Mass Relationships In Chemical Reactions

[DarylMBCP]

Homework Statement

Styrene is a Hydrocarbon. If 0.438g of Styrene is burned in Oxygen and produces 1.481g of CO2 and 0.303g of H20, what is the empirical formula of styrene?

Homework Equations

The Attempt at a Solution

No. of moles of CO₂ - 1.481g / 44.0107g/mol = 0.0337mol
No. of moles of C - 0.0337mol
No. of moles of H₂O - 0.303g / 18.016g/mol = 0.0168mol
No. of moles of H - 2 x 0.0168mol = 0.0336mol
Mole ratio of C and H - 0.0337 : 0.0336
1 : 1

Is this ratio the empirical formula of Styrene?

 

[Emily266]

I got the same answer when I tried it.

 

[DarylMBCP]

Thank you for confirming my answer. By the way, does the coefficient of each compound in a balanced equation affect the number of moles of that substance?
Example:
There is an equation where there is H₂O and the question says that the number of moles of H₂O is 4 moles. If I balance the equation and the coeffcient of H₂O happens to be 2, does that mean that the no. of moles of becomes 8 moles?

Thanks for answering my first question again.

 

[Emily266]

You're welcome!

To answer your second question- the moles of H2O could be affected, but it would depend on what the question is asking you to do. If you post the entire question, I might be of more assistance.

 

[DarylMBCP]

Thanks for responding but I managed to solve that problem myself but faced a new one. Please help me for this one too. Thanks a lot.

Element Z reacts with Hydrogen to produce a pure sample of Z₂H₅ in an experiment, it is found that 1.0g of Z produces 2.7896g of Z₂H₅ . How do I find the molar mass of Z?

Is this possible?
2.7896 - 1 = 1.7896 (Mass of Oxygen)
1.7896g / 3 x 1.008g/mol = 0.5918mol (Of O₃)
Mole ratio of Z₂H₅ - 2:5
0.5918 / 5 x 2 = 0.23672mol (No. of moles of X)
1g / 0.23672mol = 4.22441g/mol.

Is it correct to take the mass of Oxygen present / The molar mass of O₃ to get the number of moles of O₃? If so, is it correct to take the number of moles of O₅ / 5 x 2 or take the number of moles of O / 5 x 2?

Thanks again for helping!

 

[Emily266]

I was looking at a problem like this in another thread. I am only in my first quarter of AP Chem and we have not worked with problems like this yet. Here is the thread https://www.physicsforums.com/showthread.php?t=261923". These problems have me fired up now! I'm going to class early today so I can have my teacher show me how to do them! :]
I'm sorry I could not be of greater assistance.

 

[DarylMBCP]

Kk, pls show me the solution when you are done. Thank you.

 

[Emily266]

Thanks for responding but I managed to solve that problem myself but faced a new one. Please help me for this one too. Thanks a lot.

Element Z reacts with Hydrogen to produce a pure sample of Z₂H₅ in an experiment, it is found that 1.0g of Z produces 2.7896g of Z₂H₅ . How do I find the molar mass of Z?

Is this possible?
2.7896 - 1 = 1.7896 (Mass of Oxygen)
1.7896g / 3 x 1.008g/mol = 0.5918mol (Of O₃)
Mole ratio of Z₂H₅ - 2:5
0.5918 / 5 x 2 = 0.23672mol (No. of moles of X)
1g / 0.23672mol = 4.22441g/mol.

Is it correct to take the mass of Oxygen present / The molar mass of O₃ to get the number of moles of O₃? If so, is it correct to take the number of moles of O₅ / 5 x 2 or take the number of moles of O / 5 x 2?

Thanks again for helping!

In the first part of your problem you say that you are looking for Z₂H₅, but then in your work you are using O. I am not quite sure where you are getting that from.

My chem teacher briefly showed me how to do it and did not have time to check my answer. I am 99% positive that I got the wrong answer though. It came out to be some thing like 2x+50395g/1383867447moles lol. I will ask her about it again tomorrow. I am sorry if this is due before then.

