Question

A 200mL flask contains oxygen at $200\,trim\,Hg$ and a $300mL$ flask contains neon at $100mmHg$. The two flasks are connected so that each gas fills their combined volumes. What is the partial pressure of neon in the final mixture?
(Assuming no change in temperature)
A. $60mmHg$
B. $80mmHg$
C. $100mmHg$
D. $150mmHg$
E. $200mmHg$

Answer 1

Write down all the given value’s and also make a note of what is supposed to be determined. Make a note of all gas laws and cross out the laws which do not consider temperature as constant. In the End, You will have a law which directly relates pressure and volume of a gas while keeping the temperature constant.

Complete step by step answer:
First, Let us mention all the given data for the question.
Initial Volume of Oxygen $= 200mL$
Initial Pressure of Oxygen$= 200\,trim\,Hg$
Initial Volume of Neon $= 300mL$
Initial Pressure of Neon $= 100\,mm\,Hg$
We need to determine the Partial pressure of Neon
The Formula we will be using will be based on Boyle's Law of Gases.
Boyle’s law states that pressure of a gas varies inversely with volume at constant temperature.
The formula is as follows:

${P_{partial}} = {P_{Initial}}\, \times \dfrac{{{V_{N{e_{(INITIAL)}}}}}}{{{V_{TOTAL}}}}$
Now, in the above equation, the unknown value is ${P_{partial}}$for Neon Gas. All the other Value’s can be determined for the information given in the question.

For starters, Let us find out the value of total volume.
Since Volume is a scalar quantity it can be added directly. Which means that the total volume of the mixture will be equal to the sum of volume of individual gases in the mixture.
${V_{total}} = {V_{Neon}} + {V_{Oxygen}}$

From the above mentioned data, we can substitute the value of ${V_{neon}}\,and\,{V_{oxygen}}$.
we get,
${V_{total}} = 200 + 300 \Rightarrow 500\,mL$

Since all the other variables in the formula are known, let us substitute the values.
${P_{partial}} = 100mmHg \times \dfrac{{300mL}}{{500mL}}\,$
from solving the above equation, we get:
${P_{partial}} = 60mmHg$

Hence, Option A is the correct answer.

Note: Please note that in the solution the pressure of oxygen was not used, it was not needed as in the final solution we did not need the value of total pressure of the mixture or the partial pressure of the oxygen. Be careful while examining the data that has been given, since not all of them will be required to solve the numerical.
All the above calculations are done assuming ideal behaviour of the gas.