Transcript (Dalton`s Law)

Chapter 6
Gases
6.8
Partial Pressures (Dalton’s Law)
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Partial Pressure
The partial pressure of a gas
• is the pressure of each gas in a mixture.
• is the pressure that gas would exert if it were by
itself in the container.
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Dalton’s Law of Partial Pressures
Dalton’s law of partial pressures indicates that
• pressure depends on the total number of gas
particles, not on the types of particles.
• the total pressure exerted by gases in a mixture is the
sum of the partial pressures of those gases.
PT = P1 + P2 + P3 +....
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Dalton’s Law of Partial Pressures
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Total Pressure
For example, at STP, 1 mole of a pure gas in a
volume of 22.4 L will exert the same pressure as 1
mole of a gas mixture in 22.4 L.
V = 22.4 L
Gas mixtures
1.0 mole N2
1.0 atm
0.4 mole O2
0.6 mole He
1.0 mole
1.0 atm
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0.5 mole O2
0.3 mole He
0.2 mole Ar
1.0 mole
1.0 atm
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Scuba Diving
• When a scuba diver dives, the increased
pressure causes N2(g) to dissolve in the
blood.
• If a diver rises too fast, the dissolved N2 will
form bubbles in the blood, a dangerous
and painful condition called "the bends."
• Helium, which does not dissolve in the
blood, is mixed with O2 to prepare
breathing mixtures for deep descents.
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Learning Check
A scuba tank contains O2 with a
pressure of 0.450 atm and He at
855 mmHg. What is the total
pressure in mmHg in the tank?
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Solution
1. Convert the pressure in atm to mmHg.
0.450 atm x 760 mmHg = 342 mmHg = PO2
1 atm
2. Calculate the sum of the partial pressures.
Ptotal
= PO2 + PHe
Ptotal
= 342 mmHg + 855 mmHg
= 1197 mmHg
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Learning Check
For a deep dive, a scuba diver uses a mixture of
helium and oxygen with a pressure of 8.00 atm. If
the oxygen has a partial pressure of 1280 mmHg,
what is the partial pressure of the helium?
1) 520 mmHg
2) 2040 mmHg
3) 4800 mmHg
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Solution
3) 4800 mmHg
PTotal = 8.00 atm x 760 mmHg = 6080 mmHg
1 atm
PTotal = PO + PHe
2
PHe = PTotal - PO2
PHe = 6080 mmHg - 1280 mmHg
= 4800 mmHg
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Gases We Breathe
The air we breathe
• is a gas mixture.
• contains mostly N2
and O2, and small
amounts of other
gases.
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Learning Check
A. If the atmospheric pressure today is 745 mmHg,
what is the partial pressure (mmHg) of O2 in the
air?
1) 35.6
2) 156
3) 760
B. At an atmospheric pressure of 714, what is the
partial pressure (mmHg) N2 in the air?
1) 557
2) 9.14
3) 0.109
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Solution
A. If the atmospheric pressure today is 745 mmHg,
what is the partial pressure (mmHg) of O2 in the
air?
2) 156
B. At an atmospheric pressure of 714, what is the
partial pressure (mmHg) N2 in the air?
1) 557
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Blood Gases
• In the lungs, O2
enters the blood,
while CO2 from the
blood is released.
• In the tissues, O2
enters the cells,
which releases CO2
into the blood.
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Blood Gases
In the body,
• O2 flows into the tissues because the partial pressure of
O2 is higher in blood, and lower in the tissues.
• CO2 flows out of the tissues because the partial
pressure of CO2 is higher in the tissues, and lower in the
blood.
Partial Pressures in Blood and Tissue
Gas
O2
CO2
Oxygenated
Blood
100
40
Deoxygenated
Blood
40
46
Tissues
30 or less
50 or greater
15
Gas Exchange During Breathing
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