If you have already decided that you will never understand stoichiometry equations, then you are already toast. There is no hope for you because you already made up your mind. But trust me, it is not that hard.
If a doofus like me can understand it, then you can too. Ideal stoichiometry only has four shapes or patterns of problems. Moll to moll, moll to mass, mass to moll.
or mass to mass. If you can only grasp these four types of stoichiometry problems, you will be in a very good shape. If it ends in metri, it means what?
Measurement. And think of stoichiometry like baking. Please watch the videos in this chemistry quick review playlist in order. Let's start by answering the question of last video.
What's the correct name of this substance? COCl2.6H2O. Please pause and try to answer this yourself.
Remember uppercase C uppercase O is carbon monoxide. However, uppercase C lowercase O is cobalt. Cobalt followed by chlorine is cobalt chloride not chlorine because that's a compound.
But do we have more than one type of cobalt? Of course, we have cobalt Roman numeral two and cobalt Roman numeral three. Cobalt 2 is divalent, but cobalt 3 is trivalent.
And since chlorine is monovalent, the one is here and not written, cobalt here is divalent because I see 2 here. So this is cobalt, Roman numeral 2, chloride. Am I done yet?
No. I have 6 waters after a dot, so it's a hydrate. How many water molecules? 6. So this is hexahydrate.
So the final answer is... cobalt, roman numeral 2, chloride, hexahydrate. Hydrates and anhydrous crystals were discussed in the last video with their problems and solutions.
Today it's time to talk about stoichiometry. Stoichio means element, which is the most basic form of matter, and metri means measurement. Have you ever heard of the philosophy of stoicism, which is the exact opposite of epicureanism? If so, what does it remind you of?
Oh, something basic, elemental, keep it simple. Who knows if anything is good or bad? Epicureanism, however, is the exact opposite. Let us eat and drink, cause tomorrow we shall die. Only medicosis can make general chemistry so profound.
As the famous late historian Will Durant once said, quote, a nation is born stoic and dies epicurean, unquote. Stoichiometry is just like baking. If in order to make one cake I need one pound of flour, one pound of sugar, and four eggs, I will make one cake.
But what if I have only half a pound of flour, half a pound of sugar, and two eggs? Can I make an entire cake? No.
Can I make half a cake? Yes. This is all about stoichiometry.
Measuring the elements, measuring the ingredients to get a certain product. But what if I have double the amount of flour, double the sugar, double the eggs. You can make two cakes. Stoichiometry is the exact same concept.
Nothing more, nothing less. So if you want to master the subject of stoichiometry, you need to acquire just five skills. That's it. First, how to balance the chemical equation, and we talked about this before in this chemistry quick review playlist. How to figure out the stoichiometric coefficients, and you can only do this after balancing the chemical equation.
Next, to figure out mole ratios. After this is to understand the difference between ideal stoichiometry and limiting reactant stoichiometry. In today's video, we'll talk about ideal stoichiometry, and in the following video, we'll talk about limiting reactant stoichiometry.
After that, the subsequent video will be about solving as many stoichiometry problems as humanly possible. If you just watch these three videos, I promise you, you will cruise through stoichiometry like a sharp knife through warm butter. In Ideal Stoichiometry, today's topic, we'll learn four patterns of problems. Mole-to-mole conversions, just one step. The easiest type of stoichiometry problems.
If you get one of these on your exam, you should leave the exam room, go outside, dance for a while, and then come back to solve the problem. That's how good they are. They are so simple.
Mole-to-mass and mass-to-mole take two steps to answer. Mass-to-mass, that's the boogeyman. You need to leave the exam room, go outside, start to weep, cry, cuss, sprinkle some dust particles on your forehead, as they did in the good old days, and then come back to try to answer these questions.
Just four patterns of problems. Even a child can recognize four different patterns. Oh, that's a puppy, that's a horse, that's an elephant. And that's a giraffe.
But first things first, if your equation is not balanced, there is no hope for you. Guaranteed to answer the question incorrectly. So the first skill is to balance the chemical equation.
Please pause and try to balance this thing. Let's do it. Start with the silicon. Okay, how many silicons do we have here?
