Stoichiometry Basic Introduction, Mole to Mole, Grams to Grams, Mole Ratio Practice Problems

This video will provide a

basic

introduction

to the geometry of the story and for most chemical reactions there are

basic

ally three types of conversions you need to worry about; The first type, the shortest, is to convert the

mole

s of substance A to the

mole

s of substance B and you need to identify the mole

ratio

to do that. Number one will focus on that problem. The second type of problem is converting the moles of substance A to the G of substance B or you might be given the

grams

of substance A and you need to convert it to moles of substance B, so that's the second type of problem you'll see.

The third type is if they give you the

grams

of substance A and you need to convert them to grams of substance B. This involves, I think, three steps and this two steps and the first one is a single step, so let's start working on these

problems

. Number one. Sulfur dioxide reacts with oxygen gas to form sulfur trioxide. If 3.4 moles of sulfur dioxide react with excess oxygen. As? Many moles of sulfur trioxide will be formed. The first thing we must do is write a balanced chemical equation. Sulfur dioxide is SO2, diatomic oxygen is O2 and sulfur trioxide is SO3, so now we need to balance it with the sulfur atoms.

They are balanced on both sides but we have four oxygen atoms on the left and three on the right, so let's start by putting two in front of 2, so now we have two sulfur atoms, which means we have to put two in front of 3. Now it turns out that the number of oxygen atoms on both sides is now six on this side 2 * 3 is six here 2 * 2 is 4 plus another two, that's six so we have a balanced chemical equation at this point we are now given 3 .4 moles of sulfur sulfur dioxide and we want to convert it to moles of sulfur trioxide, so what we have to do is use something called the molar

ratio

, the ratio M between sulfur dioxide and sulfur trioxide is 2 to 2, which This means that for every two moles of sulfur, carbon dioxide will now be produced that reacts with two moles of sulfur trioxide, since we have 2 moles in the upper left, we must place it in the lower right so that those units are cancel and the other two moles of SO3 we could put on top so that whenever you want to convert from moles of substance A to moles of substance B, all you need is an additional fraction beyond the one you're starting with and you'll get the answer 2 /2 is basically one, so the answer is 3.4 since the ratio M, the coefficients are the same, the ratio M is one, so this is the answer for part A based on this example.

Go ahead and try Part B. How many moles of oxygen gas will completely react with 4.7 moles of sulfur dioxide, so let's get started? With what we are given, which is 4.7 moles of SO2, we now need to convert the moles of SO2 to moles of oxygen gas, so it is a one-step problem, all we need is an additional fraction, so that we need the ratio M between SO2 and O2, for every two moles of SO2 that react, one Mo of oxygen reacts along with it, so let's put the two moles of SO2 at the bottom, but at the top we are going to put a mole of o2 according to the coefficient in front.

So make sure you balance the chemical equation before you start this problem, so the answer will be 4.7 divided by 2, which is 2.35 moles of O2. As you can see, it is not that difficult to convert moles of a substance to moles. of another substance number two, propane reacts with oxygen gas to form carbon dioxide and water, part A, if 2.8 moles of propane react with excess oxygen gas, how many GRS of CO2 will be formed? So, let's write down what we should do. They give us the moles. of propane C3 h8 and we need to convert it to the gr of carbon dioxide so basically we have the moles of substance a and we want to convert it to the gr of substance B so it's a two step process so let's take one. step by step, so starting with moles of a you want to use the ratio M to change it to a different substance while keeping the same unit, the unit is moles, the substance is a, so you want to change one thing to the time in In this first step we are changing from substance A to substance B.

Now that we have substance B, we can change the unit from moles to gr, so it is a two-step process for this problem. Now, before we can begin, let's write a balanced chemical equation. we have propane C3 h, it reacts with oxygen gas to produce carbon dioxide and water, so we have three carbon atoms on the left, therefore we need to put a three in front of CO2 and there are eight hydrogen atoms on the left and two to the right. 2 * 4 is eight, so let's put a four in front of the water. Now 3*2 is six, so we got six oxygen atoms from the 3 CO2 molecules and 4*1 is four, so we get four oxygen atoms from the four water molecules, giving us a total of 10 oxygen atoms on the right side, which means we need 10 on the left side. 10/2 is 5, so we need to put a five in front of o2, so now we have a balanced chemical equation.

