Question #c8a2e

1 Answer
Nov 22, 2015

Answer:

#"0.9 atm"#

Explanation:

The idea here is that you can use Dalton's law of partial pressures to help you find a relationship between the total pressure of gaseous mixture and the partial pressure of #"B"#.

Now, the mole percent of a gas that's part of a gaseous mixture is simply the mole fraction of that gas multiplied by #100#.

#color(blue)("mole%" = chi xx 100)" "#, where

#chi# - the mole fraction of the gas

This means that you can use the mole percent of gas #"A"# to determine the mole fraction of this gas.

#"mole %" = chi x 100 implies chi = "mole %"/100#

Therefore, you have

#chi_"A" = 10/100 = 0.1#

Since the mixture only contains two gases, #"A"# and #"B"#, it follows that their respective mole fractions must add up to give #1#.

#chi_"A" + chi_"B" = 1#

This means that the mole fraction of #"B"# will be

#chi_"B" = 1 - 0.1 = 0.9#

Now, STP conditions are usually given as a pressure of #"1 atm"# and a temperature of #0^@"C"#.

SIDE NOTE I say usually because the actual conditions for STP are a pressure of #"100 kPa"# and a temperature of #0^@"C"#.

Dalton's law of partial pressures tells you that the partial pressure of each component of a gaseous mixture is proportional to that component's mole fraction.

The total pressure of the mixture can thus be written as

#P_"total" = overbrace(chi_"A" xx P_"total")^(color(red)("partial pressure of A")) + overbrace(chi_"B" xx P_"total")^(color(blue)("partial pressure of B"))#

This means that the partial pressure of #"B"# will be equal to

#P_"B" = chi_"B" xx P_"total"#

#P_"B" = 0.9 * "1 atm" = color(green)("0.9 atm")#

You can read more on mole percent and mole fraction here:

http://socratic.org/questions/what-is-mole-percent