Just one. And on the other side, also one. So we're good.
Let's look at the next one. Chlorine. I have four chlorine atoms here.
And just one chlorine atom here. Okie dokie. Let's multiply this by 4 and see. How many chlorine here?
I have 4 atoms and 4 atoms. So we're good. Let's look at hydrogen. Here I have 2 hydrogen atoms. But here I have 2 plus 4 is 6. Oh, so how can I make it balance?
Let's multiply this by 3. So here I have 6 hydrogen atoms. And 2 plus 4 is 6 hydrogen atoms. So hydrogen is good. Let's look at oxygen.
I have 3... oxygen atoms here and three oxygen atoms here. Voila!
My chemical equation is balanced. Balancing the chemical equation will enable me to get the coefficients right. So after balancing this equation, can you tell me what are the stoichiometric coefficients in this lovely balanced chemical equation?
Please pause and try to answer this yourself. Okay, so it's very easy. Basically, the coefficients are these numbers.
Okie dokie! So here I have 1, which is not written, 3, and then I have 1, I have 4. So the stoichiometric coefficients in the equation are 1, 3, 1, and 4. How about this question which we have reviewed before? What are the stoichiometric coefficients in the aforementioned equation when it's balanced? So let's go. Pause and try to answer this yourself.
Let's balance the equation. How many silvers here? Just 1. How about here? 2. So if I try to multiply this side by two, I'll have two iodines, but I have three iodines here. Oh, two versus three.
What do you do? Well, whenever in doubt, you place a six here. Why? Six iodines. Amazing.
And to make the six, you multiply this by two. Let's see if the iron is balanced. I have two iron atoms here and two iron atoms here.
Amazing. Iodine. Six iodines and six iodines. Silver. Six silvers and two silvers.
How about multiplying this by three? Now I have six silvers and six silvers. Mr. Carbon, I have three carbons here, and on the other side I have three carbons there. Perfect.
Oxygen. Three times three is nine oxygen atoms, and three times three is nine oxygen atoms. This is my balanced chemical equation.
Now what are the stoichiometric coefficients? Six, one. 2 and 3. So the correct answer here is E, as in E equation. After mastering the first two skills, let's talk about skill number three, mole ratios. Take a look at this wonderful equation that we have just balanced.
We have reactants on this side and products on the other side. And the arrow means yields. The reactants react together to yield the products. Let's suppose that this is A, this is B, we'll call this C, and this one is D.
I can get any ratio I want. I can get A to B, which means 6 moles of AGI to 1 mole of Fe2CO3, all three. How about A to C?
Sure, put the 6 moles of AGI on the numerator and the 2 moles of FeI3 in the denominator. How about A to D? We can do this as well. 6 moles to 3 moles.
How about B to C? Similarly, we can do this. You can do any ratio you want. So we have six possible ratios, and these ratios will be exploited by your professor in your exam.
Next is to understand the difference between ideal stoichiometry and limiting reactant stoichiometry. Ideal means ideal conditions in La La Land that does not really exist. It assumes that we have everything in the perfect most abundant proportions.
We will not run out of any ingredients. i.e. reactants. No loss of reactants and 100% yield for products. Everything is hunky-dory.
However, in reality, most reactions are limiting reactants to a geometry. Assuming more realistic conditions, not this la-la land, only some reactant molecules go through the chemical reaction and yield not 100% of the product, but we'll assume most of the products. We did not start with enough ingredients. We ran out of one of those reactants first, which limits the amount of the products formed. Example, I expect to make one cake, so I want one pound of flour, one pound of sugar.
Okay, I have those. Let's look in my refrigerator. I did not have four eggs. I only had two eggs.
Oh, that's a limiting... reactant. With this in mind, do you think I'll be able to make an entire cake?
No, you will not make 100% of the cake, because your reaction was limited by one reactant. Now let's get real. Butyric acid, also known as butanoic acid, C4H8O2, is aerobically metabolized.
We'll assume that carbon dioxide and water are the only products. Please write down the balanced chemical equation and the stoichiometric coefficients of each agent. Please pause and try to solve this yourself.
