Question

A given mass of gass at -70 cm exerted a pressure 50 cm of hg what pressure will it exert 27°c

Answer 1

ans. is co2
The idea here is that you need to figure out the molar mass of the gas by using its density under the given conditions for pressure and temperature.

Your tool of choice will be the ideal gas lawequation

PV=nRT−−−−−−−−−−

Here

P is the pressure of the gas

V is the volume it occupies

n is the number of moles of gas present in the sample

R is the universal gas constant, equal to 0.0821atm Lmol K

T is the absolute temperature of the gas

Start by converting the pressure of the gas to atmospheres and the temperature to Kelvin. You will have

76cmHg⋅1.0 atm76cmHg=1.0 atm

and

T[K]=27∘C+273.15=300.15 K

Now, you know that the density of the gas, ρ, can be expressed by using the mass of the sample, let's say m, and the volume it occupies, V

ρ=mV

The number of moles of gas can be expressed by using the mass of the sample and the molar mass of the gas, let's say MM

n=mMM

Plug this into the ideal gas law equation to get

PV=mMM⋅RT

Rearrange to isolate the molar mass of the gas

MM=mV⋅RTP

This is equivalent to

MM=ρ⋅RTP

Plug in your values to find

MM=1.80 gL−1⋅0.0821atm⋅Lmol⋅K⋅300.15K1.0atm

MM=44 g mol−1→ rounded to two sig figs

The closest match is carbon dioxide, which has a molar mass of

MM CO2=44.01 g mol−1