# Chemical Forums

## Chemistry Forums for Students => High School Chemistry Forum => Topic started by: sharbeldam on October 01, 2020, 06:48:46 AM

Title: eudiometer problem?
Post by: sharbeldam on October 01, 2020, 06:48:46 AM
In lab, students collect 42.6mL of N2 gas over water 24 C and 751 torr. The water in the eudiometer is 16.5 cm higher than the water outside.
Calculate the dry standard volume of N2

"  The water in the eudiometer is 16.5 cm higher than the water outside. "
this sentence brings all the confusion, does someone has a picture that explains it? does it mean that the atmospheric pressure is higher by 16.5cm water, then i convert that to mmHg.
hence
PN2=Patm-P(difference)-Pwater

and then
PV=nRT
V=nRT/P

but still i have no moles, any hints?
Title: Re: eudiometer problem?
Post by: chenbeier on October 01, 2020, 07:32:55 AM
Eudiometer is a measured tube, what contain water and it is inserted in a vessel of water, see pictures in link. Gas is pushed in through a narrow tube, the water goes out according pressure outside seen on the hight.

https://en.m.wikipedia.org/wiki/Eudiometer

You can calculate the moles. You have given volume, temperature and pressure.
n = pV/RT

You have the hight of the water, what gives the pressure from outside. If both pressures equal then there is no hght. Water levels outside and inside the same.

Check

https://en.m.wikipedia.org/wiki/Centimetre_of_water

Title: Re: eudiometer problem?
Post by: sharbeldam on October 01, 2020, 11:22:19 AM
Isnâ€™t that the volume with water vapor tho? Since they are asking about the dry volume of nitrogen