text: an excess of sodium hydroxide is treated with 1.1 l of dry hydrogen chloride gas measured at stp. what is the? an excess of sodium hydroxide is treated with 1.1 l of dry hydrogen chloride gas measured at stp. what is the mass of sodium chloride formed? one mole of an ideal gas occupies a volume of 22.4 liters  at stp.  we can safely assume that hcl gas under stp conditions behaves pretty much like an idea gas, so 1.1 liter of hcl gas contains 1.1/22.4 moles of hcl.  each mole of hcl that reacts with naoh produces one mole of nacl.  because we are told that the naoh is in excess, the amount of nacl formed will be equal to the amount of hcl gas.  in other words, 1.1/22.4 moles of nacl will be formed.  the molecular mass of nacl is 58.44 grams/mole, so the mass of nacl formed will be:  58.44 gm/mol * 1.1/22.4 mol = 2.87 grams.