Question

What is the pressure in a gas container that is connected to an open-end u-tube manometer if the pressure of the atmosphere is 742 torr and the level of mercury in the arm connected to the container is 8.60 cm higher than the level of mercury open to the atmosphere?

Answer 1

Answer: 656 mmHg

Step-by-step explanation:

Manometers are used to measure the pressure in a container by comparing it to normal atmospheric pressure.

First convert the atmospheric pressure to mmHg

1 torr = 1 mmHg

Therefore, the atmospheric pressure = 742 mmHg

Since the arm connected is higher than the level of the Mercury open to the atmosphere, then the gas pressure is lower than the atmospheric pressure.

Hence,

Pgas = Patm - change in height

Pgas = 742 mmHg - 8.6 cmHg

Balance the unit: 10 mm = 1 cm

Then,

Pgas = 742 mmHg - 86 mmHg

Pgas = 656 mmHg

The gas pressure in the container is 656 mmHg.

Answer 2

First, know that 8.60 cm = 86.0 mm, which is equivalent to an 86.0 torr pressure difference between the atmosphere and the container.

In this situation the pressure in the container is less than the atmosphere.

742 - 86 = 656 torr