[unleash10]

What happens to the mass of a gas in a vacuum?

[Mitch]

mass is constant.

[unleash10]

So is this a trick question?

a sample of pure octane whose density is .7036 g/ml at 20 C weighs 35.4620g in air at 20 C. What is the mass of the sample in vacuum.

[Borek]

Mass is the same, but results of weighting can be different. It depends on the density of sample and density of weights used. That's effect of Archimedes law - every immersed body 'looses' mass that it displaced. If the previous weighting was done in air, difference is small, but measurable, somewhere below 0.1% IIRC.

[mithrilhack]

how can it be a vaccuum if it has gas?

[Borek]

At this density octane is not a gas, it must be a liquid. So I assume the question is about weightling liquid - once in air, and once i vaccum.

[Kate]

I have a similar problem. I know that at 20,5 ºC the water's density is 1019 kg/m³ and I have 49,7118 g of water at a pressure of 1023 hPa. I want to correct this value - 49,7118 g - to vacuum. How do I do that ?

[billnotgatez]

sometimes I wonder - this is not an answer - just an observation

from the dictionary

vacuum
1. a space entirely devoid of matter. 
2. an enclosed space from which matter, esp. air, has been partially removed so that the matter or gas remaining in the space exerts less pressure than the atmosphere (opposed to plenum). 
3. the state or degree of exhaustion in such an enclosed space. 
4. a space not filled or occupied; emptiness; void: The loss left a vacuum in his heart. 
5. a vacuum cleaner or sweeper. 
6. Physics. a state of lowest energy in a quantum field theory. 
7. of, pertaining to, employing, or producing a vacuum. 
8. (of a hollow container) partly exhausted of gas or air. 
9. pertaining to a device or process that makes use of a vacuum to accomplish a desired task. 
10. noting or pertaining to canning or packaging in which air is removed from the container to prevent deterioration of the contents. 
11. to use a vacuum cleaner on; clean with a vacuum cleaner: to vacuum rugs. 
12. to treat with any vacuum device, as a vacuum drier. 
13. to use a vacuum cleaner: to vacuum in the dining room. 

[Borek]

I have a similar problem. I know that at 20,5 ºC the water's density is 1019 kg/m³ and I have 49,7118 g of water at a pressure of 1023 hPa. I want to correct this value - 49,7118 g - to vacuum. How do I do that ?

What is mass of displaced air?