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Was sind Teilchenzahl und Stoffmenge? I musstewissen Chemie

Mar 11, 2024
Welcome back to “mustewissen Chemie”. Today everything about the number of particles and the amount of substance. Come on. Do you know him? A Rubik's cube consists of 26 parts. It is quite complicated to solve these cubes because there are 43 billion different positions that the pieces can be rotated into. 43 billion, that's a 43 with 18 zeros after it. If you think that's a big number, that's nothing to chemists who work with molecules and atoms. We have already analyzed the size and mass of atoms. If you want to see it again, here it is. Today we talk about quantities of atoms that are unimaginably large even in the smallest portions of matter.
was sind teilchenzahl und stoffmenge i musstewissen chemie
For example, this little piece of aluminum foil. This is only one square centimeter. Not exactly impressive. But in this small piece there are approximately 60 times 10 to the 18th power of aluminum atoms. And in this drop of water there are about 33 times 10 to the 20th power of water molecules. These number monsters have incredibly long rat tails filled with zeros. They are in the range between ten billion and ten billion. You can't even imagine that. Well, how can you determine the number of particles? Counting doesn't work. But it weighs! In our video on the mass of atoms we discover how we determine the mass of atoms or molecules.
was sind teilchenzahl und stoffmenge i musstewissen chemie

More Interesting Facts About,

was sind teilchenzahl und stoffmenge i musstewissen chemie...

Don't hesitate to take a look again. If we know how heavy a molecule is, then we just need to weigh our material and then we can calculate how many molecules the material is made up of. The principle is this: let's imagine that we have several pieces of corn. To determine how much corn is here, you can obviously count them. But I could also tell you that I weigh around 50 kilos. You could then put all the corn on a scale and calculate the amount of corn based on the total weight. So, if 500 kilos come out here, you just have to divide 500 kilos by 50 kilos, that is, the weight of a mayo.
was sind teilchenzahl und stoffmenge i musstewissen chemie
Then you discover that there are ten corn here. This seems a bit complicated in the case of corn ten, but once we deal with tiny atoms and huge quantities, this approach becomes quite practical. In our last video we learned that the masses of atoms or molecules are given in the unit u. This is defined as one-twelfth the mass of an atom of the carbon isotope C12. You can convert u to grams using the conversion factor 6.022 times 10 to the 23rd power. If you want to convert u to grams, you must divide the value by 6.022 times 10 to the 23rd power.
was sind teilchenzahl und stoffmenge i musstewissen chemie
And if you want to convert grams to u, you must multiply the value by 6.022 times 10 to the power of 23. Just like in our example with the ten kernels of corn, I can now calculate how many aluminum atoms are in this ball of aluminum foil. This is how much one gram of aluminum foil weighs. A look at the periodic table tells us how much an aluminum atom weighs, that is, rounded 27 u. In principle, we only have to divide one gram by 27 u. We can only do this if we have the same units. So we quickly convert grams to u.
That means: I round the factor here, for the sake of simplicity. That's 6 times 10 to the power of 23 u. Now we divide that by the mass of one aluminum atom, so: That gives: In my hand I currently have 2.2 times 10 to the power of 22 aluminum atoms. Then I can solve it without counting. Just weighing and using my periodic table. Now you might notice something. It is quite complicated to deal with such large numbers. We had the exact same problem with the dough in the last video. Only then were the figures not impractically large, but rather impractically small. That is why we do not use the unit gram, but the unit u to express the mass of particles.
And numbers like these show us that we need an extra chemical unit that is a little more practical not only for mass, but also for quantity. And the good thing is that we already know the mole. At least its numerical value. One mole is defined as: 6.022 times 10 to the power of 23 particles. You see, this value plays an important role in chemistry. Just as a pair of shoes represents two shoes, or a six-pack of bottles represents six bottles, or giga times gigabytes represents a billion bytes, so mole represents 6.022 times 10 to the power of 23 particles. It doesn't matter what type of particles they are, whether the substance is called hydrogen, xenon, iron or glucose.
One mole of this is always 6.022 times 10 to the power of 23 particles. One mole of corn would be 6.022 times 10 to the 23rd power of corn. Let's go back to that aluminum foil. If I have a gram of aluminum foil here, then I have 0.04 moles of aluminum here. Sounds more practical than this many atoms, right? But this does not mean anything other than that: in chemistry the number of particles is abbreviated with the variable N. The number of particles has no unit. It simply describes the pure number of particles. So in our case, the aluminum foil has this many aluminum atoms.
Since the number of particles is always so large, in chemistry we prefer to use the so-called quantity of substance. This means that we are dealing with smaller numerical values, which makes everything more practical. Of course, the number of particles and the amount of substance are closely related, since in principle they describe exactly the same thing. It is very similar to the atomic mass u and grams, you can convert them together using the constant 6.022 times 10 to the power of 23. You can do the same with the number of particles and the amount of substance. The appropriate equation looks like this: n is the amount of substance.
NA represents Avogadro's constant. Again it has the numerical value 6.022 times 10 to the power of 23 and the unit is 1/mol. If we want to convert the number of particles into the amount of substance, we have to divide the value by Avogadro's constant. And if we want to convert the amount of substance into the number of particles, we have to multiply the value by Avogadro's constant. After the atomic mass and the amount of substance, in the next video we will focus on the third important quantity, the molar mass. Then you will have everything together to happily do the calculations.
By the way: In the United States, chemists and their chemist friends celebrate Mole Day on October 23. And it starts at 6:02 in the morning. Because? Americans always write the month first and then the day for their date. So if you first write the time 6.02 and then the date, it says: Basically, 6.02 multiplied by 10 to the power of 23. Maybe you can join the celebration next October 23rd. I hope you learned something new today. If yes, give it the thumbs up. If you have any questions, leave them in the comments. If you want to continue watching Chemistry, don't forget to subscribe.
Until then. Subtitles commissioned by ZDF for funk, 2018

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