Partial Pressure of O2: 99.3 KPa at 25°C & Water

[fatima_a]

what is the partial pressure of oxygen gas. if it is collected over water at 25 degrees celcius and an atmospheric pressure of 99.3 KPa. answer in mmHg

okay i know the formula for partial pressures is

P total = P O2 + P H2O

but there is no other info given like the volume or anything so i am lost. please answer by tomorrow. and show all the steps. i have a quiz the day after

 

[Redbelly98]

There should be a discussion of how H20 pressure varies with temperature, either in your textbook or class lecture notes. You might try looking up "vapor pressure" or "pressure, vapor" in the index of your textbook.

 

[Blueshift5]

Based on the given information, the partial pressure of oxygen gas can be calculated as follows:

1. Convert the given atmospheric pressure from kPa to mmHg:
99.3 kPa x 7.50062 mmHg/kPa = 744.4 mmHg

2. Use the ideal gas law to calculate the moles of oxygen gas present:
PV = nRT
n = (PV)/(RT)
n = [(744.4 mmHg)(V)]/[(0.08206 L atm/mol K)(298 K)]
where V is the volume of the gas (which is not given but can be assumed to be 1 L for simplicity)

n = 30.20 moles O2

3. Use Dalton's law of partial pressures to calculate the partial pressure of oxygen gas:
P O2 = (n O2)/(n total) x P total
P O2 = (30.20 moles)/(30.20 moles + x moles) x 744.4 mmHg
where x is the number of moles of water vapor present (since the gas is collected over water)

4. Use the fact that the vapor pressure of water at 25°C is 23.76 mmHg to solve for x:
P H2O = (x moles)/(30.20 moles + x moles) x 744.4 mmHg
23.76 mmHg = (x moles)/(30.20 moles + x moles) x 744.4 mmHg
x = 0.261 moles H2O

5. Now that we know the moles of water vapor present, we can calculate the partial pressure of oxygen gas:
P O2 = (30.20 moles)/(30.20 moles + 0.261 moles) x 744.4 mmHg
P O2 = 30.01 moles x 744.4 mmHg
P O2 = 22320.044 mmHg or 22.32 atm (rounded to 2 significant figures)

Therefore, the partial pressure of oxygen gas collected over water at 25°C and an atmospheric pressure of 99.3 kPa is approximately 22.32 atm or 22320.044 mmHg.