The vapor pressure of water changes with temperature, as shown here. A student d

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 , 14.5 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?

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 31.8

Explanation / Answer

PV = nRT

P = P of H2 - P of Water

P = 715 torr - 23.8 torr

P = 691.2 torr

P = 691.2 / 760 = 0.9095 atm

V = 14.5 /1000 = 0.0145 L

n = PV /RT

n = ((0.9095)*(0.0145)) / (0.0821*298)

n = 5.39 * 10^-4 moles

n = 0.539 milli moles

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