Quick question on chemistry notation (mol fraction vs %)

In summary, the conversation discusses the composition of a gas mixture, specifically the ratio of moles of oxygen to moles of other gases in the mixture. The first paper expresses this as Ar/25%O2, implying that 25% of the gas is oxygen. The second paper expresses it as 0.02 mol frac O2 for a Ar/CO2 atmosphere, and the question is raised of how to write this in the form Ar/X%CO2. The molar fraction is defined as the ratio of moles to moles, and can be converted to a percentage by multiplying by 100. However, it is noted that the composition of the gas mix is ambiguous and can be expressed in different ways, such as
  • #1
rwooduk
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Please post this type of questions in HW section using the template.
Hi,

I have a paper that for a gas mixture writes Ar/25%O2 implying that 25% of the atmosphere of the gas is oxygen.

I have another paper that writes 0.02 mol frac O2 for a Ar/CO2 atmosphere.

Please could someone tell me how I would write the 0.02 mol frac O2 in the form Ar/X%CO2 and what X would be and how you got it?

Thanks in advance for any help!
 
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  • #2
How is the molar fraction defined?
 
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  • #3
Borek said:
How is the molar fraction defined?

hmm molar fraction is ratio of moles to moles, and to get fraction to percent you would multiply by 100, wow that was easy, sorry, thanks for the direction!
 
  • #4
Just remember composition of the gas mix - as listed - is ambiguous. 25% O2 can be v/v (more or less equivalent to molar fraction) or w/w (substantially different).
 
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  • #5
Borek said:
Just remember composition of the gas mix - as listed - is ambiguous. 25% O2 can be v/v (more or less equivalent to molar fraction) or w/w (substantially different).

hmm isn't it exactly equivalent through PV = nRT ?
 
  • #6
rwooduk said:
hmm isn't it exactly equivalent through PV = nRT ?

For real gases not so, especially when the ideal gas approximation no longer holds.
 
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  • #7
Borek said:
For real gases not so, especially when the ideal gas approximation no longer holds.

Good point, thanks again.
 

Related to Quick question on chemistry notation (mol fraction vs %)

1. What is the difference between mol fraction and % in chemistry notation?

Mol fraction, also known as mole fraction, is a unitless quantity that represents the ratio of the number of moles of a particular substance to the total number of moles in a solution. On the other hand, % in chemistry notation refers to the percentage by mass of a particular substance in a solution. In other words, mol fraction is a relative measure, while % is an absolute measure.

2. How do you calculate mol fraction and % in chemistry notation?

To calculate mol fraction, you divide the number of moles of a particular substance by the total number of moles in the solution. For example, if a solution contains 2 moles of substance A and 3 moles of substance B, the mol fraction of substance A would be 2/(2+3) = 0.4. To calculate %, you divide the mass of the particular substance by the total mass of the solution and multiply by 100. For instance, if a solution contains 20 grams of substance A and 80 grams of substance B, the % of substance A would be (20/(20+80))x100 = 20%.

3. Which notation should I use, mol fraction or %, for my chemistry calculations?

The notation you should use depends on the type of calculation you are performing. Mol fraction is typically used for calculations involving the ideal gas law, colligative properties, and equilibrium constants. % is commonly used for calculations involving concentration, such as molarity and molality. It is important to check the units and requirements of your specific problem to determine which notation to use.

4. Can mol fraction and % be converted to each other?

Yes, mol fraction and % can be converted to each other using the following formula: mol fraction = %/100. For example, if you have a solution with a % of 30%, the mol fraction would be 30%/100 = 0.3.

5. Are there any limitations to using mol fraction and % in chemistry notation?

While mol fraction and % are commonly used in chemistry, they do have limitations. Mol fraction is not suitable for solutions that contain more than two components, and % can be misleading for solutions that contain non-volatile solutes. Additionally, both notations assume ideal behavior, which may not always be the case in real-life situations.

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