Step-by-step explanation:
To find the volume of dry hydrogen gas at STP, we need to use the combined gas law, which relates the pressure, volume, and temperature of a gas.
The combined gas law is given by:
(P1 V1) / (T1) = (P2 V2) / (T2)
where P1, V1, and T1 are the initial pressure, volume, and temperature of the gas, and P2, V2, and T2 are the final pressure, volume, and temperature of the gas.
First, we need to adjust the initial volume of hydrogen to account for the presence of water vapor. The total pressure in the eudiometer is the sum of the pressure of the hydrogen gas and the pressure of the water vapor, which is equal to the partial pressure of water vapor in the air. The partial pressure of water vapor can be found using a vapor pressure table at the given temperature of 21°C, which is 18.7 mmHg.
Thus, the initial pressure of the hydrogen gas is equal to the total pressure minus the partial pressure of water vapor:
P1 = 735 mmHg - 18.7 mmHg = 716.3 mmHg
Now we can plug in the values into the combined gas law and solve for V2, the volume of the dry hydrogen gas at STP:
(P1 V1) / T1 = (P2 V2) / T2
where P2 = 1 atm (at STP) and T2 = 0°C = 273 K
V2 = (P1 V1 T2) / (T1 P2)
V2 = (716.3 mmHg x 35.5 mL x 273 K) / (294 K x 760 mmHg)
V2 = 29.5 mL
Therefore, the volume of dry hydrogen gas at STP is 29.5 mL.