A student sets up the experiment described in procedure A. A current of 0.890 A

Question

A student sets up the experiment described in procedure A. A current of 0.890 A is passed through a cell for 6 minutes and 45 c. During that same time period, the student collects 46.00 mL of hydrogen gas over water at a temperature of 22 degrees Celsius. The atmospheric pressure is 30.85 in Hg.

b) What is the vapor pressure of water at 22 degrees Celsisus

c) What is the pressure of dry H2 gas in mmHg? In atm

d) Assuming ideal gas behavior, how many moles of H2 gas were collected?

e) How many moles were transferred?

Explanation / Answer

b)

from database data... 19.8 torr is the Vapor pressure of water at 22°C

note that 19.8torr = 19.8 mm Hg

c)

Pgas = from ideal gas law

Ptotal = PH2 + Pvapor

Ptotal = 30.85 in Hg = 783.59001 mm Hg

PH2 = Ptotal - PVapor = 783.59001-19.8 = 763.79001 mm Hg

in atm --> 763.79001/760 = 1.00498atm of H2

d)

PV = nRT

n = PV/(RT) = 1.00498*0.046/(0.082*295) = 0.001911 mol of H2

e)

mol of e- transferred

2H+ + 2e- --> H2(g)

so

0.001911*2 = 0.003822 mol of E-

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