200 ml of oxygen is collected over water at 18 degree Celsius and standard pressure, what will the volume of the dry oxygen be at STP?

Look up vapor pressure of H2O at 18 C. Call that vp

Use (P1V1/T1) = (P2V2/T2)
P1 = 760-vp
V1 = 200 mL
T1 = 273 + 18
P2 = 760
V2 = ?
T2 = 273
Substitute and solve for V2.

To find the volume of dry oxygen at STP (Standard Temperature and Pressure), we need to correct for the presence of water vapor.

Step 1: Calculate the vapor pressure of water at 18 degrees Celsius.
At 18 degrees Celsius, the vapor pressure of water is 15.5 mmHg.

Step 2: Determine the total pressure.
Since the question specifies that the collection is done at standard pressure, we assume this to be 1 atmosphere or 760 mmHg.

Step 3: Calculate the partial pressure of the oxygen.
The partial pressure of the gas collected (oxygen) is equal to the total pressure minus the vapor pressure of water.
Partial pressure of oxygen = Total pressure - Vapor pressure of water
Partial pressure of oxygen = 760 mmHg - 15.5 mmHg
Partial pressure of oxygen = 744.5 mmHg

Step 4: Apply the ideal gas law to find the volume of dry oxygen.
The ideal gas law is given by the equation:
PV = nRT, where P is the pressure, V is the volume, n is the number of moles of gas, R is the ideal gas constant, and T is the temperature in Kelvin.

We know that the pressure (P) is 744.5 mmHg (converted to atm), and the temperature (T) is 18 degrees Celsius, which needs to be converted to Kelvin.
T(K) = T(C) + 273.15
T(K) = 18 + 273.15
T(K) = 291.15 K

We also know that the volume of the collected oxygen is 200 ml, which needs to be converted to liters.
Volume (V) = 200 ml = 0.2 L

Now we can rearrange the ideal gas law equation to solve for the volume of dry oxygen (V).
V = (nRT) / P

Since we want to find the volume at STP, we need to use the values for STP, which are:
1 atm (or 760 mmHg) for pressure and 273.15 K for temperature.

Now we can plug in all the values into the equation:
V(dry) = (nRT(STP)) / P(dry)

V(dry) = (n * 0.0821 * 273.15) / 1

Simplifying the equation:
V(dry) = 22.414 * n

So, to find the volume of dry oxygen at STP, we need to know the number of moles of oxygen collected.