Finding limited reactant (Chem 101)

  • Thread starter legendarium
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In summary, the conversation discusses finding the limited reactant in a double replacement reaction involving Silver Nitrate and Potassium Chromate. The participants go through the steps of balancing the chemical equation and calculating the molar masses of the reactants and products. They also discuss the concept of limiting reagents and how to determine which reactant is the limiting one. The conversation ends with the participants concluding that the given information is enough to solve the problem and finding the mass of the products formed.
  • #1
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.
 
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  • #2
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

[tex]C = \frac n V[/tex]

Solve for n.
 
  • #3
Yes i figured that out last night...

So, is this right?
 
  • #4
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.
 
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  • #5
im assuming my original post is not clear.

i think i did exactly that.

Thank you.
 
  • #6
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.
 
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  • #7
It did, thank you.
 

FAQ: Finding limited reactant (Chem 101)

1. What is a limited reactant?

A limited reactant is a substance that is completely used up in a chemical reaction, causing the reaction to stop. It determines the amount of product that can be formed in the reaction.

2. How do you determine the limited reactant in a chemical reaction?

To determine the limited reactant, you must first write out the balanced chemical equation for the reaction. Then, calculate the moles of each reactant present. The reactant with the smaller number of moles is the limited reactant.

3. What happens if you have an excess of one reactant in a reaction?

If you have an excess of one reactant, it means that there is more of that reactant present than is needed for the reaction to occur. This excess reactant will not be used up and will remain in the mixture after the reaction is complete.

4. Can the limited reactant change in different trials of the same reaction?

Yes, the limited reactant can change in different trials of the same reaction. This can happen if the initial amounts of the reactants are different in each trial. It is important to calculate the moles of each reactant for each trial to determine the limited reactant.

5. How does the limited reactant affect the amount of product formed?

The limited reactant determines the maximum amount of product that can be formed in a reaction. Once the limited reactant is completely used up, the reaction stops and no more product can be formed. The amount of product formed will be determined by the amount of the limited reactant present.

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