Answer:
V = 552 mL or 0.552 L
Explanation:
First, we need to calculate the number of moles of H2 using the ideal gas equation which is:
PV = nRT
Solving for n:
n = PV / RT
Where:
P = Pressure
V = Volume
R = Gas constant (0.082 L atm / K mol)
T = Temperature in K
Let's convert first both pressure in atm, remember that 1 atm = 760 mmHg
P = 735 / 760 = 0.967 atm
Pwater = 21 / 760 = 0.028 atm
Finally temperature to Kelvin:
T = 23 + 273.15 = 296.15 K
Now, at first the hydrogen was collected by water displacement so pressure is:
P = 0.967 - 0.028 = 0.939 atm
Now the moles of hydrogen:
n = 0.939 * 0.568 / 0.082 * 296.15
n = 0.022 moles
Now that we have the moles, let's calculate the volume when the pressure is 735 mmHg
V = nRT/P
V = 0.022 * 0.082 * 296.15 / 0.967
V = 0.552 L or 552 mL
This is the volume that hydrogen occupies.
