DO NOW:

1. Convert 770 mm Hg atm

2. Convert 100,900 Pa atm mm Hg

Measuring

with Barometers and Manometers

What is atmospheric pressure?The pressure exerted by theair in the atmosphere is calledatmospheric pressure. It isa result of the fact that air hasmass and is attracted byEarth’s gravity. This attractionproduces a force. The forceexerted on a unit area of theEarth’s surface is atmosphericpressure.

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.

BAROMETERSYou can measure the pressure of the atmosphere with abarometer.

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

A.

Measuring the Pressure of Confined Gases

B.

Measuring the Pressure of Confined Gases

C.

Manometer Practice Problems

A gas container is fitted withan open-end manometer. The level of the manometeris 15mm lower on the openside. Using a laboratorybarometer, you find that theatmospheric pressure is750mmHg. What is thepressure in atmospheres, ofthe gas in the container?

A soccer ball is attached toan open-end manometer. The mercury level in themanometer is 10mmlower on the side attachedto the ball than on theside open to theatmosphere. Atmosphericpressure has already beendetermined to 770 mmHg. What is the gas pressurein the ball in mmHg?

Suppose you are measuring the pressure inside a sealed cabinet using an open-ended manometer. The atmospheric pressure is 662.4 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 isfilled with mercury.

Themercury level is 12 mmhigher on the side

open tothe atmosphere. What

isthe total pressure of

the gas, in kPa, if theatmospheric pressure

is752.4 mm Hg?

An open manometer isfilled with mercury andconnected to a containerof hydrogen gas. Themercury level is 57 mmhigher in the arm of the tube connected to thehydrogen. If theatmospheric pressure is 748.6 mm Hg, what is thepressure of the hydrogengas, in atmospheres?

An open manometerconnected to a tank ofargon has a mercury level83 mm higher in theatmospheric arm. If theatmospheric pressure is576.8 mm Hg, what is thepressure of the argon inkPa?