Question

A student designs an ammeter (a device that measures electrical current) that is based on the electrolysis of water into hydrogen and oxygen gases. When electrical current of unknown magnitude is run through the device for 2.00 min , 12.4 mL of water-saturated H2(g) is collected. The temperature and pressure of the system are 25 ∘C and 715 torr. Part A How many moles of hydrogen gas are produced? Express your answer to three significant figures and include the appropriate units.

Answer 1

Answer:

4.61 x 10ˉ⁴ mole H₂(g)

Explanation:

Given electric current for 2 min. => 12.4ml of wet H₂(g) at 25⁰C & 715Torr => ? moles H₂(g)

PV = nRT => n = PV/RT

• P = P(H₂) + P(H₂O) = 715Torr = 715mm = P(H₂) + 23.8mm  

     => P(H₂) = (715 – 23.8)mm = 619.2mm = 619.2mm/760mm/Atm = 0.815Atm

• V = 12.8ml = 0.0128L

• R = 0.08206 L∙Atm/mol∙K  

• T = 25⁰C = 298K

Substituting …  n = PV/RT

=>  n = (0.815Atm)(0.0128L)/(0.08206 L∙Atm/mol∙K)(298K) = 4.61 x 10ˉ⁴ mole H₂(g)