Question

A mixture of krypton and neon gases, in a 8.26 L flask at 42 °C, contains 11.8 grams of krypton and 7.10 grams of neon. The partial pressure of neon in the flask is atm and the total pressure in the flask is atm?

A mixture of krypton and neon gases, in a 8.26 L flask at 42 °C, contains 11.8 grams of krypton and 7.10 grams of neon. The partial pressure of neon in the flask is
atm and the total pressure in the flask is
atm

Answer 1

The total pressure is `"1.54 atm"` and the partial pressure of neon is `"1.10 atm"`.

Explanation:

We can use Dalton's law to answer this question:

`P_x=P_t(n_x/n_t)`,

where:

`P_x` is the partial pressure of a gas in a mixture, `P_t` is the total pressure of all the gases in the mixture, `n_x` is the number of moles of a gas in a mixture, and `n_t` is the total number of moles in the mixture, and `(n_x/n_t)` is the mole fraction of a gas in the mixture.

Before we do that, we must determine the moles of each gas, and add them to get total moles `(n_t)`. Then we'll use the ideal gas law to determine the total pressure `(P_t)`.

Moles Kr and Ne in flask

Divide the mass of each gas by its molar mass (atomic weight on periodic table in g/mol).

`n_"Kr"=(11.8"g Kr")/(83.798"g"/"mol")="0.141 mol"`

`n_"Ne"=(7.10"g Ne")/(20.180"g"/"mol")="0.352 mol"`

Total moles

`n_t="0.141 mol + 0.352 mol"="0.493 mol"`

Total pressure

Ideal gas law

`PV=nRT`,

where:

`P` is pressure, `V` is volume, `n` is total moles, `R` is the gas constant, and `T` is temperature in Kelvins.

Known

`V="8.25 L"`

`n_t="0.493"`

`R="0.082057 L atm K"^(-1) "mol"^(-1)"`

`T="42"^@"C+273.15"="315 K"` `larr` Temp must be in Kelvins

Unknown

`P_t`

Plug the known values into the equation and solve.

`P_t=(0.493color(red)cancel(color(black)("mol"))xx0.082057color(red)cancel(color(black)("L")) "atm" color(red)cancel(color(black)("K"))^(-1) "mol"^(-1)xx315color(red)cancel(color(black)("K")))/(8.26color(red)cancel(color(black)("L")))="1.54 atm"`

Now that we have the total pressure, we can determine the partial pressure of neon `(P_"Ne")` using Dalton's law.

`P_"Ne"=P_t(n_"Ne"/n_t)`

Plug in the known values and solve.

`P_"Ne"="1.54 atm"((0.352color(red)cancel(color(black)("mol")))/(0.493color(red)cancel(color(black)("mol"))))="1.10 atm"` (rounded to three significant figures)

The total pressure is `"1.54 atm"` and the partial pressure of neon is `"1.10 atm"`.