March 28, 2024, 08:48:24 AM
Forum Rules: Read This Before Posting


Topic: I'm slightly confused about a lab i did.  (Read 1832 times)

0 Members and 1 Guest are viewing this topic.

Offline dume85

  • Very New Member
  • *
  • Posts: 1
  • Mole Snacks: +0/-0
I'm slightly confused about a lab i did.
« on: April 06, 2018, 03:48:07 PM »
I have a lab report i'm working on.
these are not "lab questions" im just trying to remove sources of error that are only 0.00001% from my lab report conclusion. I may just be way over thinking it too.

25ml of 0.002M Fe(NO3)3(aq) 5ml-25ml of 0.002M KSCN(aq) and 20ml-0ml of  extra 0.1M HNO3 were used. the aq solutions solvent was HNO3 i just realized that it everything make so much more sense now. I thought it was water before.

resulting Kc. KSCN is increasing by 5 ml for each run starting at 5ml.
1. Kc=293
2. Kc=308
3. Kc=353
4. Kc=343
5. Kc=356

I'm pretty sure temperature didn't cause the difference in Kc, unless a very small change in temperature could do it, but i don't know how to prove it.
So in the reaction of SCN-1 + Fe3+3 <--> FeSCN+2  is there a way to find how much ΔT would be needed to change the Kc by about 50?

What I have so far
A colorimeter was used to determine concentrations of FeSCN+2 at eq(it's a dark red color). We used HNO3 as a blank but I heard the ideal blank is one that would have all the reactants and none of the products that way you are accounting for all the light already being absorbed by the reactants. We also used Fe(NO3)3(aq) which was already a yellow or orange color, so at the very least that should have been used as the blank right?

fingerprints were likely on some of the cuvettes so that should cause some readings if not all of them to be off. If fingerprints were on the blank all reading should be wrong.

All calculations were done assuming nothing else would react with the SCN-1, Fe3+3, and FeSCN+2. This seems approximately correct unless the NO3-1 ions from Fe(NO3)3 started bonding with FeSCN+2. I would assume this wouldn't happen as the HNO3 solvent is already causing NO3-1 to separate from its original cation pair. There was also a small volume of air trapped in our capped off flasks and cuvettes so maybe that found some way to interact with it but that should only cause a negligible amount of error.

Offline Arkcon

  • Retired Staff
  • Sr. Member
  • *
  • Posts: 7367
  • Mole Snacks: +533/-147
Re: I'm slightly confused about a lab i did.
« Reply #1 on: April 19, 2018, 02:37:36 PM »
To tell the truth, its hard to follow your posting.  I don't actually see a question anywhere.  Certainly, you can rewrite it -- the protocol you followed can go in an outline to start with.  After all, the lab was written already, people know what was done.  After your results, you can discuss sources of errors, again, as an outline.

We have a rule, on these forums, against "word soup".  Your I did this, and then I..., and then I, So these numbers, oh, by the way, I forgot to mention previously I ...

That makes for a convoluted novel, science isn't done that way.
Hey, I'm not judging.  I just like to shoot straight.  I'm a man of science.

Sponsored Links