If all the connections in your apparatus are not airtight and some H2 escape( after the initial volume has been recored), will your calculated molar mass be too high or too low why?

Question

If all the connections in your apparatus are not airtight and some H2 escape( after the initial volume has been recored), will your calculated molar mass be too high or too low why?

Answer 1

If the connections are not air tight, then some of the collected gas will be escaping throughout the reaction (experiment). This will lead to and under estimate of the actual volume collected. In calculating the molar mass, one usually uses PV = nRT and solves for n (moles) where n = PV/RT. This shows that n (moles) is directly proportional to V (volume), so when there is a leak, the volume collected is reduced, and the number or moles calculated is smaller than it should be. Since molar mass = mass/moles, the denominator (moles) is smaller than expected, so the calculated molar mass is too high.