Human lungs have evolved to breathe oxygen at a pressure as that in the atmosphere, 0.21 atm. If a particular heliox mixture to be carried by a scuba diver is at a pressure of 7.00 atm, what should be the partial pressure due to helium in order to maintain the pressure due to oxygen at 0.21 atm?

6.79 atm

Explanation:

Applying Dalton's law of partial pressure:

, where = total partial pressure of all the component gases in the mixture, = partial pressure of helium gas, and = partial pressure of oxygen gas.

From the illustration, = 7.00 atm and = 0.21 atm. Hence, the partial pressure due to helium is calculated such that:

=

           = 7.00 - 0.21

              = 6.79 atm

Therefore, the partial pressure due to helium in order to maintain the pressure due to oxygen at 0.21 atm would be 6.79 atm.

a mercury barometer is a device that uses the physical properties of mercury in a tube to measure barometric pressure. mercury barometers are used for : -

1. measurement of atmospheric pressure  

2. determining the altitude of a place

3. weather forecasting

4. calibration and checking of aneroid barometers

5. application in fluid mechanics

6. measurement of pressure in aircrafts

7. surface weather analysis

8. preparation of barographs

9. usage in physical sciences like physics, astronomy & chemistry

10. preparation of aircraft altimeters

characteristics of mercury barometer : -

1.used to define and measure atmospheric pressure.

2.on the average at sea level the column of mercury rises to a height of about 760 mm.

3.this quantity is equal to 1 atmosphere.

4.it is also known as standard atmospheric pressure.

5.a barometer in which the weight of a column of mercury in a glass tube with a sealed top is balanced against that of the atmosphere pressing on an exposed cistern of mercury at the base of the mercury column, the height of the column varying with atmospheric pressure.