Sapling Homework 1 Q#9
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Sapling Homework 1 Q#9
Under the hint tab, we are told to calculate the amount of grams of hydrogen and carbon in the products as a step towards the solution. How do I go about finding the amount of grams for both? Must I calculate the molar mass of each product and go from there?

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Re: Sapling Homework 1 Q#9
Yup! You do have to calculate the molar mass for each because you want to convert the given masses into mols for the molecules and then use stoichiometry to find the mols of C and H used in the reaction.
So basically, you're finding the mols of C and H the reaction uses from the given masses of CO2 and H20.
So basically, you're finding the mols of C and H the reaction uses from the given masses of CO2 and H20.

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Re: Sapling Homework 1 Q#9
Yes, because of the law of conservation of mass, the same mass of C and H are in the products (CO2 and H2O) as there is in caproic acid. After finding the mass of C and H, you could subtract from 1.000g to get the mass of O. From there, you can do the basic calculation to find the empirical and molecular formula.

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Re: Sapling Homework 1 Q#9
Yes, you will calculate the molar mass of the product and then from there, what I did was set up a proportion:
(atomic mass of carbon)/(molar mass of product) = (the mass of carbon in the product which is the unknown "x")/(sample mass of product given)
That should give you the mass of carbon produced and therefore the mass initially started with in the reactant. Do the same with hydrogen. Hope that helps!
(atomic mass of carbon)/(molar mass of product) = (the mass of carbon in the product which is the unknown "x")/(sample mass of product given)
That should give you the mass of carbon produced and therefore the mass initially started with in the reactant. Do the same with hydrogen. Hope that helps!

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Re: Sapling Homework 1 Q#9
Here's what I did, if there is a quicker way, please let me know :)
1) calculate molar mass of each known compound
2) calculated the amount of grams for C and H elements (element mass/total mass of compound)
3) after knowing the weight of C and H elements, subtract them from 1.000 g (given) to find O weight
4) convert grams to moles for each element
5) divided the moles by the moles of the smallest element to find ration
6) test to see if molar mass of the formula adds up to the given Molar mass (110g +10)
7) if no, that is the empirical formula, if yes, molecular formula
1) calculate molar mass of each known compound
2) calculated the amount of grams for C and H elements (element mass/total mass of compound)
3) after knowing the weight of C and H elements, subtract them from 1.000 g (given) to find O weight
4) convert grams to moles for each element
5) divided the moles by the moles of the smallest element to find ration
6) test to see if molar mass of the formula adds up to the given Molar mass (110g +10)
7) if no, that is the empirical formula, if yes, molecular formula

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Re: Sapling Homework 1 Q#9
The way I approached the problem so that it made sense for me was to first find the mass percentage of C in CO2, using molar mass, and use that percent (27.30%) on the amount of CO2 produced (2.275g) to find out how many grams of carbon were produced in the reaction (0.620g). You do the same procedure for the hydrogen in H2O. And, because of the law of the conservation of mass, the same amount of carbon and hydrogen produced must have been present in the caproic acid (reactant). Because you know that 1.000 grams of caproic acid was reacted in excess oxygen, you can subtract the amount of C and H present to find out how many grams of O there are. Using these values, you can find the empirical formula.

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Re: Sapling Homework 1 Q#9
I got stuck in the beginning too because I was trying to find the amount of O2 that was consumed. I added the mass of the products and subtracted 1g (the amount of caproid acid consumed), but was this step not necessary information to find? I figured then you could determine the difference in O2 on both sides of the reaction to know how much O2 was in caproic acid, and then you do the same with the masses of C and H. Not sure if that makes sense, but could you do it that way? I found the answer using the steps people previously suggested, but I'm just curious.

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Re: Sapling Homework 1 Q#9
Start by covering the grams to moles, and then take the element mass/ molar mass of the compound to find the molar ratio.

