A gas is collected over water at 30.0 degrees celsius. It's pressure is 752.5 mm Hg. What is the pressure of the dry gas? Water vapor pressure at twenty degrees Celsius is 27.5 mm Hg.

See your other post. You want to solve for pdry gas.

To find the pressure of the dry gas, you need to subtract the water vapor pressure from the total pressure.

Given:
Temperature of the gas (T) = 30.0 degrees Celsius
Pressure of the gas collected over water (Ptotal) = 752.5 mm Hg
Water vapor pressure at 20 degrees Celsius (Pwater vapor) = 27.5 mm Hg

To convert Celsius to Kelvin, you need to add 273.15 to the temperature:
T in Kelvin = 30.0 + 273.15 = 303.15 K

The total pressure of the dry gas can be found using Dalton's law of partial pressures, which states that the total pressure exerted by a gas mixture is the sum of the pressures of each individual gas in the mixture.

Ptotal = Pdry gas + Pwater vapor

Since we want to find Pdry gas, we rearrange the formula:

Pdry gas = Ptotal - Pwater vapor

Substituting the values:

Pdry gas = 752.5 mm Hg - 27.5 mm Hg = 725 mm Hg

Therefore, the pressure of the dry gas is 725 mm Hg.