# Need help calculating number of moles

• Jordan Michaels
In summary, the conversation involves solving for the pressure, number of moles and molecules, and diameter of a bubble rising from the bottom of a lake to the surface. The pressure at the bottom is calculated using the ideal gas law and the pressure at the surface is found to be 885300 Pascals. The diameter of the bubble at the surface is 2.09 mm. The problem of finding the number of moles and molecules in the bubble is discussed, with the suggestion to use the ideal gas law and make assumptions about the gas inside the bubble. It is noted that the gas may deviate from ideal gas behavior at high pressure and low temperature, but the compressibility factor is still relatively close to 1.
Jordan Michaels

## Homework Statement

A bubble rises from the bottom of a lake of depth 80.0 m, where the temperature is 4oC. The water temperature at the surface is 18oC. Assume the bubble to be in spherical shape and has an initial diameter of 1.00 mm. Assume that the pressure at the surface of the lake is 1.0 atm. Calculate a) the pressure at the bottom b) the number of moles and molecules in the bubble and c) the diameter of the bubble at the surface.

## Homework Equations

PV=nRT
P(bottom) = P(atm) + d(ro)*g*h

## The Attempt at a Solution

I have solved part a and c but I cannot answer part b. The answer to part a is 885300 Pascals and the answer to part c is 2.09 mm but no mater what I try I cannot get the correct answer to past b.

Hi Jordan
Sorry - I answered the wrong question, so I erased it.

Problem b: I think you need to make an assumption about what the stuff in the bubble is. Do you have a guess? Also, you will need to use the Ideal Gas Law. Do you know what that is?

Regards,
Buzz

Last edited:
using
PV=nRT
did you get 2.01*10^-7mol
Note that the gas in the bubble is deviating significantly from an ideal gas under such high pressure and low temperature

Buzz Bloom said:
I think you need to make an assumption about what the stuff in the bubble is.
Are you sure?

Buzz Bloom
Trollfaz said:
using
PV=nRT
did you get 2.01*10^-7mol
Note that the gas in the bubble is deviating significantly from an ideal gas under such high pressure and low temperature
Air at about 9 bars and 4 C does not deviate much from ideal gas behavior. What is your estimate of the compressibility factor Z at these conditions? I guess it all boils down to what one considers "significantly."

haruspex said:
Are you sure?
Hi haruspex:

Thanks for the question. My mistake was thinking about determining the mass of the bubble rather than the moles.

Regards,
Buzz

## 1. What is a mole?

A mole is a unit of measurement in chemistry that represents the amount of a substance. It is equal to the Avogadro's number, which is approximately 6.02 x 10^23 particles.

## 2. How do I calculate the number of moles?

To calculate the number of moles, you need to know the mass of the substance and its molar mass. Then, divide the mass by the molar mass to get the number of moles. The formula is: moles = mass (g) / molar mass (g/mol).

## 3. What is molar mass?

Molar mass is the mass of one mole of a substance. It is expressed in grams per mole (g/mol) and can be found by adding the atomic mass of each element in a compound.

## 4. Can I use the periodic table to calculate the molar mass?

Yes, the periodic table provides the atomic mass of each element, which can be used to calculate the molar mass of a compound.

## 5. Why do we need to calculate the number of moles?

Calculating the number of moles allows us to accurately measure and compare the amount of different substances in a chemical reaction. It also helps us determine the mass of a substance needed for a reaction or the amount of product produced.

• Introductory Physics Homework Help
Replies
7
Views
953
• Introductory Physics Homework Help
Replies
5
Views
3K
• Introductory Physics Homework Help
Replies
2
Views
2K
• Introductory Physics Homework Help
Replies
5
Views
4K
• Introductory Physics Homework Help
Replies
3
Views
7K
• Introductory Physics Homework Help
Replies
3
Views
3K
• Introductory Physics Homework Help
Replies
3
Views
1K
• Introductory Physics Homework Help
Replies
5
Views
2K
• Introductory Physics Homework Help
Replies
8
Views
1K
• Introductory Physics Homework Help
Replies
2
Views
3K