The vapor pressure of water changes with temperature, as shown here. A student d
ID: 927383 • 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 3.00 min , 11.8 mL of water-saturated H2(g) is collected. The temperature and pressure of the system are 25 C and 715 torr.
How many moles of hydrogen gas are produced?
Express your answer to three significant figures and include the appropriate units
T (C) P (torr) 21 18.7 22 19.8 23 21.1 24 22.4 25 23.8 26 25.2 27 26.7 28 28.4 29 30.0 30 31.8Explanation / Answer
H2O ---> H2 + 1/2O2
H2 volume = 11.8 ml = 0.0118 L T = 25C = 25+ 273= 298 K
P totla = 715 torr = PH2O + PH2 = 23.8+ PH2
PH2 = 715-23.8 = 691.2 torr = 691.2 /760 atm = 0.9095 atm
we use PV = nRT equation
0.9095 x 0.0118 = n x 0.08206 x 298
n = moles of H2 = 4.39 x 10^ -4
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