Use Dalton’s law: partial pressure = mole fraction × total pressure
Find the mole fraction: moles of gas ÷ total moles of all gases
Multiply the mole fraction by the total pressure
Use the formula: Pgas = Xgas × Ptotal
If moles are given, calculate total moles first
If volume and temperature are constant, use the ideal gas law: P = nRT/V
For a gas collected over water, subtract water vapor pressure from total pressure
Use units consistently, such as atm, kPa, or mmHg
Check that the partial pressures of all gases add up to the total pressure