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Re: Sapling Homework 1 Q#9
Yeah you would convert the grams of CO2 and and H2O to moles of C and H, respectively. The problem is asking for moles of C and H, so you would just convert the grams CO2 and H2O to moles of CO2 and H2O to moles of C and H and then finally to grams of C and H.

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Re: Sapling Homework 1 Q#9
So this is how I solved the problem:
1. To find the grams for C, you have to use the molar mass of C (12.01 g/mol) and the mass of the compound CO2 (44.01 g). You would divide the molar mass of C by the compound mass (C/CO2). This gives you the grams for C.
2. To find the grams for H, you would do the same thing as you did in the first step. First, you would divide the molar mass of H (2.016) by the compound mass H2O (18.02). It would look like this (H/H20).
3. You would then subtract to find the grams for O. It would look like this ( Oxygen = 1.000 g  (Carbon grams + Hydrogen grams)). You would just need to input what you got from step 1 and 2 into that.
4. Now that you have C, H, and O in grams, you can now convert them individually into moles (g divided by g/mol).
5. Once you have them all in moles, you would use the smallest value and divide the moles to find the ratio. With the ratio, you can find the empirical formula.
6. To find the molecular formuala, you need to find the molar mass of the empirical formula. Once you have it, you divide the value given in the beginning (110 g) by the molar mass. Round the value if needed and multiply it with the empirical formula. This will give you the molecular formula
1. To find the grams for C, you have to use the molar mass of C (12.01 g/mol) and the mass of the compound CO2 (44.01 g). You would divide the molar mass of C by the compound mass (C/CO2). This gives you the grams for C.
2. To find the grams for H, you would do the same thing as you did in the first step. First, you would divide the molar mass of H (2.016) by the compound mass H2O (18.02). It would look like this (H/H20).
3. You would then subtract to find the grams for O. It would look like this ( Oxygen = 1.000 g  (Carbon grams + Hydrogen grams)). You would just need to input what you got from step 1 and 2 into that.
4. Now that you have C, H, and O in grams, you can now convert them individually into moles (g divided by g/mol).
5. Once you have them all in moles, you would use the smallest value and divide the moles to find the ratio. With the ratio, you can find the empirical formula.
6. To find the molecular formuala, you need to find the molar mass of the empirical formula. Once you have it, you divide the value given in the beginning (110 g) by the molar mass. Round the value if needed and multiply it with the empirical formula. This will give you the molecular formula

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Re: Sapling Homework 1 Q#9
Absolutely! That is the first step in solving the problem. Using the given molecular weight of CO2, you can find the amount of carbon present in the product (it is the only substance with carbon). You can start by converting it to moles of CO2 instead, and then use that to find how many moles of carbon are in that specific amount of moles of CO2. If you are stuck on this step, ask yourself, how many moles of carbon are in CO2? (Hint: It's one!) You do this as well with H2O, only in this case you are solving for the amount of moles of hydrogen present in the moles of H2O present in the products. Now that you have found the moles of carbon and hydrogen in the products, oxygen is virtually isolated as the last remaining element in the products that is unaccounted for. Begin by taking the number of moles of carbon and hydrogen and converting them to grams (you will see why we do this in just a second) using their known molar mass. The problem should have provided you with information about the initial molecular weight of the caproic acid sample, which we can subtract by the sum of the molecular weights of carbon and hydrogen we just found to find the amount of oxygen present in grams. Afterwards, we convert that to moles of oxygen. Why? So for all the elements present in the products (C, H, O), we know the number of moles of each one. Like Professor Lavelle showed in his example, we proceed here by dividing by the smallest amount of moles to find the individual amount of each atom present in the resulting formula. Remember, we do not know if this formula is empirical or molecular, so we must find the molar mass of it and check it against what was given to differentiate which one it is. If it is exactly the same, congratulations, you have found the molecular formula, which can be used to find the empirical formula by dividing by a common factor that gives you a substance whose number of individual atoms can no longer be reduced. If it is not the same, then you have found the empirical formula. To find the molecular formula, divide the given molar mass by the one you found to find the difference between the two formulas. Then, multiply the empirical formula by that difference. Sorry for the long answer, but hope this helps!

