Limiting Reaction Question- Getting different answer

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Tara 1F
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Joined: Fri Jun 23, 2017 11:39 am

Limiting Reaction Question- Getting different answer

Postby Tara 1F » Thu Jun 29, 2017 3:09 pm

For this question I'm following the steps from the AV videos but not obtaining the correct answer.
The question is: According to the following equation 0.750g of C6H9Cl3 is mixed with 1.000kg of AgNO3 in a flash of water. A white solid AgCl3 completely precipitates out. What is the mass of AgCL produced?
C6H9Cl3 + 3AgNO3--> AgCl +C6H9(NO3)3
Molar Mass: C6H9Cl3 (187.5 g/mol) , 3AgNO3 (169.88g/mol) and AgCL (143.32g/mol)

Sarah_Wilen
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Re: Limiting Reaction Question- Getting different answer

Postby Sarah_Wilen » Thu Jun 29, 2017 4:36 pm

Hey, friend,

Let's troubleshoot together:
1) Maybe you didn't convert 1.000 kg of AgNO3 to grams and thought that it was the limiting reactant?
2) Chemistry is hard
3) Maybe you got the wrong limiting reactant?
5) Is that the equation given (meaning not balanced yet)? Or is that the equation you balanced. If you balanced that equation already, I see that there is 3 Ag and 3 Cl on the reactant side, but one lonely Ag and Cl on the product side.

Check out my worked out solution. Let me know if you want anything explained!
Attachments
FullSizeRender-3.jpg

Natalie Espadas 1A
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Re: Limiting Reaction Question- Getting different answer

Postby Natalie Espadas 1A » Fri Jun 30, 2017 9:35 am

Hello! After we convert the grams to mols and divide all answers by the smallest answer, do we always have to multiply our numbers by a number to get an answer closest to a whole number? For example:
I have 2.67 mol of Carbon, 2.67 mol of Hydrogen, and 1.97 mol of Oxygen
I multiplied these numbers by 3 in order to get Carbon and Hydrogen closest to 8 and oxygen to 3. Just to clarify, do we always have to do this step?

Daniela_Chem14A
Posts: 27
Joined: Tue Nov 15, 2016 3:00 am

Re: Limiting Reaction Question- Getting different answer

Postby Daniela_Chem14A » Fri Jun 30, 2017 3:12 pm

Yes, you must always multiply in order to get whole numbers as your final answer because there is no such thing as fraction or decimals when writing Compound formulas' subscripts.

Tara 1F
Posts: 21
Joined: Fri Jun 23, 2017 11:39 am

Re: Limiting Reaction Question- Getting different answer

Postby Tara 1F » Mon Jul 03, 2017 4:54 pm

Can you explain how you got the limiting reactant?

I got the second part but still confused on first

Daniela_Chem14A
Posts: 27
Joined: Tue Nov 15, 2016 3:00 am

Re: Limiting Reaction Question- Getting different answer

Postby Daniela_Chem14A » Mon Jul 03, 2017 11:07 pm

You can tell that the limiting reactant is C6H9Cl3 by comparing the solutions. You need 0.012 moles of C6H9Cl3 but, from the chemical reaction, you are only getting 0.004 moles of C6H9Cl3, making it the limiting reactant. On the other hand, AgNO3 is the excess reactant because only 5.89 moles are needed but, through the chemical reaction, you can see that you have 17.66 moles available for use. Hope this helps!
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IMG_3205.JPG

Daniela_Chem14A
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Re: Limiting Reaction Question- Getting different answer

Postby Daniela_Chem14A » Mon Jul 03, 2017 11:27 pm

Sarah,

How did you know to compare C6H9Cl3 to AgCl rather than comparing AgNO3 to AgCl?

Thank you!

Sarah_Wilen
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Re: Limiting Reaction Question- Getting different answer

Postby Sarah_Wilen » Tue Jul 04, 2017 11:20 am

Hey, Daniela,

I compared AgNO3 to C6H9Cl3 because you compare the reactant to the reactant to find the limiting reactant. The mass of the reactants was given, so I compared my calculated mass to the actual mass to tell which reactant was the limiting reactant. You never compare the reactant to the product when finding the limiting reactant. Only reactant to reactant! :)

Hope this helps!

Daniela_Chem14A
Posts: 27
Joined: Tue Nov 15, 2016 3:00 am

Re: Limiting Reaction Question- Getting different answer

Postby Daniela_Chem14A » Tue Jul 04, 2017 1:20 pm

Sarah,

The question asked to find the mass of the product and you used the limiting reactant to do that, C6H9Cl3, how did you know to use C6H9Cl3 instead of AgNO3? I'm referring to the second line of your solution.

Thanks

Sarah_Wilen
Posts: 62
Joined: Fri Jun 23, 2017 11:39 am
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Re: Limiting Reaction Question- Getting different answer

Postby Sarah_Wilen » Tue Jul 04, 2017 2:08 pm

OOHH ok I get what you're asking. I'm too in the 4th of July mood. I used C6H9Cl3 molecule rather than AgNO3 because in order to find the mass of the product, you have to use base the calculations off of the limiting reactant. The limiting reactant dictates when the reaction stops when it is used up. The limiting reactant is the all knowing one. If I used AgNO3, which is in excess, my final mass of the product wouldn't be right because the AgNO3 would react with more C6H9Cl3 than given, hence AgNO3 being the reactant in excess.

The general rule is to base reactions in terms of their limiting reactant.

Hope this helps!


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