Question

How do you find the pressure of a gas in a eudiometer tube?

I really just need someone to tell me the steps because I can't find them. Here's some more information, though: the gas is H_"2", the room temperature is 24.7C, and the barometric pressure is 766 torr. Thanks.

Answer 1

Here's how you can do that.

Explanation:

The idea here is that the gas is being collected over water, which basically means that the tube will contain hydrogen gas and water vapor.

A typical set up involving a eudiometer tube looks like this

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Now, you know the temperature at which the gas is being collected, so you can look up the vapor pressure of water at that temperature. In this case, you have

`P_( "H"_2"O") ~~ "23.56 torr"`

http://www.endmemo.com/chem/vaporpressurewater.php

Now you can use Dalton's Law of Partial Pressures to figure out the partial pressure of hydrogen gas in the mixture.

`color(blue)(ul(color(black)(P_ "total" = P_ ("H"_ 2) + P_ ("H"_ 2"O"))))`

You will have

`P_ ("H"_ 2) = P_"total" - P_ ("H"_ 2"O")`

Keep in mind that the total pressure is simply the barometric pressure, i.e. the pressure of the hydrogen gas + water vapor mixture.