Mole percent composition of earths dry atmosphere is 78% N2, 21% O2 and 1.00% Ar.
Using the atmospheric pressure you recorded in the lab during this experiment (757.5 mmHg) and an ambient temperature of 25C, calculate partial pressures of these 3 gases.
PN2 = 0.78*Ptotal
PO2 = 0.21*Ptotal
PAr = 0.01*Ptotal
All partial pressures are at 25 IF the total P you measured (757.5 mm) was at 25C. If not at 25 you need to correct 757.5 mm from room T to 25 C. Use (P1V1/T1) = (P2V2/T2) for that correction.
What is the p total?
757.5 mm Hg if that's what you measured. I saw one of your other questions which Bob Pursley answered about vapor pressure of water and you quoted 757.5 mm Hg for that one too. Don't mix these two problems together. For this problem as you have quoted it here the partial pressure of N2 is 0.78*757.5 = ? mm Hg.
To calculate the partial pressures of N2, O2, and Ar in the earth's dry atmosphere, we need to use the mole percent composition and the total atmospheric pressure. Here are the steps to calculate the partial pressures of each gas:
Step 1: Convert the mole percent composition to decimal form.
Mole percent of N2 = 78% = 0.78
Mole percent of O2 = 21% = 0.21
Mole percent of Ar = 1% = 0.01
Step 2: Calculate the mole fractions of each gas.
Mole fraction (X) of N2 = mole percent (p) of N2 / 100 = 0.78 / 100 = 0.0078
Mole fraction (X) of O2 = mole percent (p) of O2 / 100 = 0.21 / 100 = 0.0021
Mole fraction (X) of Ar = mole percent (p) of Ar / 100 = 0.01 / 100 = 0.0001
Step 3: Calculate the partial pressure of each gas.
Partial pressure (P) of N2 = mole fraction (X) of N2 * Total atmospheric pressure
Partial pressure (P) of N2 = 0.0078 * 757.5 mmHg = 5.913 mmHg
Partial pressure (P) of O2 = mole fraction (X) of O2 * Total atmospheric pressure
Partial pressure (P) of O2 = 0.0021 * 757.5 mmHg = 1.591 mmHg
Partial pressure (P) of Ar = mole fraction (X) of Ar * Total atmospheric pressure
Partial pressure (P) of Ar = 0.0001 * 757.5 mmHg = 0.076 mmHg
Therefore, the partial pressures of N2, O2, and Ar in the earth's dry atmosphere at an ambient temperature of 25°C and a total atmospheric pressure of 757.5 mmHg are approximately:
- N2: 5.913 mmHg
- O2: 1.591 mmHg
- Ar: 0.076 mmHg