Application Of The Mole
Previously we looked at why we need the concept of the mole in chemistry. And what the mole is in this movie. We apply this knowledge to help consolidate our understanding of the sinful concept. I want to understand how the mole helps us plan our rocket launch. But first let's apply what we learned in the previous movie to compounds. Oh, yeah, we only used examples of elements before does the mole also work with compounds.
It does indeed so let's take carbon dioxide. As an example, what do you know about. A molecule of carbon dioxide. And what do you know about a mole of carbon dioxide molecules? Let me think before we get to that click on the link below for a self-marking quiz as well as the mind map that we use complete the quiz to check your understanding and make the process more interactive, you'll also see a timeline of this movie so that you can easily jump to places you need to re-watch, please also like and subscribe and press the bell and check out my website, learn science.coma there. You can.
Also order a poster of this mind map and the workbook and teacher guide which it comes from carbon dioxide, c, o. T, here's, a sub microscopic representation of a co2 molecule. Count the nucleons in this picture. I already know it's 12 in carbon, which also matches carbon's mass number on the periodic table, 16 in each oxygen atom, matching oxygen's mass number so that's, 12, plus 16, plus 16. And in my calculator here we are looking at carbon dioxide on the sub microscopic level, 44 so what's, the mass of one. Molecule of co2 44 44.
What is it grams or is it ammo we're speaking about a molecule? So that's really light. So it must be the light unit amu. Now, if you could count out six commas zero, two times 10 to power, 23, such co2 molecules, what would its mass be also 44? Yes, but 44?
What 44 grams that's right? So we see that even if we're speaking about compounds mass numbers from the periodic table are reusable as both the submicroscopic mass measurements in ammo per molecule and of the macroscopic molar mass. In grams per mole for that substance. What if I want six comma zero two times ten to power, twenty-three molecules of water? What do I do?
Well, that's a mole of water and water's formula is h2o. So one molecule of water is two h's and one o. And each h has one nucleon and o has 16 nucleons. So one molecule of water has one plus one, plus sixteen, 18 nucleons.
And so that weighs 18 ammo and a whole mole of those molecules also weighs 18, but now it's, 18 grams. And so I weigh out 18 grams of water. And I give. That to you and voil, 6.02 times 10 by 23 molecules of water by weighing it I'm, actually, counting it correct, although you should actually say mass, not weight because weight is measured in newtons, not grams by getting mass I'm, actually, counting that's right? So the mole concept links the sub microscopic and the microscope. Okay. So now I want to know about our rocket problem when I'm planning how much oxygen and hydrogen to put together in my rocket.
Yes. So the trick is that we need to figure out how. Much hydrogen and oxygen to put in the rocket. So they react with one another completely. So none is left over unreacted at the end.
Well, a water molecule is h2o. So we need double as many h's as those. So what if we have Avogadro's number of o atoms, how many h atoms do we require two times Avogadro's number say that in another way for one mole o atoms, we need two moles, h atoms. Okay. So we know we require double as many moles of hydrogen atoms as oxygen atoms, but that isn't the same thing as double as many. Grams of hydrogen as oxygen, why not, of course, moles is how many five grams is how heavy, so we're not referring to how much in the same way and a hydrogen atom, doesn't, weigh the same as an oxygen atom.
Okay? So what we're going to do we go to the periodic table. And we look up the mass of a mole of hydrogen atoms, one gram and the mass of a mole of oxygen atoms.
16 grams good from this. We can calculate the mass of two moles of hydrogen atoms, two times one gram equals two grams. So now convert the two.
Mole hydrogen is to 1 mole. Oxygen particle ratio into a mass ratio 2 grams h is to 16 grams o. Yes and what's.
The advantage of each of these ratios. Well, the particle ratio is easier to think about when I think about a water molecule. And the mass ratio I could actually go and measure out 2 grams, hydrogen and 16 grams of oxygen. And then I mix them together. And then I'd know that when they react there's going to be just the right amount that every oxygen can get its two hydrogens. So that then. There's not going to be anything left behind afterwards.
I hope you realize that 2 grams hydrogen, plus 16 grams, oxygen isn't. The only combination that has the masses just right so that the reaction happens with no unreacted hydrogen. Why? Because this is a ratio. So it tells us the relative masses, not necessarily the actual is needed. So that neither reactant will be in excess.
Oh. So, like if I had 4 grams, hydrogen and 32 grams oxygen or 20 grams, hydrogen and 160 grams oxygen and 2 million grams of. Hydrogen, plus 16 million grams oxygen and so on.
