Question

A sealed-tube manometer can be used to measure pressures below atmospheric pressure. The tube above the mercury is evacuated. When there is a vacuum in the flask, the mercury levels in both arms of the U-tube are equal. If a gaseous sample is introduced into the flask, the mercury levels are different. The difference 'h' is a measure of the pressure of the gas inside the flask. If 'h' is equal to 6.5cm, calculate the pressure in the flask in torr, pascals, and atmospheres. (I need help trying to figure out HOW to get the answer, not what the answer is.)

Answer 1

This problem employs conversion of units.

1cm Hg=10 mmHg
1mmHg= 1 Torr
1 atm = 760mmHg
1 atm = 101,325 Pa

6.5cmHg*(10mmHg/1cmHg)= 65 mmHg = 65 Torr
65mmHg*(1 atm/760mmHg)= 0.086 atm
0.086atm*(101,325 Pa/1 atm)= 8665.95 Pa

Answer 2

The correct answers are:

6.5 cm = 65.00001052 torr
6.5 cm = 8665.93 Pa
6.5 cm = 0.08552632119 atm

Explanation

The conversion rate from centimeters mercury (cm Hg) to torr is
1 torr = 0.099999983814461 cm.

We have 6.5 cm; this means to convert we divide:
6.5/0.099999983814461 = 65.00001052

The conversion rate from cm Hg to Pascals (Pa) is
1 cm = 1333.22 Pa

We have 6.5 cm; this means to convert we multiply:
6.5(1333.22) = 8665.93

The conversion rate from cm Hg to atmospheres (atm) is
1 atm = 75.999995199606 cm

We have 6.5 cm; this means to convert we divide:
6.5/75.999995199606 = 0.08552632119