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Dalton's Law of Partial Pressure MCQ - Practice Questions with Answers

Edited By admin | Updated on Sep 25, 2023 25:23 PM | #NEET

Quick Facts

  • Dalton’s Law of Partial Pressure is considered one the most difficult concept.

  • 38 Questions around this concept.

Solve by difficulty

A mixture of gases contains H2 and O2 gases in the ratio of 1 : 4 (w/w). What is the molar ratio of the two gases in the mixture ?

A gaseous mixture was prepared by taking equal mole of CO2 and N2. If the total pressure of the mixture was found 1 atmosphere, the partial pressure of the nitrogen (N2) in the mixture is:

Equal masses of H2,O2 and methane have been taken in a container of volume V at temperature 27oC in identical conditions. The ratio of the volumes of gases H2:O2: methane would be :

A mixture of N2 and Ar gases in a cylinder contains 7 g of N2 and 8 g of Ar. If the total pressure of the mixture of the gases in the cylinder is 27 bar, the partial pressure of N2 is : [Use atomic masses (in gmol 1 ) N=14,Ar=40 ]

 

A gas mixture contain 35% He and 65%CH4 by volume at a gives temperature and pressure.The Percentage by mass of methane in the mixture?

A Mixture of N2 and Ar gas in a cyclinder contains 5 g N2 and 8 g at Ar . If the total pressure of the mixture of gases in the cyctinder is 30 bar, the partial Pressure at N2 is [use atomic mass N=14Ar=40 ]

A 15 g Mixture of Hydrogen and helium is contained in a vessel at capacity.0.225dm3 at 5 bar and 27C..
The Mass of Helium in the Mixture is ---g

200Ml of  O2( g) effuse from a Porous container in 200 sec .75 Ml of unknowns gas effuse under the same condition of temperature and pressure in 225sec. Calculates vapour density of unknown gas?

A Mixture of Hydrogen and oxygen contain 40 % Hydrogen by Mass when the pressure is 2.2 bar. The Partial Pressure of Hydrogen in bar?

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The Pressure of a Moist was at 27C is 8 atm. The volume of the container is doubled at the same temperature. [PH2 at 27C=.2 atm]The New  pressure of the Moist gas is ..×101 atm

Concepts Covered - 0

Dalton’s Law of Partial Pressure

According to Dalton's law, "Total pressure of a mixture of non-reacting gases is equal to the sum of partial pressure of these gases at constant temperature and constant volume."

\\\mathrm{P_{\operatorname{mix}}=P_{1}+P_{2}+P_{3}}\\\\\mathrm{Here \: P_{mix }= pressure\: of\: the\: gaseous\: mixture}\\\\\mathrm{P_{1}, P_{2}, P_{3}= partial \: pressure \: of \: gases}\\\\\mathrm{Partial\: pressure \: of \: any\: gas\: =\: \frac{\%\: of\: that\: gas\: }{100} \times P_{mix}}\\\\\mathrm{\%\: of\: a\: gas\: in\: a\: mixture\: =\: \frac{Partial \: pressure\: of\: the\: gas}{Total \: pressure\: of\: gaseous \: mixture} \times 100}

\\\mathrm{Partial\: pressure \: of \: any \: component\: A \: is\: given\: as}\\\\\mathrm{P_{A}=\frac{moles \: of\: A}{Total \: moles} \times P_{Total }}\\\\\mathrm{Total\: pressure\: of\: a\: mixture\: having\: different\: components \: is\: given \: as}\\\\\mathrm{P_{mix}\: =\: \left(n_{1}+n_{2}+n_{3} \ldots . .\right) \frac{R T}{V}}\\\\\mathrm{P_{mix}\: =\: \left(\frac{w_{1}}{m_{1}}+\frac{w_{2}}{m_{2}}+\frac{w_{3}}{m_{3}}\right) \ldots . \frac{R T}{V}}\\\\\mathrm{Here\: w_{1}, \: w_{2},\: w_{3}\: =\: weight \: of\: components\: or\: non-reacting \: gases}\\\mathrm{ and \: m_{1},\: m_{2},\: m_{3}\: are \: their\: molar\: masses.}

