Calculated the pressure of the alcohol

1. Nov 27, 2007

sun

1. The problem statement, all variables and given/known data
Air is trapped above liquid ethyl alcohol in a rigid container. If the air pressure above the liquid is 1.10atm, determine the pressure inside a bubble 4.0m below the surface of the liquid.

Image: Think of a cylindrical container with a layer of air at the top. The remaining is filled with ethyl alcohol. 4m below the top of the alcohol is a bubble of air.

2. Relevant equations

P=P(atm)+pgh
p(ethyl-OH)=.806X10^3kg/m^3

3. The attempt at a solution

So i calculated the pressure of the alcohol 4m below the surface and got 1.3X10^5Pa. However, i'm not sure what to do in order to get the pressure in the bubble.
Suggestions would be appreciated.

thanks

Last edited: Nov 28, 2007
2. Nov 27, 2007

Gokul43201

Staff Emeritus
How did you go from a density of 0.8X10^3 to a pressure of 1.3X10^5? What units are all these quantities in?

3. Nov 28, 2007

sun

This is what i did in order to get the pressure of the ethyl 4m down:

P=1.01310^5Pa+(.806X10^-3kg/m^3)(9.8m/s^s)(4m)=1.33X10^5Pa

4. Nov 28, 2007

Gokul43201

Staff Emeritus
Looks okay so far.

Now, since they don't tell you the size of the bubble, you are probably expected to assume that the pressure inside the bubble is equal to the pressure of the liquid around it. So you've got the answer you need.