The vapor pressure of water changes with temperature, as shown here. A student d
ID: 1048610 • Letter: T
Question
The vapor pressure of water changes with temperature, as shown here. 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 2.50 min, 11.9 mL of water-saturated H_2 (g) is collected. The temperature and pressure of the system are 25 degree C and 715 torr. How many moles of hydrogen gas are produced? Express your answer to three significant figures and include the appropriate units.Explanation / Answer
PT = PH2O + PH2
PH2 = PT-PH2O
= 715-23.8 = 691.2torr
P = 691.2/760 = 0.91 atm
V = 11.9ml = 0.0119L
T = 25C = 25+273 = 298K
PV = nRT
n = PV/RT
= 0.91*0.0119/0.0821*298 = 0.0004426moles
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