Remember from biochemistry, what does aerobic metabolism mean? If you've watched my biochemistry playlist or my biology playlist, you know that aerobic metabolism meaning metabolize something in the presence of oxygen. To yield what?
Carbon dioxide and water. This metabolism happens every day in your body, but we do not start with butyric acid, instead we start with glucose most of the time. And your cells will release carbon dioxide, which you exhale.
And water in many forms, such as water vapor, you will exhale this as well. And just good old water, which you will urinate and or sweat, etc. So this is my equation before balancing. Let's balance the equation.
Okie dokie, it becomes like this. Four carbons on this side, four carbons on this side. Eight.
hydrogens on the side, 4 times 2 is 8 hydrogens on the side. 2 oxygens here and 10 oxygens here is 12. And I have 4 times 2 is 8 oxygens and 4 oxygens, also 12. So I just balanced the equation. What are these two ekiometric coefficients of each agent? I have 1, I have 5, I have 4, and 4. Using the same equation that you just balanced. In an ideal reaction, i.e. ideal stoichiometry, assuming everything is hunky-dory and we're not running out of anything, if 4.25 moles of oxygen react, how many moles of carbon dioxide could be formed?
Please pause and try to answer this yourself. The reason you're struggling with stoichiometry is because you haven't organized your thought. There are only four possibilities.
They can ask you mole to mole or mole to mass or... mass to mole or mass to mass. Mole to mole is just one step. Mole to mass and mass to mole, two steps each.
Mass to mass is the horrible one, three steps. Regardless of the methodology, regardless of the pattern, we can follow these steps. Thank you again, the great teacher Julie C. Gilbert and her wonderful book, Five Steps to Surviving Chemistry. Step number one, start with the given info.
And then, dimensional analysis time, you set up a conversion factor ratio. Whatever you're starting from goes in the denominator. Whatever you're aiming at, whatever you're converting to, goes in the numerator.
And then you cancel top, bottom, etc. Repeat step number two as many times as needed. Sometimes we repeat it once, mole to mole conversions.
Sometimes we repeat it twice, mole to mass or mass to mole. And sometimes we do the same thing three times, mass to mass problems. Do the math, cancel top and bottom, and then give me your numerical value, and don't forget the measuring unit.
We will use these steps to answer and solve this problem. Let's go. 4.5 moles of oxygen react.
Then how many moles of carbon dioxide could be formed? Now, do you think this is mole to mole, mole to mass, mass to mole, or mass to mass kind of problem? Let's see.
Moles of oxygen. and moles of carbon dioxide. This means mole to mole conversion. And if it's mole to mole problem, we only need one step. Woohoo!
This is easy. So let's follow the methodology. Step number one, you start with the given.
Okay, what's the given? 4.25 moles of oxygen. Okie dokie. And then what?
You start to aim at carbon dioxide. So let me set up a dimensional analysis conversion factor ratio. Let me put mole of oxygen downstairs so that I can cancel this with this. I know that by looking at this balance equation, that 5 moles of oxygen here will yield 4 moles of carbon dioxide. Absolutely.
So what? Now I can cancel this with this. And my end result will be moles of carbon dioxide, which is what they want.
So you just multiply 4.25 times 4 divided by 5. So the answer will be 3.4 moles of carbon dioxide. For the excellent student, we'll look here. 4.25, how many significant figures? Three.
So let's add a zero to make our answer in three significant figures. I converted mole into mole. Bingo. And here's the same answer in color.
First, you need to balance the equation. Next, you need to recognize that this is mole to mole stoichiometry problem, which means just one step. And then dimensional analysis.
I see. Start with the given, which is the number of moles of oxygen, and then set up a conversion factor, moles of oxygen downstairs and moles of carbon dioxide upstairs, because the answer has to be in moles of carbon dioxide. You cancel top with bottom, you do the math, 3.4 at the zero, moles of carbon dioxide.
Bingo! That's the easiest stoichiometry problem. Let's take it up a notch. Same equation here. If five moles of oxygen react, how many moles of carbon dioxide should be formed?
