# DO NOW: Convert 770 mm Hg  atm Convert 100,900 Pa  atm  mm Hg.

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DO NOW: Convert 770 mm Hg  atm Convert 100,900 Pa  atm  mm Hg

Measuring with Barometers and Manometers

What is atmospheric pressure?
The pressure exerted by the air in the atmosphere is called atmospheric pressure. It is a result of the fact that air has mass and is attracted by Earth’s gravity. This attraction produces a force. The force exerted on a unit area of the Earth’s surface is atmospheric pressure.

We are used to living at 1 Atm of pressure, so we rarely even take notice of it. We normally don't feel the pressure on us because the human body is primarily made up of liquid, and liquids are basically non- compressible. At times, however, we do notice changes of pressure, primarily in our ears. You may have noticed your ears "popping“ when flying, driving in the mountains, or even going up and down in elevators. This is because our ears have an air space in them, and air, like all other gases, is compressible.

BAROMETERS You can measure the pressure of the atmosphere with a
A mercury barometer is a glass tube that is filled with mercury, and then inverted into a reservoir of mercury. The mercury in the tube immediately seeks a height so that the pressure exerted on the surface of the mercury in the reservoir is exactly balanced by the pressure exerted by the mercury column. The height of the mercury column that will be balanced by a pressure of exactly 1 atmosphere is 760 millimeters (mm) at sea level.

Mercury Barometer

MANOMETERS You can measure the pressure in a closed container. A simple manometer can be made using a U-shaped glass tube filled with mercury. One end of the tube opens into the container in which the gas pressure is to be measured. The other end of the tube is open to the surrounding atmosphere. To determine the pressure in the container, calculate the difference between atmospheric pressure and the pressure in the container (the difference between the heights of the two mercury columns).

U-Tube Manometer

Measuring the Pressure of Confined Gases

Measuring the Pressure of Confined Gases
B.

Measuring the Pressure of Confined Gases

Manometer Practice Problems
A gas container is fitted with an open-end manometer. The level of the manometer is 15mm lower on the open side. Using a laboratory barometer, you find that the atmospheric pressure is 750mmHg. What is the pressure in atmospheres, of the gas in the container?

A soccer ball is attached to an open-end manometer
A soccer ball is attached to an open-end manometer. The mercury level in the manometer is 10mm lower on the side attached to the ball than on the side open to the atmosphere. Atmospheric pressure has already been determined to 770 mmHg. What is the gas pressure in the ball in mmHg?

Suppose you are measuring the pressure inside a sealed cabinet using an open- ended manometer. The atmospheric pressure is mmHg. If the mercury level on the side open to the atmosphere is 3.6mm higher than the side attached to the cabinet, what is the pressure inside the cabinet in units of kPa?

An open manometer is filled with mercury. The mercury level is 12 mm higher on the side open to the atmosphere. What is the total pressure of the gas, in kPa, if the atmospheric pressure is 752.4 mm Hg?

An open manometer is filled with mercury and connected to a container of hydrogen gas. The mercury level is 57 mm higher in the arm of the tube connected to the hydrogen. If the atmospheric pressure is mm Hg, what is the pressure of the hydrogen gas, in atmospheres?

An open manometer connected to a tank of argon has a mercury level 83 mm higher in the atmospheric arm. If the atmospheric pressure is mm Hg, what is the pressure of the argon in kPa?

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