# Calculating Mole Fractions of N2 and O2 Dissolved in Water Using Henry's Law?

• Chemistry
• Blitzy89
In summary, the conversation discusses the calculation of mole fractions of N2 and O2 dissolved in water using Henry's law and Raoult's law. The Henry's law constants for N2 and O2 are given and the molar fractions for the two gases in dry air are also provided. There may be potential errors in the calculations, such as not accounting for the molar fraction of water in the solution.
Blitzy89

## Homework Statement

We know that for dry air, we have:
-78.08% mol N2 ;
-20.94% mol O2.
This is:
- Y(N2) = 0.7808 for nitrogen (the molar fraction in vapor)
- Y (O2) = 0.2094 for oxygen

Knowing that the Henry's law constants are:
for N2 and O2 are 6.51 x 10^7 Torr and 3.3 x 10^7 Torr, respectively

Calculate the mole fractions of N2 and O2 dissolved in water (xN2 and xO2) under total pressure of 1.000 bar

## Homework Equations

Henry's law:
The partial pressure = henry's constant k1 x mole fraction of water (x)
P(N2) = K(N2).X(N2)
Same for O2.

Also, from Raoult's law:
Y(N2) = P(N2)/P(tot)
Same for oxygen.

## The Attempt at a Solution

I tried applying the equations, but instead of the expected (x(N2)=0.6), I get really small results such as 0.00000651

I am just wondering if I am doing anything wrong by mixing the vapour molar fraction equation with Henry's law for the molar fractions for water?

Thank you.

For some reasons I have troubles following what you did and I can't get the picture. But, there are things that are potentially wrong:

Blitzy89 said:
Knowing that the Henry's law constants are:
for N2 and O2 are 6.51 x 10^7 Torr and 3.3 x 10^7 Torr, respectively

Henry's law constant is usually listed in pressure/concentration units, these constants have only pressure. What happened to concentration?

And, if the answer is "molar fraction is considered unitless", is it molar fraction of gas in the solution? And if so,

expected (x(N2)=0.6)

what about water, which should have molar fraction well over 0.9?

Borek said:
what about water, which should have molar fraction well over 0.9?

Thank you for the tip, this is what I hadn't thought about.
It works out after you include the water.

## 1. What is Henry's law?

Henry's law is a gas law that states the amount of gas dissolved in a liquid is directly proportional to the partial pressure of that gas above the liquid.

## 2. How is Henry's law expressed mathematically?

Henry's law is expressed as C = kP, where C is the concentration of the gas in moles per liter, k is the Henry's law constant, and P is the partial pressure of the gas in atmospheres.

## 3. What is the significance of mole fractions in Henry's law?

Mole fractions represent the proportion of a gas in a mixture, and in Henry's law, they are used to calculate the concentration of the gas in a liquid. The mole fraction of a gas is equal to its partial pressure divided by the total pressure of the gas mixture.

## 4. How is Henry's law used in real-world applications?

Henry's law is used in various industries, such as in the production of carbonated drinks, where the solubility of carbon dioxide in water is important. It is also used in environmental science to determine the solubility of gases in bodies of water, and in chemistry for gas-liquid reactions.

## 5. What factors can affect the accuracy of Henry's law?

The accuracy of Henry's law can be affected by factors such as temperature, pressure, and the nature of the gas and liquid involved. Additionally, the presence of other dissolved substances in the liquid can also impact the solubility of gases and therefore affect the accuracy of Henry's law calculations.

• Biology and Chemistry Homework Help
Replies
6
Views
2K
• Biology and Chemistry Homework Help
Replies
3
Views
2K
• Biology and Chemistry Homework Help
Replies
5
Views
1K
• Biology and Chemistry Homework Help
Replies
1
Views
5K
• Biology and Chemistry Homework Help
Replies
1
Views
3K
• Biology and Chemistry Homework Help
Replies
8
Views
16K
• Biology and Chemistry Homework Help
Replies
1
Views
8K
• Biology and Chemistry Homework Help
Replies
4
Views
4K
• Introductory Physics Homework Help
Replies
8
Views
6K
• Biology and Chemistry Homework Help
Replies
4
Views
4K