Question

Question #5cddc

Answer 1

The answer is `693.5 mmHg`.

The total pressure reqistered for the collected gas represents the sum of the partial pressures of water(its vapor pressure ) and hydrogen gas. We know that

`P_(TOTAL) = P_(H_2) + P_(water)`

Usually, water's vapor pressure at various temperatures is given, but you could try and calculate it using the given temperature by

`P = exp(20.386 - 5132/T) mmHg`, where temperature is in K and pressure in mmHg. Using this approximation formula (wikipedia link: http://en.wikipedia.org/wiki/Vapour_pressure_of_water) we get

`P_(water) = exp(20.386 - 5132/(273.15+30)) = 31.7 mmHg`

I've looked up the actual value of the vapor pressure at that temperature and it's listed at

`P_(water) = 31.5 mmHg`, which is pretty close to the value determined using the approximation formula.

Let's use the `31.5 mmHg` vapor pressure. This will result in

`P_(H_2) = P_(TOTAL) - P_(water) = 725 - 31.5 = 693.5 mmHg`

Water's vapor pressure values:

http://intro.chem.okstate.edu/1515sp01/database/vpwater.html