moles = 174l x 1mole/22.4L= 7.77 moles
write the equation for reaction
H2 + Cl2 =2HCl
by
use of mole ratio between cl2 to HCl (1:2) the moles of Cl2 =7.77/2 = 3.885 moles
mass is therefore = 3.885 mol x 71 gmol = 275.84 grams