Question

A 250 mL flask initially contains argon at a pressure of 2.0 atm. Neon is added to the flask until the total pressure reaches 5.0 atm. What is the mole fraction of neon in the final mixture

Answer 1

Answer: The mole fraction of neon in the final mixture is 0.6

Explanation:

According to Dalton's law, the total pressure is the sum of individual pressures.

$p_{total}=p_A+p_B$

Given : $p_{total}$ =total pressure of gases = 5.0 atm

$p_{Ar}$ = partial pressure of argon = 2.0 atm

$p_{Ne}$ = partial pressure of Neon = ? atm    

$5.0atm=2.0atm+p_{Ne}$  

$p_{Ne}=3.0atm$

According to Raoults law, the partial pressure of a gas is equal to its mole fraction mulitiplied by the total pressure.

$p_{Ne}=\chi_{Ne}\times p_{total}$

$\chi_{Ne}$ = mole fraction of Neon

$3.0=\chi_{Ne}\times 5.0$

$\chi_{Ne}=0.6$

Thus mole fraction of neon in the final mixture is 0.6