 

[Borek]

Thank you for confirming my answer. By the way, does the coefficient of each compound in a balanced equation affect the number of moles of that substance?

Learn how to read chemical reactions - I think it should answer your question.

 

[Borek]

Element Z reacts with Hydrogen to produce a pure sample of Z₂H₅ in an experiment, it is found that 1.0g of Z produces 2.7896g of Z₂H₅ . How do I find the molar mass of Z?

Is this possible?
2.7896 - 1 = 1.7896 (Mass of Oxygen)
1.7896g / 3 x 1.008g/mol = 0.5918mol (Of O₃)
Mole ratio of Z₂H₅ - 2:5
0.5918 / 5 x 2 = 0.23672mol (No. of moles of X)
1g / 0.23672mol = 4.22441g/mol.

Is it correct to take the mass of Oxygen present / The molar mass of O₃ to get the number of moles of O₃? If so, is it correct to take the number of moles of O₅ / 5 x 2 or take the number of moles of O / 5 x 2?

Your post is so inconsistent because of this hydrogen/oxygen thing that it is hard to help. You are partially wrong and partially OK.

 

[DarylMBCP]

I think I kinda got mixed up with Oxygen and Hydrogen. This is what I meant;

Element Z reacts with Hydrogen to produce a pure sample of Z₂H₅ in an experiment, it is found that 1.0g of Z produces 2.7896g of Z₂H₅. How do I find the molar mass of Z?

Is this possible?
2.7896 - 1 = 1.7896 (Mass of Hydrogen)
1.7896g / 5 x 1.008g/mol = 0.3551mol (Of H)
Mole ratio of Z2H5 - 2:5
0.3551 x (2/5) = 0.14204mol (No. of moles of X)
1g / 0.14204mol = 7.0403g/mol.

Is it correct to take the mass of Hydrogen present divided by the molar mass of H₅, to get the number of moles of H₅? If so, is it correct to take the number of moles of H₅ x (2/5) or take the number of moles of H x (2/5)?

Thanks for helping again!

 

[Borek]

2.7896 - 1 = 1.7896 (Mass of Hydrogen)

OK

1.7896g / 5 x 1.008g/mol = 0.3551mol (Of H)

No. 1.7869/1.008 = 1.773 mol of H. What you calculated would be 0.3551 mol of H₅, whatever it means. Not much.

Mole ratio of Z2H5 - 2:5

OK

0.3551 x (2/5) = 0.14204mol (No. of moles of X)

OK, although numbers are incorrect because you were wrong earlier.

1g / 0.14204mol = 7.0403g/mol.

OK, although numbers are incorrect because you were wrong earlier.

Is it correct to take the mass of Hydrogen present divided by the molar mass of H₅, to get the number of moles of H₅? If so, is it correct to take the number of moles of H₅ x (2/5) or take the number of moles of H x (2/5)?

As long as you are consistent you can calculate it whichever way want. But you can't go for number of moles of H₅ and then multiply it by 2/5 - you have to multiply it by 2. At the same time if you have number of moles of H you have to multiply it by 2/5, but you can't by 2.

My advice: forget about the H₅ approach. It gives correct results when done properly, but you may have a hard time trying to convince your teachers that you were on the right track.

 

[DarylMBCP]

As long as you are consistent you can calculate it whichever way want. But you can't go for number of moles of H₅ and then multiply it by 2/5 - you have to multiply it by 2. At the same time if you have number of moles of H you have to multiply it by 2/5, but you can't by 2.

Is it true to say that if I take the mass of an element, X₅ for example, and divide it by the molar mass of X times the subscript(5), I will get the number of moles of X5?

 

[Borek]

Is it true to say that if I take the mass of an element, X₅ for example, and divide it by the molar mass of X times the subscript(5), I will get the number of moles of X5?

Yes. That's what is routinely done for diatomics, like O₂.

Just try to be precise, when you write

mass of an element, X₅ for example

it raises a brow - no such element as X₅. X₅ is a molecule. Element is X.

 

[DarylMBCP]

Thanks very much. I've finally got it.