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Re: Sapling Homework 1 Q#9
Aimee Alvarado 2K wrote:So this is how I solved the problem:
Thank you so much for listing it out stepbystep. I was really struggling and the detailed instructions helped.

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Re: Sapling Homework 1 Q#9
Hi, I took the given grams of CO2 and H2O and divided by their molar masses to find them in mols. Then I multiplied them with the ratios, for example in CO2, there is 1 C per CO2 and 2 O in CO2. So the mols times 1C/1CO2 to fin the mols of C alone. Then multiplied it with 12 to find grams of carbon. I did the same to find grams of hydrogen in H2O. Then I added the grams of hydrogen and carbon and subtracted that from 1g of CHO (given) to find the grams left over for oxygen. Then I took the grams of oxygen and divided by 16 to get mols of oxygen. I did the same for hydrogen and carbon to find them in mols. Then divided by the smallest number to find empirical formula. Then I used the given molar mass and divided by the calculated molar mass of the empirical formula to find how much I should multiple to get the molecular formula.

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Re: Sapling Homework 1 Q#9
I was super confused on this problem too. It took me awhile to get it. Thank you for everyone who explained it step by step, that really helped.

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Re: Sapling Homework 1 Q#9
This question also confused me initially, but I decided to first convert the grams of CO2 and grams of H2O into moles because I knew that is usually one of the steps in solving for the empirical formula. After doing so I realized that it was critical to the problem that we know what mass of oxygen was in the original sample. Once I had this mass of oxygen converted into oxygen moles, I was able to find the empirical formula.

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Re: Sapling Homework 1 Q#9
Yes. You calculate the molar mass of each product and then you use that to calculate the number of moles of each product.

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Re: Sapling Homework 1 Q#9
Yeah! Use the molar mass and convert it to grams of each using dimensional analysis and just subtract the sum of both from the total. Hope this helps!

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Re: Sapling Homework 1 Q#9
In the step by step answers listed, no one lists the step of multiplying each element by the smallest number to get an integer after dividing the mols by the smallest number of the three elements. I thought this was an essential step to do from the audio visual focus topics and lecture. Is everyone just rounding the numbers they get after dividing by the smallest number to get to a whole number or are they still multiplying each element by the smallest number to get a nondecimal number?

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Re: Sapling Homework 1 Q#9
Daniela Santana 3D wrote:In the step by step answers listed, no one lists the step of multiplying each element by the smallest number to get an integer after dividing the mols by the smallest number of the three elements. I thought this was an essential step to do from the audio visual focus topics and lecture. Is everyone just rounding the numbers they get after dividing by the smallest number to get to a whole number or are they still multiplying each element by the smallest number to get a nondecimal number?
I was also wondering this, as I have always been taught to make my answers more accurate by including more decimals. When I checked my work with another student to try and solve this problem her answer was not the same as mine due to simplifying.

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Re: Sapling Homework 1 Q#9
I also had trouble determining how to approach this question, but this thread was very helpful. I think it was really key to understand how to use the grams of products given to find the mass and moles of C, H, and O. From there, the rest of the problem was generally straight forward!

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Re: Sapling Homework 1 Q#9
Tobie Jessup Section 3D wrote:I also had trouble determining how to approach this question, but this thread was very helpful. I think it was really key to understand how to use the grams of products given to find the mass and moles of C, H, and O. From there, the rest of the problem was generally straight forward!
I actually have to disagree with this. Once I found the mass and moles of C, H, & O I was a bit confused on how to use those numbers to find the empirical formula but after some time I was able to figure it out. I may go to a step up session to get complete clarification though.

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Re: Sapling Homework 1 Q#9
I was stuck on this problem too but this thread helped so much so thank you all !
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