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96 gram of gas occupies a volume is 84 gram of nitrogen gas are the similar condition of temperature and pressure find the molecular weight of unknown gas |
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Answer» I would determine the mass of a fixed volume of the gas at a known TEMPERATURE and pressure and then use the IDEAL Gas Law to calculate the molar mass.Explanation:EXAMPLEThe mass of an evacuated 255 mL flask is 143.187 g. The mass of the flask filled with an unknown gas at 25.0 °C and 265 Torr is 143.289 g.SolutionThe Ideal Gas Law is∣∣∣∣¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯aaPV=nRTaa∣∣−−−−−−−−−−−−−−− SINCE n=massmolar mass=mM , we can write the Ideal Gas Law as∣∣∣∣¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯aaPV=mMRTaa∣∣−−−−−−−−−−−−−−−− We can rearrange this to getM=mRTPV m=143.289 g - 143.187 g=0.102 g R=0.082 06 L⋅ATM⋅K-1mol-1 T=(25.0 + 273.15) K=298.75 K P=265torr×1 atm760torr=0.3487 atm V=0.255 L ∴ M=0.102 g×0.082 06L⋅atm⋅K-1mol-1×298.15K0.3487atm×0.255L=28.1 g/molThe molar mass is 28.1 g/mol.∴ The molecular mass is 28.1 u. |
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