\\\mathrm{T\: =\: Temperature \: in \: Kelvin.}\\\mathrm{V\: =\: Volume in litre.}

  • When a gas is collected over water it mixes with water vapours so the correct pressure of moist gas is given as
    P(moist gas) = P(dry gas) + P(VP of water)
    P(dry gas) = P(moist gas) - P(V.P of water)
    Aqueous tension = Partial pressure of water vapour in moist gas.
  • Vapour pressure of water varies with temperature. For example, Aa 0oC, it is 4.6 torr while at 25oC it is 23.8 torr.

NOTE: Dalton's law is not applicable for a mixture of reacting gases like Nand O2, SO2 and O2.

Partial pressure in terms of mole fraction
According to ideal gas equation, if n1 is the number of molecules of one constituent gas of the gaseous mixture then P1 is the pressure exerted by the gas at temperature(T) enclosed in the volume (V).

\mathrm{P_{1}=\frac{n_{1} R T}{V}}\quad \quad \quad ..........(i)
Similarly for the other two constituting gases of the gaseous mixture

\\\mathrm{P_{2}\: =\: \frac{n_{2}RT}{V}}\\\\\mathrm{P_{3}\: =\: \frac{n_{3}RT}{V}}

According to Dalton's Law of partial pressures

\\\mathrm{P_{Total}\: =\: P_{1}\: +\: P_{2}\: +\: P_{3}\: +\ldots}\\\\\mathrm{=\: \frac{n_{1} R T}{V}\: +\: \frac{n_{2} R T}{V}\: +\: \frac{n_{3} R T}{V}\: +\: \ldots}\\\\\mathrm{P_{total}\: =\:(n_{1}\: +\: n_{2}\: +\: n_{3}) \frac{RT}{V}}\quad \quad \quad ........(ii)

That means the total partial pressure of the mixture is determined by the total number of moles present.
Dividing equation (i) by (ii) we get.

\\\mathrm{\frac{P_{1}}{P_{total}}\: =\: \left(\frac{n_{1}}{n_{1}+n_{2}+n_{3}}\right) \frac{R T V}{R T V}}\\\\\mathrm{=\: \frac{n_{1}}{n_{1}+n_{2}+n_{3}}\: =\: \frac{n_{1}}{n}}\\\\\mathrm{where n=n_{1}+n_{2}+n_{3}}

\mathrm{Now,\: \frac{n_{1}(moles \: of\: 1^{st}\: gas)}{n(Total\: number\: of\: moles)}= Mole\: fraction\: of\: first\: gas \: x_{1}}

Mole fraction:
It is the ratio of the number of moles of an individual gas to the total number of moles of all gases present in the container.

\\\mathrm{\frac{P_{1}}{P_{total}}\: =\: x_{1}}\\\\\mathrm{Thus,\: P_{1}\: =\: x_{1} P_{total}}\\\\\mathrm{Similarly P_{2}\: =\: x_{2}P_{total}}\\\\\mathrm{Therefore\: the \: generalised \: equation \: becomes}\\\\\mathrm{P_{i}\: =\: x_{i}P_{Total}}

Where, Pi = partial pressure of the ith gas
           xi = mole fraction of the ith gas
Thus, the partial pressure of a gas in the mixture of gases is the product of its mole fraction and the total pressure of the mixture.

Applications

  • Jet aeroplane flying at high altitude need pressurization of cabins so as to make partial pressure of oxygen sufficient for breathing, as the air pressure decreases with increase in altitude.
  • Calculation of the pressure of dry gas collected over water: When the gas is collected over water it is moist because of the water vapours. Saturated water vapour exerts its own partial pressure called aqueous tension. So, in order to calculate the partial pressure of dry gas, aqueous tension is subtracted from the pressure of moist gas (Pmoist gas or PTotal)
    Pdry gas = Ptotal  - Aqueous tension

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