Electrolysis and Current The vapor pressure of water changes with temperature, a

Question

Electrolysis and Current 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 2.00 min , 13.2 mL of water - saturated H2 (g) is collected. The temperature and pressure of the system are 25 degree C and 715 torr. Using the stoichometric coefficients in the chemical equation: 2H20(l) - 2H2(g) + 02(g) you can determine that 2.45x10^ - 4 mol of oxygen gas is produced, which is half the number of moles of hydrogen gas produced. Significant Figures Feedback: Your answer 4.90.10^ - 4 moles was either rounded differently or used a different number of significant figures than required for this part. If you need this result for any later calculation in this item, keep all the digits and round as the final step before submitting your answer. Part B Calculate the magnitude of the current in amperes if the number of moles of hydrogen gas produced is 4.91x10^ - 4 mol (from part A). Express your answer to three significant figures and include the appropriate units. Part A How many moles of hydrogen gas are produced? Express your answer to three significant figures and include the appropriate units.

Explanation / Answer

moles of H2 = 4.91 x 10^-4

weight / molecular weight = 4.91 x 10^-4

weight = 4.91 x 10^-4   x 2

weight (w) = 9.82 x 10^-4 g

time (t) = 2min = 2x 60 = 120 sec

equivalent weight of H2 = 1

Faraday = 96500 C

from faraday's law

w = E x i x t / 96500

9.82 x 10^-4 = 1 x i x 120 / 96500

i = 0.790 A

current = i = 0.790 A

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