[sammysue07]

I posted this question ealier today, but i cant seem to find it and add to it....

here is my problem, it is for a Science Olympiad competition this coming saturday, and i just got information for this competition today.

we will have ten solids: sodium bicarbonate, sodium sulfite, magnesium hydroxide, calcium carbonate, sodium dihydrogen phosphate, ammonium chloride, zinc chloride, potassium iodide, potassium hydroxide, and aluminum nitrate.

we will be able to choose one of the four chemical solutions to use in identifying the substances: 3M HCl, 3M NaOH, Phenolphthalein indicator solution, or 0.1M AgNO3.

my question i guess is what solution would be the best in determining what the substances are? and should we look at any other characteristics besides what happens with the solution in determining what it is??

i have looked all over the internet, and i am finding really nothing.  i havent had a chance to look at any books, but my teacher/coach does have many different chemistry books....

what do you suggest?

Thanks for all of your help.
samantha

[Donaldson Tan]

the line of thought (in my opinion) is which test chemical can identify one of the unknown solutions in one test, then i can use both chemicals (the one i just identified and the test reagent) to identify the rest of the unknown solutions.

[sammysue07]

wow.. i am really confused.  i get that you can test with one reagent to find out substance 1, and then use that to find out the other, but which one would you suggest.

we also will have access to distilled or deionized water... with that information, can youi give me any more help??

thank you very much
samantha

[savoy7]

Sammysue07,

there are a couple of ways one would go about doing this.  Geodome is right on with his reasoning.  Since this is for a science olympiad contest and you haven't posted any work I will say this:

1)you have access to dH₂O

2)maybe this attachment might get you thinking

Post your thoughts and maybe someone will reply with some more help,
savoy 7

[savoy7]

I'll try to attach the file again

[sammysue07]

hm... i will check out the attachment....

i printed it and wil read it soon

[Garneck]

If you have access to water and you can dissolve those compunds, then:
1. Mg(OH)2 and CaCO3 won't dissolve or at least they won't dissolve well.
2. My choice would be AgNO3, because then you can identify the compund by the Ag+ + anion precipitate (only Al(NO3)3 won't give you any reaction)
3. One problem: I have no idea how you will tell the difference between amonium chloride and zinc chloride.

[Donaldson Tan]

3. One problem: I have no idea how you will tell the difference between amonium chloride and zinc chloride.

Once you have identified sodium bicarbonate, you can use it as a source of OH- to precipitate Zinc. Ammonium chloride will give you negative observation

[AWK]

1. Prepare water solutions from your samples. Two compounds are insoluble. They can be identified by HCl (bubles of CO2 for CaCO3)
2.  Phenolphtalein test - you will identify KOH
3. To samples of other 7 solutions add AgNO3 - you can obtain 6 precipitates from which 3 (AgI, Ag2S and Ag3PO4) can be identified by colour , other 3 will be white, though they can change color slowly.
4. To the samples of solutions that produce white precipitates with AgNO3 add dropwise NaOH.  Only ZnCl2 will form white precipitate. Zn(OH)2 will dissolve in excess of NaOH. Treat samples of NaHCO3 or NH4Cl with HCl - CO2 bubbles will identify NaHCO3
5. The last solution should contain Al(NO3)3. Check it using NaOH (dropwise).

[sammysue07]

1. Prepare water solutions from your samples. Two compounds are insoluble. They can be identified by HCl (bubles of CO2 for CaCO3)
2.  Phenolphtalein test - you will identify KOH
3. To samples of other 7 solutions add AgNO3 - you can obtain 6 precipitates from which 3 (AgI, Ag2S and Ag3PO4) can be identified by colour , other 3 will be white, though they can change color slowly.
4. To the samples of solutions that produce white precipitates with AgNO3 add dropwise NaOH.  Only ZnCl2 will form white precipitate. Zn(OH)2 will dissolve in excess of NaOH. Treat samples of NaHCO3 or NH4Cl with HCl - CO2 bubbles will identify NaHCO3
5. The last solution should contain Al(NO3)3. Check it using NaOH (dropwise).

Thanks for all of the information, but we can only use one of the solutions.

[Garneck]

Once you have identified sodium bicarbonate, you can use it as a source of OH- to precipitate Zinc. Ammonium chloride will give you negative observation

Well, in that case, she can use the identified KOH too. And using OH- on ammonium chloride will give you an observation - there will be ammonia released and we've got a nasty smell.

[hmx9123]

In case you like more reading, here's a link to yet another of these solution ID problems we've discussed previously.

http://www.chemicalforums.com/index.php?board=2;action=display;threadid=2669&start=0