Question

A gas occupies 100.0 mL at a pressure of 780 mm Hg. What is the volume of the gas when its pressure is increased to 880 mm Hg?

Answer 1

This question has been set by someone who has never used a mercury manometer............we gets `V_2=87.6*mL`

Explanation:

One atmosphere of pressure will support a column of mercury that is `760*mm` high. A manometer is thus a highly visual measure of the strength of a vacuum, or as a measure of atmospheric pressure.

If you put the column under a pressure greater than `1*atm` you are likely to get mercury all over the laboratory, where it will inhabit every crack and every cranny. This is a MAJOR cleanup job, which contract cleaners would not touch.

And so `P_1="780 mm Hg"/("760 mm Hg"*atm^-1)=1.026*atm.`

And so `P_2="880 mm Hg"/("760 mm Hg"*atm^-1)=1.158*atm.`

And now we use old `"Boyle's Law"`, `P_1V_1=P_2V_2.....`, and solve for

`V_2=(P_1V_1)/P_2=(1.026*atmxx100.0*mL)/(1.158*atm)`

`=87.6*mL`

The volume is slightly decreased, as we would expect, why?