A 5.2 molal aqueous solution of methyl alcohol, CH3OH, is supplied. What is the mole fraction of methyl alcohol in the solution?
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Answer: 1.61 x 10⁴ kPa
Dalton's law <u>states that the sum of the partial pressures of each gas equals the total pressure of the gas mixture.</u> According to this law,
Pi = xi P
where Pi is the partial pressure of the gas i, xi is the mole fraction of the gas i in the gas mixture and P is the total pressure.
The mole fraction <u>is defined as the quotient between the moles of solute (ni) and the total moles of the mixture (nt)</u>, which is calculated by adding the moles of all its components:
xi =
In the Trimix 10/50 mix you have 10% oxygen, 50% helium and 40% nitrogen.
To calculate the total number of moles of the mixture and thus determine the molar fraction of helium, we consider 100 g and calculate the number of moles that represent 10 g of O₂ (n₁), 50 g of He (n₂) and 40 g of N₂ (n₃):
n₁ = 10 g x = 0.313 mol
n₂ = 50 g x = 6.246 mol
n₃ = 40 g x = 1.428 mol
Then the total number of moles (nt) will be:
nt = n₁ + n₂ + n₃ = 0.313 mol + 6.246 mol +1.428 mol
nt = 7,987 mol
Then, the mole fraction of helium (x₂) in the mixture will be,
x₂ = = 0.78
and the partial pressure of helium in the mixture, according to Dalton's law, will be:
P₂ = x₂ P = 0.78 x 2.07 x 10⁴ kPa
P₂= 1.61 x 10⁴ kPa
So, <u>the partial pressure of helium if a tank of trimix 10/50 has a total pressure of 2.07 x 104 kPa is 1.61 x 10⁴ kPa</u>