How Many Moles Are in One Liter of Water?

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You can find out how many moles are in one liter of water by using a very particular equation in the right way. Find out how many moles are in one liter of water with help from a research scientist and one of the world's leading experts on star formation in this free video clip.

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Video Transcript

Hello, my name is Harold Yorke. I'm a research scientist in Pasadena, California. Let's talk about how to determine how many moles there are in one liter of water. When a chemist talks about a mole he is saying this is a certain number of molecules or atoms. And that number is 6.022. I would have to continue and write another 20 zeroes behind these 4 digits, but instead I'm going to use scientific notation. So I put a decimal point behind the zero times 10 to the 23. This is the number of atoms or molecules in a mole. It's defined by taking 12 grams of carbon and the number of carbon atoms in that 12 grams. And of course it's a special type of carbon. it's a carbon called Carbon - 12 that has exactly 6 protons and 6 neutrons in the nucleus. There's other forms of carbon like carbon 13, carbon 14 but it's defined as 12 grams of carbon 12. That's the number. Now the next thing I have to define is a liter. A liter is a volume of a material that has dimensions 10 centimeters x ten centimeters x 10 centimeters. It's a cube and it's equal to exactly 1 liter of water is 1 kilogram or 1000th grams. I'm changing to grams because we'll see the gram weight of a mole. The next thing I need to know is the chemical formula for water. H2o. This means if I have a mole of water I will have a mole of oxygen and 2 moles of hydrogen. So lets look up. If I have a mole of oxygen what is its weight or mass in grams? Well carbon 12 had 12 grams oxygen, a mole of oxygen would have 16 grams. Hydrogen has the atomic weight of 1. That means we would have, since we have two of them, 2 moles of hydrogen would have 2 grams of mass. So the total of a mole of water, 1 mole of water is 18 grams. So I decided to clean up the white board and actually write out the number of molecules in a mole. With all the 20 zeroes. So now lets do the math. We have 1000 grams of water and 18 grams per mole. The answer is 55.6 moles of water in 1 liter. Thank you.


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