vaguest question ever

[run-bandit]

So it did this chemistry gravimetric analysis in high school chemistry...

I did all the calculations and came up to question saying: if another ion were present in the sample of rock phosphate that formed a precipitate with oxalate ions, how would this affect the calculated rest of the amount of moles of Ca in the precipitate an the percentage by mass of calcium in the phosphate rock.

It was a standard textbook gravimetric analysis question so I won't even say it (unless a few of you tell me i haven't given enough info).

When I asked my teacher he said: "It varies it might increase it or decrease it"

[Martoman]

It will increase. If another precipitate is formed with the precipitate of Ca WHICH YOU WANT then the mass of the WHOLE precipitate which you will get at the end of the process will increase.

Usually, in an ideal world we have:
mass of precipitate (containing ion we want to isolate) contains all of those ions.

However sometimes there are other ions which will precipitate. Then the resultant precipitate would be:

Other precipitate + precipitate we want = HIGHER than the expected mass value. Since there is no easy way to determine the precipitates apart (unless they are distinctly different) you assume all the precipitate is this. Given this assumption, the result will obviously be higher.

[superflya]

if u have another unwanted ion precipitate forming, thinking logically.. it would increase the mass of the whole precipitate.

[herzy]

teacher is wrong, + 3 more precipitate always = greater than expected result