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DALTONS LAW By Raymond Greenlaw

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Learning Objectives State Daltons Law Understand Daltons Law Apply Daltons Law Explain relevance of Daltons Law to scuba

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John Dalton English chemist Father of atomic theory Discovered colored blindness Discovered gas law in early 1800s

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State Daltons Law The total pressure exerted by a mixture of gases is equal to the sum of the pressures that would be exerted by each of the gases if it alone were present and occupied the volume.

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State Daltons Law Mathematically, P total = P 1 + P 2 + … + P n, where P i is the partial pressure of gas i. In this case we have n total gases.

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Visual of Daltons Law

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Understand Daltons Law At sea level air is roughly 20% Oxygen and 80% Nitrogren. Pressure at sea level is one atmosphere. According, to Daltons Law PO 2 =.20 × 1 ata =.2 ata PN 2 =.80 × 1 ata =.8 ata That is partial pressure of oxygen is.2 ata and of nitrogen.8 ata.

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Popcorn and Marbles Thought experiment with popcorn and marbles

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Apply Daltons Law What is the partial pressure of oxygen in air at sea level in pounds per square inch? PO 2 =.21 × 14.7 psi = 3.1 psi Note, the.21 represents the fraction of air that is oxygen at sea level.

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Apply Daltons Law Suppose the total pressure of three mixed gases above sea level is 8 psi. Suppose two of the gases have the same partial pressure and a third gas has a partial pressure of 4 psi. What are the partial pressures of the other two gases?

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Solution From Daltons Law we know that P total = P 1 + P 2 + P 3 We are told P total = 8 psi. We are told for gas three the psi is 4, so P 3 = 4. Since we are told P 1 = P 2, we get 8 = (2 × P 1 ) + 4, so P 1 = P 2 = 2 psi.

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Explain Relevance of Daltons Law to Scuba The air delivered to a diver at depth is delivered by the regulator at ambient pressure. At sufficient pressures, gases such as nitrogen, oxygen, and contaminants, can have adverse or dangerous effects on a diver. Gases breathed at high pressure will pass into solution in the bodys tissues. Gas toxicity, a dangerous condition, could result.

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References NAUI Master Scuba Diver Manual, 2010. En.wikipedia.org/wiki/John_Dalton www.thescubaguide.com Figures borrowed from around the web, please let me know if any of the figures are not in the public domain and I will replace them.

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Questions Thanks for coming! www.raymondgreenlaw.com

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