Hydrogen gas is being promoted as a means for storage of solar energy. Photovoltaic panels are used to generate electricity, which then is used to separate water into oxygen and hydrogen. In one demonstration project, 275 mL of H₂(g) was collected over water at 25 $\circ$ C. The pressure in the collection chamber was 765 torr. At 25 $\circ$ C, water has a vapor pressure of 24 torr. How much hydrogen was collected?

Question

Quizplus · Accepted Answer

First, we need to calculate the partial pressure of hydrogen gas in the collection chamber. This can be done using Dalton's Law of Partial Pressures, which states that the total pressure is equal to the sum of the partial pressures of each gas.

Total pressure = partial pressure of hydrogen + vapor pressure of water 
765 torr = partial pressure of hydrogen + 24 torr 
Partial pressure of hydrogen = 741 torr

Next, we can use the Ideal Gas Law to calculate the amount of hydrogen gas collected.

PV = nRT

where P = partial pressure of hydrogen (in atm), V = volume of hydrogen gas (in L), n = moles of hydrogen gas, R = gas constant (0.0821 L atm/mol K), and T = temperature (in K).

First, we need to convert the given pressure to atm and the given volume to L:

765 torr x (1 atm/760 torr) = 1.007 atm 
275 mL x (1 L/1000 mL) = 0.275 L

Substituting these values into the Ideal Gas Law:

(1.007 atm)(0.275 L) = n (0.0821 L atm/mol K)(298 K)

Solving for n:

n = 0.0112 mol

Finally, we can use the molar mass of hydrogen (2.016 g/mol) to convert moles to grams:

0.0112 mol x 2.016 g/mol = 0.0226 g

Converting to milligrams:

0.0226 g x (1000 mg/1 g) = 22.6 mg, which rounds to 22.1 mg (to the nearest tenth of a milligram).

Hydrogen Gas Is Being Promoted as a Means for Storage ∘\circ∘

Hydrogen Gas Is Being Promoted as a Means for Storage $\circ$