What is the Mass Density of Air at 1 atm and -50°C?

AI Thread Summary
The discussion focuses on calculating the mass density of air at 1 atm and -50°C, noting that the average molecular mass of air is 29 u. The initial calculations yield an incorrect density result, prompting a request for assistance. Participants emphasize the importance of correctly carrying units through the equations and understanding the relationship between molecular mass, mass, and density. Clarification is sought on converting molecular mass into a usable format for density calculations. Accurate density values for air at the specified conditions are expected to be around 1 to 3 kg/m³.
jmb07
Messages
27
Reaction score
0
Average molecular mass of air is 29 u. What is the mass density of air at 1 atm and -50 degrees celsius??

This is what i have so far...

V=(NkT)/P so V= [(29u)(1.38E^-23)(-50 + 273)]/ 1 = 8.9 x10^-20

The mass is equal to 29u x (6.022 x 10^23) =1.75 x 10^25

density =m/v so = 1.96 x 10^44...and that is wayyyy off! The correct answer is like around 1, 2, or 3...i need some help. What am i doing wrong?
 
Physics news on Phys.org
Try carrying your units through your equations. What does it mean to have a molecular mass of 29?
 
uh...i know i could try to convert the 29u to (number of atoms)...but i don't have any molecular weight
 
29u tells you something about the relationship between mass (which is connected to density) and the number of moles (which is connected to the ideal gas law that you're using).
 
TL;DR Summary: I came across this question from a Sri Lankan A-level textbook. Question - An ice cube with a length of 10 cm is immersed in water at 0 °C. An observer observes the ice cube from the water, and it seems to be 7.75 cm long. If the refractive index of water is 4/3, find the height of the ice cube immersed in the water. I could not understand how the apparent height of the ice cube in the water depends on the height of the ice cube immersed in the water. Does anyone have an...
Thread 'Variable mass system : water sprayed into a moving container'
Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...
Back
Top