[lmvent]

A sample of zinc metal was reacted with an excess of hydrochloric acid.


Zn(s) + 2HCl(aq) ==> ZnCl2(aq) + H2(g)




All of the zinc reacted, and the hydrogen gas was collected over water at 20oC; the barometric pressure was 752 mmHg. The apparatus was similar to that shown in Figure 5.20, but the level of water inside the tube was 27.0 cm above the level outside the tube. If the volume of gas in the tube is 23.6 mL, how many grams of zinc were there in the sample? Do not enter unit. The density of Hg is 13.596 g/mL and the density of water is 1.000 g/mL.

I can figure out how to do it if the water was lined up, but I don't know how to find the pressure of 27 cm of water. *delete me*

[Borek]

In general - and not very accurately - 10 meters of water is 1 atm.

Think about the pressure definition. Imagine cuboid of water of known sizes. It has an easy to calculate mass (you will need water density for that). Now take the definition of pressure - you know the mass of cuboid, you know its base surface. That should be enough.

[xiankai]

isnt liquid pressure independant of base area?

[Borek]

isnt liquid pressure independant of base area?

Did I wrote opposite?

[lmvent]

That really doesn't help me all that much...I was looking at the pressure of a liquid=(rho)gh, but when I use that to calculate the pressure of the gas and use the ideal gas law, I get the wrong answer.  This is for an online homework set and it's telling me I got the wrong answer.  I keep getting 0.063 g Zn.  Anybody know what I might be doing wrong?

[Borek]

That really doesn't help me all that much...I was looking at the pressure of a liquid=(rho)gh, but when I use that to calculate the pressure of the gas and use the ideal gas law, I get the wrong answer.

Perhaps you forgot that calculated pressure of water is here only to modify atmospheric pressure?