A flask containing helium gas is connected to an open-ended mercury manometer. The open end is exposed to the atmosphere, where the prevailing pressure is 752 torr. The mercury level in the open arm is 26 mm above that in the arm connected to the flask of helium. What is the helium pressure, in torr?
A)−26 torr
B)26 torr
C)726 torr
D)778 torr
E)None of these choices are correct.

Question

Quizplus · Accepted Answer

The pressure of the helium in the flask can be found by adding the difference in mercury levels to the atmospheric pressure. This is because the pressure of the atmosphere (752 torr) is pushing down on the open arm of the manometer, causing the mercury to rise in the other arm until the pressure of the helium in the flask balances out the pressure of the atmosphere. Therefore, the pressure of the helium is 752 + 26 = 778 torr. The correct answer is D.

A Flask Containing Helium Gas Is Connected to an Open-Ended