Then they'd also just react right and then there'd be no hydrogen and no oxygen left. So you see that we've used the concept of the mole to help us to convert the particle ratio to h is to 1o to the mass ratio to grams h is just 16 grams o in so doing. We've solved the problem that we think about chemistry well in particle ratios in which we refer to sub microscopic particles, but we work practically with chemicals on the macroscopic scale, where.
We need to use a practical variable like mass. So we've bridged the gap between the submicroscopic and the macroscopic using the mole cool, but wait isn't there something wrong with the whole way that we did that. Because this is the balanced equation for the reaction of hydrogen and oxygen to make water. Okay, let's. Look at it. All again, from this perspective, the chemical equation gives the particle ratio in which the chemicals react. So what does this equation?
Tell you it tells me that we need one. Oxygen molecule, which is diatomic, there are two atoms bonded together to make this molecule. Okay, so we require one of those to react with two hydrogen molecules. Hydrogen is also diatomic, yes. And then when they react, the two atoms in each molecule, break apart, and then those three atoms rearrange, and we have water two waters, two water molecules, yes, although you should realize that this is a ratio. So you should actually say for every one oxygen molecule, two hydrogen molecules, react to form two. Molecules of water, in fact, it would almost never be really only two h2s and one o2 and two h2o molecules.
Okay. So like it could be 10 02s with 20 h2s to make 20 hos and 200 o2s with 400 h2s to make 400 hos and a million o2s with 2 million h2s to make. Yes.
You could go on forever with examples, which are all in this ratio, would it be right to say, one gram o2 for 2 grams h2 to create 2 grams h2o that would be mixing up particle and mass ratios that would be mixing up how many with how heavy right. What about six comma zero two times ten to the power, twenty-three o2 that's, how many, so we can use the same ratio? Okay? So that's Avogadro's number of o2s. So we'd need two times Avogadro's numbers of h2s.
And that would give us two times Avogadro's number of h2o say that in another way, one mole o2 reacts with two moles h2 to form, two moles, HDL, correct since molecules are particles and moles of molecules are groups of particles. And the balanced equation gives the particle ratio. We can think about. This equation, both on the submicroscopic level and the macroscopic level, but make sure that when we do that we are thinking about counts of how many not masses, okay, but we require masses to be able to weigh out the right amount for our rocket. Yes. We do.
So now we convert this molar particle ratio into a mass ratio. Okay. So the molar mass of o2 is 16 times 2, which is 32 grams per mole. And the molar mass of h2 is one times two that's, two grams per mole. But remember, the particle ratio is one mole o2 for. Every two mole h2, okay.
So two moles h2 is two times. Two grams is 4 grams. And the molar mass of h2o is 18 grams, and we require 2 moles of fat. So that's 36 grams. So how do we change?
The particle ratio of one mole o2 is to two mole h2 is to two moles h2o to a mass ratio. 52 grams o2 is 24 grams. H is 236 grams, h2o. Okay.
So I'm this way out 30 grams of liquid oxygen and four grams of liquid hydrogen. And then they react together, boom and that'll be just the right amount of oxygen for hydrogen. And then. There'll be nothing left. Well, there'll just be water.
Left that's, one option. But any masses in the same ratio as this would do the trick too. And how does the answer we get thinking it through from the balanced equation? Compare to the answer that we got when we just thought about the formula of water?
Oh, yeah, that time we said, we need 16 grams owed for every 2 grams aged. And now we said, 32 grams o2 4 4 grams h2. The second answer is double the first one, so they're in the same ratio and since we're. Looking for the ratio, the relative numbers, can you see that we actually found the same answer using the two different methods? Actually they both eight grams o2 for every one gram, h2 that's, the way to write them in the simplest ratio right at the beginning of this three-part series?
I said that there are two keys to understanding stoichiometry. The first has to do with the mole concept. The second has to do with the use of proportion in other words, how to use ratios like this one to work out how. Much of a certain chemical we need or produce when we're given information about another chemical click here for help on that, and you'll see when you do that it's almost impossible to use proportion correctly in stoichiometry.
If you don't understand what we've been discussing in the past three movies, finally, a reminder about the free south marking quiz given in the link below and don't forget to like and to subscribe. And in the comments below how much space would a mole of balloons takes up alone. How high would a mole of five cent pieces reach? What could you buy with a mole of five cent pieces? I wonder how much science could you learn in a mole of second? I could become a genius.
Hopefully we meet again way before then I think we're better foreign.