calculate the density of helium in a helium balloon at 21.7 degress celsius. (Assume that the pressure inside the balloon is 1.15 atm.)
Why can't you use the same formula I gave you from your earlier post?
P*molar mass = density*R*T
I don't have the molar mass just P, T, and R
I thought the molar mass of He was 4.003. At least it was the last time I looked at the periodic table.
so i get 0.19026 but its wrong did i do something wrong?
No, that's the correct answer. The unit is g/L. Is that the unit you are to report? I worked the problem another way and obtained the same answer. It goes like this.
density He at STP is g/L = 4.0026/22.4 L = 0.1787 g/L x (factor for T) x (factor for P).
factor for T (remembering that density = m/v). If T goes up (from 273 at STP to 294.9) v must increase; therefore, density must decrease so the factor is 273/294.9).
factor for P. If P goes up (from 1 to 1.15), v goes down and density goes up so factor is 1.15/1. Putting that together we have
0.1787 g/L x (273.2/294.9) x (1.15/1) =
0.190 g/L. One other point to check. If you reported your answer as 0.19026 g/L, that's too many significant figures and the data base would tell you it was wrong. 0.190 g/L is what you should report.