[LimitingRX]

I have not, without certainty, been able to figure out the following question:

Why must the precipitate in a solution be allowed to settle before collecting the supernatant to determine the limiting reactant in the original salt mixture?

My "answer": Because the reaction might not have fully completed, and when the supernatant is tested to determine the limiting reactant by adding drops of test reagents, both test reagents will form a precipitate.

Is that correct? I've done a lot of research online, and the only thing I am finding is that the precipitate must be allowed to settle - without given an explanation of why.

Thanks

[Borek]

What does it mean "to settle" - where is the precipitate before it settles?

[LimitingRX]

We start with a salt mixture. Water is then added to this salt mixture, and it is heated to digest the precipitate. We are supposed to let this solution cool for a couple of mines to allow the precipitate to settle. After the precipitate has settled, we withdraw 2 volumes of the supernatant to be used to determine the limiting reactant in the original salt mixture.

If we rushed the experiment and did not allowed the solution to cool and precipitate to settle before we collected the supernatant (which now has some precipitate in it), how would that affect our tests in determining the limiting reactant in the original salt mixture?

We add drops of test reagents to the 2 different volumes collected of the supernatant to determine the limiting reactant.

Thanks

[LimitingRX]

We start with a salt mixture. Water is then added to this salt mixture, and it is heated to digest the precipitate. We are supposed to let this solution cool for a couple of mines to allow the precipitate to settle. After the precipitate has settled, we withdraw 2 volumes of the supernatant to be used to determine the limiting reactant in the original salt mixture.

If we rushed the experiment and did not allowed the solution to cool and precipitate to settle before we collected the supernatant (which now has some precipitate in it), how would that affect our tests in determining the limiting reactant in the original salt mixture?

We add drops of test reagents to the 2 different volumes collected of the supernatant to determine the limiting reactant.

Thanks

cool for a couple of minutes*

I just realized I didn't answer your question, Borek. The salt mixture and water are on a beaker that will be heated to digest the precipitate.

[LimitingRX]

After further research, I found this:

If the supernatant is not clear, complete precipitation has not occurred. When I test the 2 supernatant volumes to determine the limiting reactant, a precipitate will form with both test reagents. I will be unable to determine the limiting reactant this way.

Is that correct?

Thanks

[Borek]

If the supernatant is not clear, complete precipitation has not occurred.

Do you understand now what I asked and why?