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# Dalton's Law of Partial Pressures

## Introduction to calculating pressures of gas mixtures

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### Take Your Time

Credit: Ilse Reijs and Jan-Noud Hutten
Source: http://www.flickr.com/photos/39891373@N07/4177189387
License: CC BY-NC 3.0

Scuba diving is often largely a matter of waiting. For shallow dives (less than 100 feet below the water surface), problems of gas accumulation are not an issue. Deeper dives require periods of underwater decompression in order to avoid problems.

#### Why It Matters

• Scuba diving is enjoyed by many people around the world. When they dive, they will usually breathe compressed air (approximately 78% nitrogen and 21% oxygen). At atmospheric pressure, the oxygen is used by the cells and the nitrogen is exhaled since the body does not use this gas. However, under water, the pressure is such that the nitrogen is not cleared from the tissues quickly, so it accumulates. The deeper the dive, the more of a problem this becomes. If the diver has to decompress quickly, the nitrogen comes out of solution too rapidly to be dissipated through normal breathing and complications occur.
• Hyperbaric chambers have been used for purposes other than decompression sickness. Infected wounds may benefit from increased oxygen in the system. Bone infections represent a significant challenge due to the lower blood flow to this tissue. Elevated oxygen levels can be of help in treatment of this problem. Elevated oxygen can be of benefit in cases of gas gangrene and other types of tissue decay.
• Credit: Steve Simpson
Source: http://www.flickr.com/photos/commercialdivingequipment/6004402411/
License: CC BY-NC 3.0

The interior of a hyperbaric chamber [Figure2]

• In cases of carbon monoxide poisoning, a hyperbaric chamber can be of benefit. Hemoglobin is the molecule in blood that transports oxygen from the lungs to the cells. Carbon monoxide (CO) binds to hemoglobin much more strongly than oxygen does, blocking oxygen transport. By increasing the oxygen concentration through higher oxygen pressure in the environment, the CO can gradually be displaced.

#### Can You Apply It?

Use the links below to learn more about scuba diving and hyperbaric chambers. Then answer the following questions.

1. Why is hydrostatic pressure greater than atmospheric pressure?
2. What happens when a scuba diver has to return to the surface rapidly?
3. Why are nitrogen bubbles a major concern during decompression?
4. Who first learned that nitrogen bubbles form in tissues during rapid decompression?
5. What are some causes of carbon monoxide poisoning?

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