Question

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

The values above go in this order 21 is T(C) and 18.7 is (Ptorr) goes in this order all the way down

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 4.00 min , 12.8 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?

Answer 1

moles of H₂ produced = 4.76 x 10^-4moles

Explanation

Total pressure = 715 torr

vapor pressure of water at 25^oC = 23.8 torr

presure of H₂ = Total pressure - vapor pressure of water at 25^oC

presure of H₂ = 715 torr - 23.8 torr

presure of H₂ = 691.2 torr

presure of H₂ = 691.2 torr * (1 atm / 760 torr)

presure of H₂ = 0.90947 atm

volume of H₂ = 12.8 mL = 0.0128 L

Temperature of H₂ = 25 ^oC = 298 K

According to ideal gas law

moles of gas = [(pressure of gas) * (volume of gas)] / [(temperature of gas) * (R)]

Where R = gas constant = 0.0821 L-atm/mol-K

moles of H₂ = [(0.90947 atm) * (0.0128 L)] / [(298 K) * (0.0821 L-atm/mol-K)]

moles of H₂ = 4.76 x 10^-4 moles