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Chemistry Forums for Students => Physical Chemistry Forum => Topic started by: Win,odd Dhamnekar on November 19, 2020, 08:46:19 AM

How to answer this question?

You have all the information you need to calculate the molar mass from the ideal gas law.

Hello,
Weight of the unknown liquid inside the bulb after completion of reaction is 50.1879 grams  50.0230 grams =0.1649 grams.
Volume of the water= 102.7535 grams  50.0230 grams = 52.7305 grams = volume of the vapour of liquid after its immersion in oil bath at 423.15 K( 150° C) and 0.980 bar.
Using ideal gas law equation PV=nRT, [itex]\frac{0.980 bar*0.0527305 liters}{0.0831447 bar*liters/(mol*K)*423.15 K}=0.001468787 mol [/itex]
Molar weight of the unknown liquid =0.1649 grams/0.001468787 mol= 112.269 grams/mol. Its molecular weight is 1.86427e22 u.

The approximate molecular weight  112.

Definitions of molecular mass, molecular weight, molar mass and molar weight
Molecular mass (molecular weight) is the mass of one molecule of a substance and is expressed in the unified atomic mass units (u). (1 u is equal to 1/12 the mass of one atom of carbon12)
Molar mass (molar weight) is the mass of one mole of a substance and is expressed in g/mol

Molar weight of the unknown liquid =0.1649 grams/0.001468787 mol= 112.269 grams/mol. Its molecular weight is 1.86427e22 u.
No. You have divided the molar mass by N_{A}, which gives you the molecular weight in g. What is the molecular weight in u?

Oh! You are correct. AWK's answer is correct. Thanks for pointing out my mistake. The molecular weight in u 1s 112.168

Remember: The molecular weight in u is numerically equal to the molar mass in g/mol. (This follows from the definitions.)