Now in part A we are Given 2.8 moles of propane, we first need to convert or change the substance from propane to carbon dioxide because that is what we are looking for, so let's use the ratio M to change the substance, so the ratio M between propane and carbon dioxide is 1 to 3 so, for every mole of propane that reacts, 3 moles of CO2 will be produced in this reaction, so we can cancel these units. Now we can convert from moles of CO2 to G of CO2, so we need the mass M of carbon dioxide for CO2 to contain one. carbon and two oxygen atoms, so that's 12.01 + 2 * 16, which will be 4 24.01, so 1 mole of CO2 has a mass of 44.1 G, so whenever you see this number, the mass M, the units are G per mole, so one mole of that substance has a mass of 44 G, so now let's do the math so we can multiply it by 2.8 * 3 * 44.0 0 1 and I got 369 .50 grams of carbon dioxide, so that's it for part A.

Now let's move on to part B. You can pause the video if you want to try it. This is very similar to part A. How many GRS of oxygen gas will completely react with 3.8 M of propane? So ultimately we need to convert moles of propane to G of oxygen. So let's follow the same steps, first we need to change the substance from propane to oxygen, but keeping the unit the same, so we need to use the ratio M to change a substance, after that we could use the mass M to convert from moles from o2 to G of o2 so that is the model of what we should follow, so let's start with what we are given, which is 3.8 moles of propane and let's use the ratio M to convert it to moles of o2 to change a substance, so the ratio M is 1 to 5 then one mole of propane C3 h8 will react completely with five moles of o2 so now we are at this point so we need to use the mass M to go from moles to G now the atomic mass of a single oxygen atom is 16 so the mass M of an oxygen molecule that has two oxygen atoms is 2 * 16 or 32, so it is 32 G per mole, what that means is that 1 mole of O2 contains a mass of 32 G.

Now we can get the answer, so it's 3.8. * 5 * 32 and so that's 68 G of o2, so that's the answer for Part B. Now let's move on to part C. If 25 G of C3 h8 reacts with the excess oxygen, how many moles of water will be formed ? This time we are given the gr of C3 h8 and we need to convert it to moles of water, so we are given the grams of substance A and we need to convert them to moles of substance B, so first we need to change the unit we need to go from. GRS to moles and we're going to use the mass M to do that and then we're going to use the ratio M to change the substance from A to B, so in our particular example we're going to convert the GRS of propane. to moles of propane using the mass M of propane and then we will use the ratio M to change the substance from propane to water, so basically part C is the reverse of A and B, so let's start with what we were given. in the problem which is 25 G of propane, now we need to find the mass M of propane, it has three carbons and eight hydrogens so it is 3 * 12.01 plus 8 * 1.8 which results in 44.94 G per mole, that is, one mole of propane. has a mass of 44.0 94 grams, so we could cancel the GRS unit of C3 H, so now let's use the ratio M to change the substance from propane to water, so the molar ratio is 1 to 4, so that for every mole of propane that reacts, four moles. of water will be produced now let's perform the operation is 25 / 44.94 * 4 so this is approximately 2.27 moles of H2O and that is the answer Part D if 38 G of water are produced in the reaction how many moles of CO2 were produced this time?

We are given the grams of water and we need to find the moles of carbon dioxide, so, as before, we will first change the unit from grams to moles using the mass M and then using the mole ratio we are going to change a substance from water to CO2 , so let's get started, if you want to pause the video and work on this problem, feel free to move on because the best way to learn is through

practice

taking measurements, so let's start with 38 G of H2O and convert it. to moles, then we need to find a mass m of water, so we have two hydrogen atoms plus one oxygen atom, each hydrogen atom is 1.8, we multiply that by two and then add 16, so the mass M of water is 18.016 G per mole. so one mole of water has a mass of 18.016 G, so now we can move on to the last step and that is to convert moles of water into moles of CO2, so the molar ratio is 3 to 4, for every four moles of water that are produced.

