August 17, 2019, 07:01:07 AM
Forum Rules: Read This Before Posting


Topic: Qualitative Analysis Lab: Possible Sources of Error  (Read 27852 times)

0 Members and 1 Guest are viewing this topic.

Offline shell

  • Very New Member
  • *
  • Posts: 2
  • Mole Snacks: +0/-0
Qualitative Analysis Lab: Possible Sources of Error
« on: November 23, 2009, 06:21:56 PM »
Basically what we had to do in this lab was add these solutions:
NaCl
Na2SO4
NaOH
to an unknown solution suspected of containing silver, barium and iron ions. The solutions were added in the order I listed to see if a precipitate formed. They were added in this way so there would be no conflict with the the NaOH which reacts with everything. Everytime a solution was added, if a precipitate formed, it was filtered out and the next solution was added. A precipitate did form each time a solution was added.

My question is: What are some possible sources of error when doing this experiment? I have searched up some possibilities but all I get is glassware contamination and human error, which our teacher told us stay away from. I'm thinking that some of the precipitate may not have been filtered out, causing it to react with the NaOH giving false results. The solutions may also not have been concentrated enough so the precipitate didn't appear. I would like some more suggestions for possible errors, and confirmation on whether or not my ideas are correct.

Also, what colour should the precipitates be when the solutions were added? When I added NaCl it was yellow (silver ions), for Na2SO4 it was pale yellow (barium), and for NaOH it was brown (iron? this is the one that I am most unsure of.)

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 25123
  • Mole Snacks: +1650/-396
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: Qualitative Analysis Lab: Possible Sources of Error
« Reply #1 on: November 24, 2009, 02:48:06 AM »
Brown for iron is OK.

What if you have added too small amount of a reagent to precipitate one of the ions?
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

Offline shell

  • Very New Member
  • *
  • Posts: 2
  • Mole Snacks: +0/-0
Re: Qualitative Analysis Lab: Possible Sources of Error
« Reply #2 on: November 24, 2009, 04:06:13 PM »
That sounds good, but I'm not sure how I would be able to fix that error. Also, were the possible errors I listed plausible?

If there are any errors that probably can't be corrected in a classroom (ie. need for better equipment, or other random errors), I need help thinking of some.

If there is a site that lists these types of errors, could a link be provided? Thanks.

Sponsored Links