A gaseous compound consists of element X (at. wt. = 12) and element Y (at. wt. = 1). Its empirical formula is XY2 and its density is 1.25 g/L at STP. What is its molecular formula?
2007-08-22 17:08:14 · 4 answers · asked by BioSci 1 in Science & Mathematics ➔ Chemistry
Assume that the gas is ideal. then you can connect L unknown gas with moles of the unknown gas, using the temperature (273k) and the pressure (1 atm) and the ideal gas law. you can make the same connection using the fact that 1 mole of ideal gas at STP occupies 22.4L.
(1.25 g/L X 22.4L)/(12 + 2)=2
So the molecular formula is X2Y4.
2007-08-22 17:20:15 · answer #1 · answered by Anonymous · 0⤊ 0⤋
At STP Temperature = 273 K
density = molecular weight / RT
Molecular weight = density x RT = 1.25 x 0.0821 x 273 = 28 g/mol
Mass of the empirical formula = 12 + 1 + 1 = 14
28 / 14 = 2
The molecular formula is X2Y4
2007-08-22 17:23:48 · answer #2 · answered by Dr.A 7 · 0⤊ 0⤋
I mole of any gas at STP is 22.4 liters, so 1 mole of your mystery gas is 22.4l x 1.25g/l = 28g.
Now divide the molecular weight by the weight of the emperical formule (if there are no mistakes, this should be a whole number or nearly so).
28/(12 + [2 x 1]) = 28/14 = 2 now we know we need twice the emperical formula to give the actual molecular formula.
so your gas formula is X2Y4
2007-08-22 17:20:51 · answer #3 · answered by Flying Dragon 7 · 0⤊ 0⤋
! 1 mole of an ideal gas occupies 22.4 L at STP
22.4 L x 1.25 g/L = 28 g per mole
XY2 = amu 14
X2Y4 = amu 28 or 28 g/mole
2007-08-22 17:24:59 · answer #4 · answered by skipper 7 · 0⤊ 0⤋