Chemistry lab - limiting reagent - Can someone verify?

• John Ker
In summary,The author attempted to solve a problem involving the use of different amounts of hydrochloric acid to produce copper. The calculations showed that using 1M of the acid instead of 7M would still result in the same amount of copper being produced.
John Ker

Homework Statement

Suppose that, for reaction 4, you could not find the bottle of 7 M H2SO4 so you added 5.00 mL of the 1.00 M H2SO4 instead. How would this impact your final yield of Copper. (Show with calculations how this would impact the limiting reagent.)

Homework Equations

CuO(s) + H2SO4(aq) --> CuSO4(aq) + H2O(l)

The Attempt at a Solution

This was the series of transtions done to the copper.
Cu(NO3)2(aq) + 2NaOH(aq) --> Cu(OH)2(s) + 2 NaNO3(aq)

Cu(OH)2(s) + heat --> CuO(s) + H2O(l)

CuO(s) + H2SO4(aq) --> CuSO4(aq) + H2O(l)

CuSO4(aq) + Zn(s)--> ZnSO4(aq) + Cu(s)

I initially started with 10.00ml of .4M Cu(NO3)2. Hence .004 moles. The ratio for each copper reactant to the desired copper product is 1:1. Hence we will end up with .004 CuSO4. Now, in the case of using 7M H2SO4, the CuSO4 is the limiting reagent. However, we use 1M * .005ml = .005mol, doesn't this also keep CuSO4 as the limiting reagent, having no effect on the final yield of copper?

Thanks!

John Ker said:
I initially started with 10.00ml of .4M Cu(NO3)2. Hence .004 moles. The ratio for each copper reactant to the desired copper product is 1:1. Hence we will end up with .004 CuSO4.

We end with Cu, not CuSO4, but yes, 1:1 and 0.004 moles is a constant throughout the process (assuming other reagents are in excess).

Now, in the case of using 7M H2SO4, the CuSO4 is the limiting reagent.

No, it is not, limiting reagent is either CuO or H2SO4. Product is never a limiting reagent.

Somehow your final conclusion (no effect of the final yield) is a correct one.

Borek said:
We end with Cu, not CuSO4, but yes, 1:1 and 0.004 moles is a constant throughout the process (assuming other reagents are in excess).
No, it is not, limiting reagent is either CuO or H2SO4. Product is never a limiting reagent.

Somehow your final conclusion (no effect of the final yield) is a correct one.

Hello, thanks for the response.

So after taking a relook youre right, I overlooked the product being the limiting reagent. In that case, wouldn't CuO be the limiting reagent, since it is only .004moles.
CuO is .004
7M H2SO4 is .035M
1M H2SO4 is .005M

In both cases, even with a reduction in the molarity of H2SO4, CuO is still the limiting reagent, hence the same amount of CuSO4 is produced?

John Ker said:
In both cases, even with a reduction in the molarity of H2SO4, CuO is still the limiting reagent, hence the same amount of CuSO4 is produced?

In general - yes.

Although high concentration of the acid will definitely speed up the reaction, so while theoretically everything is perfectly OK, process can be difficult to do in practice.

1. What is a limiting reagent in a chemistry lab?

A limiting reagent is a reactant in a chemical reaction that is completely consumed, limiting the amount of products that can be formed. It determines the amount of product that can be produced in a reaction.

2. How do you calculate the limiting reagent?

The limiting reagent can be calculated by comparing the moles or mass of each reactant in the reaction and determining which one will run out first. The reactant with the smallest number of moles or mass will be the limiting reagent.

3. Why is it important to identify the limiting reagent in a chemistry lab?

Identifying the limiting reagent is important because it helps to determine the maximum amount of product that can be produced in a reaction. It also allows for the most efficient use of reactants and can prevent wasted resources.

4. How does the limiting reagent affect the yield of a reaction?

The limiting reagent directly affects the yield of a reaction because it determines the maximum amount of product that can be produced. If the limiting reagent is used up, the reaction will stop and the yield will be limited by the amount of that reactant present.

5. Can someone verify the calculation of the limiting reagent?

Yes, someone with knowledge of the reaction and its stoichiometry can verify the calculation of the limiting reagent. It is always a good idea to have a second person check calculations in a chemistry lab to ensure accuracy.

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