A sample of gas has a mass of 0.555 G . Its volume is 119 mL at a temperature of 85C and a pressure of 739 mmHg.
Find the molar mass of the gas.
Find the molar mass of the gas.
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Hey Eli again :)!
This question requires you to use the ideal gas equation PV=nRT where P represents pressure, V represents volume in liters, n represents moles, R represents the gas constant typically 0.08206 L atm/ mol k (if the pressure is in atmospheres), and T represents the temperature in kelvin (K=C+273). The key is to use this equation to find n (the moles of gas) and then divide it by the given mass (0.555g) to find the molar mass.
So before we plug in our given information, let's convert all of our units to the correct form. Like mentioned above, the gas constant requires the pressure to be in atms and so we must convert 739 mmHg to atms. 1 atm = 760 mmHg so divide 739 by 760 and you should get about 0.97 atms. Now the volume must be in liters so 119mL divided by 1000 will give us the new volume in liters, which should be 0.119L. Finally, our temperature must be in kelvins and so we just add the celsius temperature by 273 to convert it to kelvins (85 + 273 = 358K). Now we can plug everything into the equation:
(0.97 atm)(0.119L) = n(0.08206 L atm/mol K)(358K). Now we just use algebra to solve for n, which is the moles of the gas. You should get about 3.9x10^-3 moles of the gas. Now the final step is to divide the mass 0.555g by our newfound moles: (0.555g)/(3.9x10^-3 moles) = 141.25 or about 140 g/mol of the gas and that is your molar mass.
I hope this helped and feel free to ask more questions if this was confusing! :)
This question requires you to use the ideal gas equation PV=nRT where P represents pressure, V represents volume in liters, n represents moles, R represents the gas constant typically 0.08206 L atm/ mol k (if the pressure is in atmospheres), and T represents the temperature in kelvin (K=C+273). The key is to use this equation to find n (the moles of gas) and then divide it by the given mass (0.555g) to find the molar mass.
So before we plug in our given information, let's convert all of our units to the correct form. Like mentioned above, the gas constant requires the pressure to be in atms and so we must convert 739 mmHg to atms. 1 atm = 760 mmHg so divide 739 by 760 and you should get about 0.97 atms. Now the volume must be in liters so 119mL divided by 1000 will give us the new volume in liters, which should be 0.119L. Finally, our temperature must be in kelvins and so we just add the celsius temperature by 273 to convert it to kelvins (85 + 273 = 358K). Now we can plug everything into the equation:
(0.97 atm)(0.119L) = n(0.08206 L atm/mol K)(358K). Now we just use algebra to solve for n, which is the moles of the gas. You should get about 3.9x10^-3 moles of the gas. Now the final step is to divide the mass 0.555g by our newfound moles: (0.555g)/(3.9x10^-3 moles) = 141.25 or about 140 g/mol of the gas and that is your molar mass.
I hope this helped and feel free to ask more questions if this was confusing! :)
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PV = nRT
Just be sure you are consistent with units; for instance, temperature must be in Kelvin.
You are are solving for n, the number of moles. And you are given the mass.
Just be sure you are consistent with units; for instance, temperature must be in Kelvin.
You are are solving for n, the number of moles. And you are given the mass.