Please pause and try to answer this yourself. Are you done? Let me show you how most of you answer this. You said let's start with the given, which is five moles of oxygen, and then I multiply this by, I have to put moles of oxygen downstairs, and I know that five moles of oxygen will give me four moles of carbon dioxide.
and then you cancel moles of oxygen with moles of oxygen, the 5 with the 5, and your end result is 4 moles of carbon dioxide. This is correct, however, you could have saved a lot of time by recognizing that this 5 moles of oxygen is already written here. And since my equation is balanced, the answer has to be this 4 moles of carbon dioxide. Bingo!
If your equation is balanced, the 5 moles of oxygen will react with this doofus to give you 4 moles of carbon dioxide. Voila! Chemistry makes so much sense once you understand what the flip you're talking about, instead of just memorizing like a freaking donkey.
Forgive my language, just get excited. Here is another question. If 4.25 moles of oxygen react, how many grams of carbon dioxide could be formed using the same equation? Please pause.
First order of business, balance the equation. It is balance. Second order of business, we need to recognize that this type of problem is mole to grams.
It's mole to mass, which means two steps. Okay, let's go to town. I start with the given 4.25 moles of oxygen, and then I multiply this by, I have to put moles of oxygen downstairs, and I know that five moles of oxygen will yield four moles of carbon dioxide, which is right here. And then what? I can cancel moles of oxygen with moles of oxygen.
But this will give me the answer in moles of carbon dioxide. Do I need the answer in moles of carbon dioxide? No, I need the mass of carbon dioxide, grams. Easy. Can you convert moles to grams?
Sure. Put moles of carbon dioxide here downstairs and look at your periodic table. One mole of carbon dioxide has one carbon atom and two oxygen atoms.
One carbon atom has 12 AMU or 12 grams and 2 oxygen atoms means 2 multiplied by 16. Then I cancel moles of carbon dioxide with moles of carbon dioxide. The rest is math history which will give me the answer in grams. The answer is 149.6 grams of carbon dioxide. Is this what they wanted? Yes.
But an excellent student will take a look at this number. Three significant figures. Oh, here I have four.
Well, let's make them three. How do I do this? Well, you just take care of the six.
So instead of 149, do not make it 149. You make it 150 grams of carbon dioxide. And that's your final answer. This is how to solve mole-to-mass stoichiometry problems. Same answer in colors. I recognize that this is mole-to-mass.
After balancing the equation, I'm ready to go. 4.25 moles of oxygen upstairs. Put moles of oxygen downstairs to cancel one another. And then 5 moles of oxygen will give me 4 moles of carbon dioxide. But I'm not done yet because I want my answer in grams, not moles.
I know that 1 mole of carbon dioxide will contain 1 times 12, which is 12, plus 32, which means 44 grams of carbon dioxide. Then I can cancel moles of oxygen with moles of oxygen, and moles of carbon dioxide with moles of carbon dioxide, and the result will be in grams of carbon dioxide. Bingo. Let's take it up a notch.
Here is the same equation. But a different question. 50.5 grams of oxygen react. How many molds of water could be formed? Please pause and try to solve this yourself.
Let's talk about this. Is my equation balanced? Yes. They want grams to moles.
Oh, so mass to moles. Also two steps. Now I'm ready.
Let's go to town. 50.5 grams of oxygen because I start with what I have. Then I put grams of oxygen downstairs in order to cancel grams of oxygen with grams of oxygen. I know that one mole of oxygen contains, look at your periodic table, two oxygens, 16 and 16. So 32 grams of oxygen.
Okay. How can I cancel moles of oxygen? Because if I just go with this, I'll get the answer in moles of oxygen, but they want moles of water.
Easy. You put moles of oxygen here downstairs. And you look at the equation. I see here that 5 moles O2 will give me 4 moles of water.
Amazing. Then you cancel moles of oxygen with moles of oxygen, and the end result will be in moles of water. Just do the math, and the math will give you 1.26 moles of water.
Is this what they wanted? Yes, it is. Three significant figures, three significant figures, we're done. The answer in color.
