# DALTONS LAW By Raymond Greenlaw. Learning Objectives State Daltons Law Understand Daltons Law Apply Daltons Law Explain relevance of Daltons Law to scuba.

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DALTONS LAW By Raymond Greenlaw

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

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

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.

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.

Visual of Daltons Law

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.

Popcorn and Marbles Thought experiment with popcorn and marbles

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.

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?

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.

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.

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.

Questions Thanks for coming! www.raymondgreenlaw.com

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