Question

Question #c8a2e

Answer 1

`"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