Pnhown 2 Unknown Scheme

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Unknown Scheme:
You can use this scheme as a guide when you are making your own. Don't just show up to class with this though.

**SCHEME FOR UKNOWN 2:**

Unknown Scheme: 2

I. Description
A) Phase, solubility, color, odor, shape

II. Flame Test
A) Orange flame  Na+ present (possibly K+, NH4+)
B) Red flame  Ca2+ present (no Na+)
C) Purple flame  K+ present (possibly NH4+)
D) No change in flame color  Ca2+, K+, Na+ absent (possibly NH4 present)

III. pH Test
A) Add a little bit of unknown to a small amount of neutral water
B) Fill several vials with test solution and use indicators to determine pH

Common pHs for Anions and Cations: pH 1.5: HSO4- present; CO32-, HCO3-, OH- not present pH 2.5: SO42- present pH 3-3.5:
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To Separate, add excess 3-6M NH3+ to separate Mg+ and Al2+ from Na+, K+, NH4+, and Ca2+*

*Ca2+ Separation:
A) Treat sample solution with excess 0.5M Na2CO3
B) After ppt. has formed, centrifuge in test tube
C) Treat centrifuged sample with more Na2CO3 and repeat until Ca2+ is out

*Mg(H2O)2+/Al(H2O)3+:
A) If no ppt. forms after addition of NH3, then Mg(H2O)62+ is not present
B) If ppt. forms with NH3, but doesn’t form a ppt. with the addition of excess 2M NaOH, then Mg(H2O)62+ is present and Al(H2O)3+ is absent

IV. NH4+ Test
A) Observe test results for pH test (if acidic, NH4+ could be present)
B) Place about 2-5mL of sample solution in vial and add an equal amount of 1M NaOH to form NH3
C) If smell of NH3 is present, then NH4+ is present and pH test will be that of a basic solution

*Removal of NH4+ (perform only if NH4+ test is
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forms, then Cl- is present

VII. SO42-/HSO4- Test
A) Place several drops of sample solution in vial and add 1M HNO3 until acidic (test acidity with red litmus paper)
B) Add one drop of 0.25M Ba(NO3)2
C) If cloudy ppt. forms, then SO4- is present, unless CO32- is present
D) To distinguish between SO4- and HSO4-, test pH

VIII. NO3- Test
A) Place small crystal of Fe(OH2)6(NH4)2(SO4)2 in a spot plate
B) Cover crystal with a few drops of the sample solution
C) Immediately add 2 drops of 18M H2SO4
D) If brown solution forms, NO3- is present

IX. CO32-/HCO3- Test
A) Treat sample solution with 1M HCl to observe generation of colorless, odorless gas (CO2)
B) To distinguish between CO32- and HCO3-, test pH
C) If test is positive for CO2 and isn’t very soluble in H2O, it is CO32-

Possible Chemicals:
Cations: Ca2+, K+, Na+, NH4+, Mg (H2O)62+, Al (H2O)63+,
Anions: Cl-, NO3-, SO42-, HSO4-, OH-, CO32-, HCO3-
Insoluble Compounds: Ca (OH)2, CaSO4*2H2O, CaCO3, MgCO3 (white), Mg (OH)2,
Alums: Na[Al(H2O)6](SO4)2*6H2O, K[Al(H2O)6](SO4)2*6H2O, NH4[Al(H20)6](SO4)

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