A gas occupies a volume of 40 ml at 734.8 mm and 22* C . The gas was collected over water and the water level inside the eudiometer is the same as that outside. What is the volume of dry gas at S.T.P?

You need to use the combined formula: Pressure = P Volume = V Temperature = T

P1*V1/T1 = P2*V2/T2

then cross multiply

To find the volume of the dry gas at standard temperature and pressure (STP), we need to use the ideal gas law equation. The ideal gas law states that PV = nRT, where P is the pressure, V is the volume, n is the number of moles, R is the ideal gas constant, and T is the temperature in Kelvin.

To solve this problem, we will need to convert the given conditions to the appropriate units.

1. Convert the temperature from Celsius to Kelvin:
T(K) = T(C) + 273.15
T(K) = 22 + 273.15 = 295.15 K

2. Convert the pressure from mm to atm:
1 atm = 760 mmHg
P(atm) = P(mmHg) / 760
P(atm) = 734.8 mmHg / 760 = 0.967 atm

Now we have the values needed to solve for the volume of the dry gas at STP.

3. Apply the ideal gas law equation:
PV = nRT

Since the gas was collected over water and the water level inside the eudiometer is the same as that outside, we can assume that the partial pressure of water vapor is equal to the atmospheric pressure at that temperature.

4. Calculate the partial pressure of the water vapor:
P_water = P(atm) - P_gas
P_water = 0.967 atm - 0.967 atm = 0 atm

Therefore, the partial pressure of the dry gas is equal to the total pressure (P(atm)).

5. Rearrange the ideal gas law equation for the volume of the dry gas:
V_gas = nRT / P_gas
V_gas = V_total - V_water

At STP, the volume of water vapor is negligible, so we can assume it is zero.

6. Substitute the values into the equation:
V_gas = (nRT) / P_gas
V_gas = (nRT) / P(atm)
V_gas = (nRT) / (0.967 atm)

The number of moles (n) can be calculated using the ideal gas law equation:

n = PV / RT

7. Substitute the values into the equation:
n = (P_total - P_water) * V_total / (RT)
n = (0.967 atm) * (40 ml) / (0.0821 L.atm/mol.K * 295.15 K)
n = 0.01641 mol

8. Plug the values of n, R, and T back into the volume equation:
V_gas = (nRT) / (0.967 atm)
V_gas = (0.01641 mol) * (0.0821 L.atm/mol.K) * (295.15 K) / (0.967 atm)
V_gas ≈ 0.427 L

Therefore, the volume of the dry gas at STP is approximately 0.427 liters.