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Dalton's Law - Concept

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Teacher/Instructor Kendal Orenstein
Kendal Orenstein

Rutger's University
M.Ed., Columbia Teachers College

Kendal founded an academic coaching company in Washington D.C. and teaches in local area schools. In her spare time she loves to explore new places.

Dalton s Law states that total pressure of a gaseous mixture is equal to the sum of the partial pressures of each substance present.

Alright. Amongst the neat things that Dalton did for us in Chemistry, he came up with his own law called Dalton's law of partial pressure. And what that states is that the total pressure of a mixture of gas is equal to the sum of the pressures of all the gases in the mixture. Before we move on I just want to make sure we understand what partial pressure is, and that's the pressure exerted by a single gas within a big mixture of gases. Okay, this might actually be the easiest of all the gas laws that we've learned about. So let's actually put this into practice and see what it is that I'm talking about.

Alright. So at sea level we know that air, that air pressure is equals to 101.3 kilo pascals. We know that. And what does air consist of? Air consist of nitrogen, oxygen, water, vapor, argon and carbon dioxide. All these stuff makes up our mixture of air that we breathe in everyday. Okay, so we know the total pressure is 101.3 kilo pascals, we can then figure out the pressure of each individual substance. So we've nitrogen is 78.1 kilo pascals, oxygen gas is 20.9 kilo pascals, water vapor is 1.28 kilo pascals, argon is 0.97 kilo pascals and lastly carbon dioxide is 0.05 kilo pascals with at least volume this one. So all these stuff when you add up everything, would equals 101.3 kilo pascals. This is example of Dalton's law. But you can do other things with these two besides just adding up to get the total pressure. You can actually find the percentages of each one too. So if we, say you wanted the percentage of nitrogen in air, you would take 78.1 divided by our total which is 101.3 and you'd find that nitrogen can makes up 77 percent of our air.

The same way you can do with oxygen. 20.9 divided by 101.3 kilo pascals and we find that it's 20.6 percent of the air we breathe. You can do the same thing for each one and figure out the percentage of each substances in the total mixture.

so there's a lot of different fun things you can do with Dalton's law even though it actually fairly simple.