What is the pressure of the gas trapped in the apparatus shown below when the atmospheric pressure is 720 mmHg ?
A) 12 mmHg
B) 708 mmHg
C) 720 mmHg
D) 732 mmHg
E) 760 mmHg

Question

What is the pressure of the gas trapped in the apparatus shown below when the atmospheric pressure is 720 mmHg ? 
A) 12 mmHg 
B) 708 mmHg 
C) 720 mmHg 
D) 732 mmHg 
E) 760 mmHg

Quizplus · Accepted Answer

The pressure of the gas is equal to the difference between the atmospheric pressure and the pressure exerted by the water column. The height of the water column is 708 mmHg (760 - 52) as the water exerts a pressure of 1 atm (760 mmHg) at the bottom of the tube. Therefore, the pressure of the gas is 720 - 708 = 12 mmHg. Choice A is incorrect as it is the pressure exerted by the water column alone. Choice C is incorrect as it is the same as atmospheric pressure. Choice D is incorrect as it is the sum of atmospheric and water column pressures. Choice E is incorrect as it is the atmospheric pressure alone.

What Is the Pressure of the Gas Trapped in the Apparatus