ammonia density....desperate for help

mummyjojo

Density of ammonia at STP= 0.760glitre-1

I need to calculate the density of the ammonia at 25oC and 760mmHg.

I have been given a hint that I need to determine the volume that 1 litre at STP would have at 25oC and 760mmHg.......but this has not helped at all. Im still none the wiser as to what I need to do here.

Could someone please help me with this. Im really useless with chemistry so please make your answer as fool proof as possible (as I truly am that much of a twit )
I would be very very grateful
Kind regards to all who have taken the time to read my message,
J

Hix3r · Regular Joined: 24 Apr 2007 Posts: 43 Location: Hungary

There is a thing which is useful at these time. Called the ideal gas law. This is your friend.

pV = nRT

with this you can exactly tell one cubic metre gas' amount at an exact temperature (in Kelvins!!!) at an exact pressure... WHOA! This is just what we need here don't we?

So we have to put everything in SI. So no Hgmm, we have to calculate it to Pascals.(1 mmHg = 133322 Pa, R=8.31 it's a constant)

0.001*760*133322=x*8.31*298

x=0.001*760*133322/8.31*298

x=40.91 mol/litre

Nice! Now we have to calculate the standard molecular weight of ammonia and then divide that with x. Standard molecular weight of ammonia= 14+3*1=17 g/mol

So 17/40.91= 0.4155 g/litre

WOW, so we got that ammonia at a higher temperature has lower density... Because STP refers to 0°C and 100 kPa, and we have here 25°C and 101 kPa (roughly). Anyway this is not a surprise is it?

How do heat balloons work then? They heat up the air, which then has lower density then the air surrounding the balloon, and the balloon lifts up! Awesome.