In this reaction three moles of carbon dioxide are produced along with it so it will be 38/18.016 multiplied by 3/4 so the answer I have is 1.58 moles of carbon dioxide and that is the final answer . Aluminum number three reacts with chlorine gas. to form aluminum chloride, part A, if 35 g of aluminum reacts with excess chlorine, how many grams of aluminum chloride will be formed? Let's start with the reaction, so aluminum reacts with chlorine gas. Chlorine is diatomic just like oxygen gas and when combined will form aluminum. chloride now we need to write the formula for aluminum chloride, how can we do it so that aluminum has a positive charge3?

Chloride has a charge minus one, so using the crosslink method it will be al1 cl3 or just Al cl3 now before we start the problem we need. To balance the chemical equation, the number of chlorine atoms is not the same on both sides, but the number of aluminum atoms are the same on both sides, so we have two on the left, three on the right, which I like do is find the minimum. common multiple of two and three or just multiply two and three which is six so to equal them I need six chlorine atoms on both sides so I'm going to put a three in front of cl2 which will give me six and a two in front of al3 so now I have six chlorine atoms but now I have two aluminum atoms on the right side so I have to put two on the left so now we can focus on part A if 35 g of aluminum reacts with the excess chlorine how many grams of aluminum chloride will be formed?

So this is a conversion from grams to G. We need to convert the grams of substance A into G of substance B. Now there are three steps we need to perform to complete this process. First we must change. the units of grams to moles, so we need to convert from GRS of a to moles of substance a and we need to use the molar mass of substance a to do so. Once we have the moles, we need to change from substance A to substance B. then we need to use the relation M for that part finally now that we have the moles, we need to change the unit of moles to G using the molar mass of substance B, so there are three steps we must follow, this is step one. two step three so in our particular example we have the GRS of aluminum and we need to convert it to moles of aluminum now but we need to convert them to aluminum chloride so we have to get the moles of alcl3 and x and finally we can convert them to grams of aluminum chloride so that's an overview of what we need to do in this problem so let's start with what we were given, which is 35 G of aluminum according to a periodic table, the atomic mass of aluminum is 26.98, which means that 1 Mo of aluminum has a mass of 26.98 G.

Next, we must change the substance of aluminum to aluminum chloride so that the M ratio is 2 to 2, so for every two moles of Al that react, 2 moles of aluminum chloride will be produced. Now the last thing we need to do is change the moles of al3 to G, so we need to find the mass M of al3, so we need to add the atomic mass of one aluminum atom with three chlorine atoms, so this is 26.98 + 3 times the atomic mass of chlorine, which is 35.45, so it is equal to 133 33 G per mole so 133 .33 G of al3 is equivalent to 1 Mo of al3 so now let's do the calculations is 35 / 26.98 2 over 2 is 1 so we could cancel both if we want and thenlet's multiply by 133.33 so the final answer is 17296 G of aluminum chloride, so that's the answer for part A, Part B, how many GRS of chlorine will completely react with 42.8 G of aluminum?

So feel free to try that problem, so below we have the grams of aluminum that we need. change it to moles of aluminum and then we'll change a substance using the ratio M to moles of chlorine and then finally diatomic chlorine, so this is cl2, then we'll change it to grams of chlorine, so that's a gr conversion. so let's start with 42.8 g of aluminum and convert it to moles using the same atomic mass which is 26.98 now let's use the M ratio to change it from aluminum to cl2 to make it 2:3 so for every two moles of aluminum that react three moles of chlorine gas react with it, now we need to find the mass M of cl2, it will be 35.45 * 2 which is 70.9, so one mole of cl2 is equal to 70.9 G, so always make sure that the other units will cancel if they don't.

So there's an error somewhere, so now let's finish the problem: It's 42.8/26.98 multiplied by 3/2 and then multiplied by 70.9, so the final answer I have is 168.75. You already know how to perform a mleo mo conversion which we covered in problem one. knowing how to go from moles of one substance to grams of another or grams of one substance to moles of a different substance and you also know how to do a gram to gram conversion, so these are common

stoichiometry

problems

that you can see in a typical chemistry class, so thanks for watching. and have a nice day