# chem

posted by .

hi can anyone help

how do i determine the molecular formular of the oxide of arsenic in its in its gaseous state

the answer i got was 17.8 gl -1
for the density,

which law do i use is it boyles law or charles law

thanks

A mol of a gas occupies 22.4 L at STP. If it is 17.8 g/L at STP, then.

molar mass = 17.8 g/L x 22.4 L/mol = ??

If it isn't at STP, then change it to STP using PV = nRT.

where do you get the figure 22.4 as i have tried to figure it out

That is the volume occupied by a mole of any gas at STP. Most of us have that memorized; however, it can be calculated from PV=nRT.
STP is 1 atm (that goes for P), V is what you solve for, place 1 for n (# mols), R is 0.08206 (a constant) and T is 273.15 Kelvin (the T in STP). V will calculate to be 22.414

There may be an easier way to solve for the molecular formula. Why don't you post the entire problem?

thank you for that
i set it out like this

v = 1 x 0.08206 x 273.15
v = 22.414689
v = 22.41

what is the symbol at the end is it g as im not to sure