Finding limited reactant (Chem 101)

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Discussion Overview

The discussion revolves around identifying the limiting reactant in a double replacement reaction involving Silver Nitrate and Potassium Chromate, with a focus on using molarity and volume rather than mass. Participants explore the necessary calculations and concepts related to stoichiometry in a chemistry homework context.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation

Main Points Raised

  • One participant expresses uncertainty about how to start the problem using molarity and volume, suggesting that they could solve it if given the grams of each molecule.
  • Another participant emphasizes the importance of using moles instead of mass, referencing the relationship between concentration, moles, and volume.
  • A later reply clarifies that the calculation should focus on the moles of reactants rather than products, correcting the initial approach regarding the involvement of KNO3.
  • One participant acknowledges confusion about their original post and seeks confirmation on their understanding of the problem.
  • Another participant provides a corrected calculation for determining the mass of the product formed from the reactants, indicating how to find the limiting reagent based on the amounts of each reactant.

Areas of Agreement / Disagreement

There is no consensus on the correct approach initially, as participants express differing views on whether to calculate using mass or moles. However, some participants agree on the necessity of focusing on moles for the calculations.

Contextual Notes

Participants demonstrate varying levels of understanding regarding stoichiometric calculations, with some confusion about the roles of different reactants and products in the reaction.

Who May Find This Useful

Students studying introductory chemistry, particularly those learning about stoichiometry and limiting reactants in chemical reactions.

legendarium
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Homework Statement



Find the limited reactant: Silver Nitrate and Potassium Chromate mix in a double replacement.

Silver Nitrate: 2.15 mL, 0.153 M ; Potassium Chromate: 1.08 mL, 0.197 M.

The Attempt at a Solution



I balanced and have a chemical reaction of:
2AgNO3 + K2Cro4 -> Ag2Cro4 + 2KNO3

I can solve this problem if i was given the grams of each molecule. But I am not sure how to start the problem with Molarity and Volume.

I think i would need to do this:

0.153 mol AgNO3 /1L (0.00215L AgN03) (2mol KNO3/2mol AgNo3) (101.1 g KNO3/1mol KNO3) = 0.033gAgNo3

So, how does this look? This is only one of the two equations but i can figure the other one out if if this is right.
 
Last edited:
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legendarium said:
I can solve this problem if i was given the grams of each molecule.

Do you know how to read chemical reaction equation? It is given in terms of moles, so while it can be easily converted to masses, there is no need for that.

By definition

C = \frac n V

Solve for n.
 
Yes i figured that out last night...

So, is this right?
 
As I told you - don't calculate mass of the reactant, calculate number of moles.

And I have no idea what you did - KNO3 doesn't play any role here and is not involved.
 
Last edited by a moderator:
im assuming my original post is not clear.

i think i did exactly that.

Thank you.
 
legendarium said:
I can solve this problem if i was given the grams of each molecule. But I am not sure how to start the problem with Molarity and Volume.

What you need to find is the mass of the products formed using the amounts of each reactant present at the beginning of the rxn.

0.153 mol AgNO3 /1L (0.00215L AgN03) (2mol KNO3/2mol AgNo3) (101.1 g KNO3/1mol KNO3) = 0.033gAgNo3

The concept is correct but you are mixing up the reactants and the products.

Technically it would be: (using AgNO3 as the reactant to find product)

(0.00215 L AgNO3 * 0.153 mol/L AgNO3)*(1 mol Ag2CrO4 / 2 mol AgNO3)*(331.73g / 1 mol Ag2CrO4) = 0.0546 g Ag2CrO4

You can figure out the grams of Ag2CrO4 produced using the amount of the potassium chromate given. That should tell you which is the limiting reagent.

Hope this helps.
 
Last edited:
It did, thank you.
 

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