Do we have any chemistry gurus here?

Discussion in 'General Science' started by Tekker, Mar 15, 2006.

  1. Tekker

    Thread Starter Active Member

    Apr 22, 2005
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    Hi all,

    I wasn't sure where to post this, but chemistry is pretty much physics, right? :D


    I have a gen chem lab final coming up on Thursday and we are going to be given 10 unlabeled test tubes where we have to identify the substances in each one. So I’m looking for tips, tricks, and basically anything to add that will help this process go as smoothly as possible.

    The substances we are going to be given are:

    Aluminum nitrate - Al(NO3)3
    Ammonia - NH3
    Hydrochloric acid - HCl
    Magnesium nitrate – Mg(NO3)2
    Nitric acid – HNO3
    Silver nitrate – AgNO3
    Sodium carbonate – NaCO3
    Sodium chloride - NaCl
    Sodium hydroxide - NaOH
    Zinc nitrate – Zn(NO3)2

    Our teacher told us that 3 of them are acidic and 3 are basic. However, there’s only two that jump out as being acidic (HCl and HNO3), there’s only one that jumps out as being basic (NaOH). Searching on google for pH levels I found two other possible basic substances (NH3 and NaCO3). The pH levels that I found to be more neutral were NaCl, Al(NO3)3, and Mg(NO3)2. Do these seem right? The two I couldn’t find pH levels for are AgNO3 and Zn(NO3)2, so I have no idea what categories these would fall into.

    We are going to be given time to experiment just before we take the final with each substance labeled so we can see what kind of reactions they undergo and what products are formed. We can also use our lab notebook and any notes we have on the final. So I’m trying to think ahead now and figure out a good plan of action to get through it. Here are the steps I’ve come up with thus far:

    1. Obviously look for any color differences in each substance. I’m assuming they’ll all be clear colored to keep us from getting anything right off the bat, but one can hope. ;)

    2. Test the pH of each substance and set them into groups for acidic, basic, and neutral.

    2.5 See if I can identify any substances right off the bat based on the pH levels. That would be very nice if one or more of them give unique pH levels.

    3. Then I guess it’s just a matter of picking one of the acids and testing that one against all the others to figure out what the acid is. Maybe that’ll help identify others along the way. I don't know which one would be a good one to start with, so I guess just pick any one and go with it?

    The main thing is to make sure that I can narrow it down enough so I don’t end up thinking one substance is something else because they gave a few similar results. Our teacher told us is that HCl + AgNO3 will result in a light purplish color, so if Mg(NO3)2 also gives a purple reaction I need to have some other tests to run so I won’t confuse the two.

    Another thing I’ve looked into is the solubility table to see which ones will form solids and only Na2CO3 and NaOH will form solids. Since they are both bases I’ll have to figure out what else they react with to distinguish them apart.

    That’s pretty much where I’m at for the moment. If anyone has any helpful advice on how to approach this thing, whether it’s adding on to what I have or completely different, I’d really appreciate it. :)

    Thanks
    -tkr
     
  2. n9352527

    AAC Fanatic!

    Oct 14, 2005
    1,198
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    What reagens are available for qualitative analysis?
     
  3. Mazaag

    Senior Member

    Oct 23, 2004
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    I vaguely remember doing something like this in high school ( which was 2 years ago :p) . You might end up using one of the chemicals you identified to help identify others.
     
  4. Tekker

    Thread Starter Active Member

    Apr 22, 2005
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    0

    Unfortunately, none. We only get the 10 chemicals to experiment with. Plus things like pH paper and I imagine all the test tubes we need for mixing the chemicals. Other than that, they haven't told us directly what we will have available.

    <!--QuoteBegin-Mazaag
    @Mar 15 2006, 09:26 AM
    I vaguely remember doing something like this in high school ( which was 2 years ago :p) . You might end up using one of the chemicals you identified to help identify others.
    [post=15030]Quoted post[/post]​
    [/quote]
    That's what I was thinking as well. I'm probably going to have to use at least a couple chemicals to verify others incase several give the same results. I really have no idea what kind of reactions to expect, so I don't know how different they are going to be. I never took chemistry in high school, and I'm finding out that chem lab is definitely not my strong point. :D

    -tkr
     
  5. n9352527

    AAC Fanatic!

    Oct 14, 2005
    1,198
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    I would try to identify the hydrochloric acid and sodium hydroxide first, these, respectively, should be the ones that strongly acidic and basic. Use litmus paper or available pH meter.

    Try to identify the ammonia from the pungent smell. If no smell detected, try adding a few drops of sodium hydroxide to release the ammonium ion from solution.

    Hydrochloric acid is the key to identify the silver nitrate (or any silver ion) where a few drops of silver nitrate into hydrochloric acid solution will form white precipitate.

    Silver nitrate is the key to identify chlorine ion, any white precipitate would indicate this. This test would single out the sodium chloride.

    Use diluted hydrochloric acid to find the only carbonate (sodium carbonate), which would produce carbon dioxide gas (fizzing, colourless gas).

    Now to identify the three nitrate salts and nitric acid. Add ammonium solution to each of them. The one that does not produce any white precipitate is the nitric acid.

    Continue adding ammonium solution, drop by drop, until the white precipitate in one of the solution disappear. This solution, which has soluble white precipitate in excess ammonia, is the zinc nitrate.

    Now add sodium hydroxide to the last two solutions drop by drop until the white precipitate in one of the solution disappear. This solution, which has soluble white precipitate in excess sodium hydroxide, is aluminum nitrate.

    The last solution is magnesium nitrate, which the white precipitate would not dissolve in excess ammonia or sodium hydroxide.
     
  6. Tekker

    Thread Starter Active Member

    Apr 22, 2005
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    0
    Thanks n9352527!

    I actually took the test on Thursday, but that was a lot of great info.

    The way we did the lab was quite a bit different than what I was expecting.... I'm on my way out the door right now, but I can explain more about what we did when I get back.


    BTW, I got 100% on it! Woot!!! :D

    -tkr
     
  7. rrowdy33

    New Member

    Mar 10, 2009
    1
    0
    I have the same test chemistry lab test tomorrow... It would be a huge help to have some advice! Please let me know soon if possible.
    Thanks-
    k
     
  8. studiot

    AAC Fanatic!

    Nov 9, 2007
    5,005
    513
    I can't imagine you would be given a test tube of ammonia as it is a gas.

    If the stuff is a colourless liquid it will be ammonium hydroxide.
    If it is a white powder it will be ammonium carbonate.

    You have enough reagents in the 10 tubes plus the list to identify the stuff.

    Look up the solubility of carbonates, chlorides etc and their colours. Then try to work out what will happen if you mix some of the chemicals you are given. Leave some to mix with other things.

    Just realised how old this thread is.
     
    Last edited: Mar 10, 2009
  9. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    5,440
    811
    It is an old post, but something to think about. The hardest distinction might be aluminum nitrate from magnesium nitrate. The rest are pretty straight forward. Aluminum is amphoteric, and its nitrate should be soluble in both acid and strong base (NaOH). Magnesium is not amphoteric, and its nitrate with NaOH should precipitate Mg(OH)2, which has a solubility of only 1.2 mg/ 100mL water (Source: Wikipedia)

    John
     
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