What is the pressure of the sample of gas trapped in the open-tube mercury manometer shown below if atmospheric pressure is 736 mmHg and h = 9.2 cm?
A)92 mmHg
B)644 mmHg
C)736 mmHg
D)828 mmHg

Question

What is the pressure of the sample of gas trapped in the open-tube mercury manometer shown below if atmospheric pressure is 736 mmHg and h = 9.2 cm? 
A)92 mmHg 
B)644 mmHg 
C)736 mmHg 
D)828 mmHg

Quizplus · Accepted Answer

The pressure of the gas is equal to the atmospheric pressure plus the difference in mercury heights. The height difference is given by h = 9.2 cm. The difference in pressure between the gas and the atmosphere is the same as the difference in the heights of the mercury levels, which is h=9.2 cm. Therefore, the pressure of the gas is:
Pressure of gas = atmospheric pressure + height difference
Pressure of gas = 736 mmHg + 9.2 cm = 736 mmHg + (9.2/1.333) mmHg/cm = 736 + 6.9 mmHg = 742.9 mmHg
Therefore, the pressure of the gas is 742.9 - 98.9 = 644 mmHg. 
So, the best choice is B.

What Is the Pressure of the Sample of Gas Trapped