First, balance the equation. Second, recognize that this is mass to mole conversion, which means it's just two steps. Let's go. You start with what you have, grams of oxygen.
Let's put grams of oxygen downstairs to cancel. One mole of oxygen has 32 grams of oxygen. And then you put the moles of oxygen downstairs.
Look at the equation, five moles of oxygen. will give me 4 moles of water. Cancel, cancel, cancel, and you get 1.26 moles of water.
Yet another question. Same equation, different question. If 50.5 grams of oxygen react, how many grams of water could be formed?
Please pause and try to answer this. First, my equation is balanced. Next, grams to grams.
So this is mass to mass stoichiometry problem, meaning it will take me three steps to complete. Oopsie. We can do this, folks.
50.5 grams O2. I start with what I have. I need to cancel with grams O2.
I know that one mole of oxygen from the periodic table contains 16 plus 16, which means 32 grams of oxygen. Now I can cancel grams of oxygen with grams of oxygen. Now what?
Do I need the answer in moles of oxygen? No. We still have two steps left.
What should I do next? I can cancel moles of oxygen with moles of oxygen. So I put moles O2 here.
I know from the equation that 5 moles of oxygen will give me 4 moles of water. So I put the 4 moles of water right here. Cancel the moles of oxygen with moles of oxygen. Do I need my answer in moles of water?
No, I need it in grams of water. Oh, so moles to grams. I can put moles of water downstairs so that I can cancel it with moles of water upstairs. I know that 1 mole of water contains 2... hydrogens, so 2 times 1 gram from the periodic table, plus 1 oxygen, which means 1 times 16. 2 multiplied by 1 is 2, plus 16 is 18 grams of water.
And then everything is cancelled. You just multiply this number by 4, you multiply this by 18, over 32 times 5, and we get the answer of 22.725 grams of water. and they want the answer in grams of water. An excellent student will take a look here.
50.5, three significant figures. So I need only three significant figures, which means 22.7 grams of water. That's the answer.
Same answer in color. Look at the equation. Is it balanced? Yes.
Then recognize the pattern. Oh, this is mass to mass stoichiometry problem, which means three steps. You start with what you have, and then I know that grams of oxygen can be put downstairs.
one mole of oxygen has 32 grams of oxygen then i can cancel this with this one mole of oxygen has to cancel with moles of oxygen i know that five moles of oxygen will yield four moles of water then i can cancel four moles of water with mole of water how do i do this i know that one mole of water contains 18 grams of water then you cancel grams of oxygen with grams of oxygen mole of oxygen mole of oxygen mole of water mole of water your end result will be in grams of water And this is how to perform the most difficult stoichiometry question, which is mass-to-mass stoichiometry problem. Mole-to-mole problems, just one step. Mole-to-mass or mass-to-mole, two steps each. But mass-to-mass is three steps.
In this video, we learned how to balance the chemical equation, how to figure out the coefficient of stoichiometry based on the balanced chemical equation, how to figure out the mole ratio, for example, by relating oxygen from the reactants with water from the products. You can also relate the two reactants together or two of the products together. Then we learned that in real life, most reactions are limiting reactants to ichiometry, but today's problem were about ideal stoichiometry.
which means we never ran out of anything. In the next video, I'll show you limiting reactants to a geometry where you will run out of one of the reactants first, and you will not yield 100% of the products. Can you answer the following question?
If the average human body contains 25.00 moles of calcium, question 1, what's the number of calcium atoms in the average human body? Question 2, what's the number of moles of calcium in a sample that has 5.00 times 10 raised to the 24th? power atoms of calcium? Let me know your answers in the comments. And here is another question.
Here's the equation. What's the stoichiometric amount in grams of oxygen needed to react with 2.50 grams of aluminum in the aforementioned equation when it's balanced? Let me know your answer in the comments.
You'll find the answer key to these two questions in the next video, where we talk about limiting reactants to a geometry. If you find my videos helpful, please consider buying me a coffee or downloading my notes from my website. I have chemistry notes, biology notes, biochemistry notes, physiology notes, all kinds of notes at medicosisperfectionaries.com.
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