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# accurate mass of Ideal gas

• In order to calculate the most accurate mass of an ideal gas using the relationPV= nRT

what conditions of presuusre and temperatur would be used?

Ans. We need mass to put into the final equation.....gases dont have masses they have volumes....so we have to liquefy them by applying high pressure and low temperature. Is this correct?

• Originally posted by hoay:

In order to calculate the most accurate mass of an ideal gas using the relationPV= nRT

what conditions of presuusre and temperatur would be used?

Ans. We need mass to put into the final equation.....gases dont have masses they have volumes....so we have to liquefy them by applying high pressure and low temperature. Is this correct?

Gases do have masses.

You'll need to provide the full exam question to calculate.

• Here is the full MCQ from CIE....

Measured values of the pressure, volume and temperatureof a known mass of a gaseous compound are to be susbstituted into the equation

Pv= nRT

In order to calculate the relative molecular mass of the compound

Which conditions of pressure and temperature would give the most accurate valuesof Mr?

pressure             temperature

A                      high                     high

B                      high                     low

C                      low                     high

D                      low                     low

• The weights of gases are dependent on the gravitational force acting upon them, and difficult to measure directly, but the masses of gases are independent on the gravitational force acting upon them, and can be calculated using PV=nRT if simplified to ideal gas behavior, where P, V and T can be directly measured with appropriate apparatus, and sample mass = number of moles x molar mass. The mass of the gases obtained will be the weighted average of all gases present.
• Originally posted by hoay:

Here is the full MCQ from CIE....

Measured values of the pressure, volume and temperatureof a known mass of a gaseous compound are to be susbstituted into the equation

Pv= nRT

In order to calculate the relative molecular mass of the compound

Which conditions of pressure and temperature would give the most accurate valuesof Mr?

pressure             temperature

A                      high                     high

B                      high                     low

C                      low                     high

D                      low                     low

For this particular MCQ, the answer is C, because the behavior of gases approach ideal gas behavior most closely at high temperatures and low pressures. PV=nRT only holds true for ideal gases, not real gases.
• Okay. thank you.

Can you through some light on the triplet point?

Has this anything to do with the triplet point?

• Originally posted by hoay:

Okay. thank you.

Can you through some light on the triplet point?

Has this anything to do with the triplet point?

No, the "high temperature low pressure" for ideal gas behavior is a separate concept from the triple point of a species.

A gas behaves more like an ideal gas at higher temperature and lower pressure, as the potential energy due to intermolecular forces becomes less significant compared with the particles' kinetic energy, and the size of the molecules becomes less significant compared to the empty space between them.

Wikipedia (Uni level) : https://en.wikipedia.org/wiki/Ideal_gas
A level syllabus relevance : http://www.chemguide.co.uk/physical/kt/realgases.html

The triple point of a substance is the temperature and pressure at which the three phases (gas, liquid, and solid) of that substance coexist in thermodynamic equilibrium.

Wikipedia (Uni level) : https://en.wikipedia.org/wiki/Triple_point
A level syllabus relevance : http://www.chemguide.co.uk/physical/phaseeqia/phasediags.html