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Instruction for unknown 9A/9B
Possible ions:1. Cations: Na+, K+, NH4+, Ca2+, Mg(OH2)62+, Al(OH2)63+Zn(OH2)62+, Ag(OH2)2+,Cu(OH2)62+
2. Anions: HO-, CO32-, HCO3-, SO42-, HSO4-, NO3-, Cl-, HS-, O2-
3. Possible insoluble substance: Ca(OH)2, CaSO4•2H2O, CaCO3, MgCO3, Mg(OH)2AgCl, Ag2O, Ag2CO3, Ag2S, Ag2SO4, ZnS, Zn(OH)2, CuO, CuS, CuCO3
4. Alums
Notes:--9A (the sample with the numerical label) is a pure salt, which means it only containstwo (one cation and one anion) or three (alums, i.e., two cations and SO42−) ions.--The insoluble substance could be one or more kinds of the above compounds.They will not issue Zn(OH)2/ ZnS in the same sample, nor would a MgCO3/ Mg(OH)2
be issued.Possible Ionsi) Cations: Na+, K+, NH4
+, Ca2+, Mg(H2O)62+, Al(H2O)63+
ii) Anions: Cl−, NO3−, SO4
2-, HSO4-, OH−, CO3
2-, HCO3−
iii) Possible INSOLUBLE compounds: Ca(OH)2, CaSO4•2H2O, CaCO3, MgCO3, Mg(OH)2
1) Flame Test
* Use pea-sized solid + 5 drops 1M HNO3 (stir!) – Watch out forbubbles!*
Intense yellow: Na+ (K+, NH4+, Ca2+, Mg(H2O)6
2+, Al(H2O)63+ possible)
Red or red orange: Ca2+ (No Na+, others may be present)Purple: K+ (No Na+ and Ca2
+, others may be present)No color: possibly NH4
+, Mg(H2O)62+, Al(H2O)63+ (No Na+, K+, Ca2+)
Green: Cu(OH2)62+
Color:__________________________________
CO32- or HCO3
-
pinch of unknown with ~3 drops of 6M HNO3
Reasoning:If you see bubbles, either CO3
2- or HCO3- is present (remember that carbonates
interfere with flame test of solid Na and Ca salts)
Color:________________________________
2) Test for NH4+
Place a small portion of original sample in a test tube, then add a few drop of 6M NaOH solution. Stir well then do sniff test (reliable and fast!); optional: do the litmus test (Red to blue).
Litmus Results:_____________________________
Sniff Results:______________________________
S2-/HS- Testo Place original sample in a spot plate and add a few drops of 2M
H2SO4, if arotten egg smell w/ bubbles, then S2- or HS- is present
_____________________________________
3) pH Test
pH:_______________
Meaning: ~1-2 HSO4
- (No HCO3-, CO3-, OH-)~3 (or lower) Al(H2O)6
3+ (No HCO3-, CO3
-, OH-)~5 (or lower) NH4
+, Mg(H2O)62+
~7 Cl-, NO3-, SO4
2-, K+, Na+, Ca2+ (Note: neutral ions may be present at any pH)~8.5 HCO3
- (No HSO4-, Al(H2O)6
3+, OH−)~12 CO3- (No HSO4
-, Al(H2O)63+, NH4
+)≥13 OH− (No HSO4
- Al(H2O)63+, HCO3
-, NH4+)
**If your sample has an insoluble compound, you just use the saturated supernatant liquid to testpH. pH for insoluble compounds**Ca(OH)2: ~ 12.6CaSO4•2H2O: ~ 7.0CaCO3: ~ 10.0MgCO3: ~ 9.5Mg(OH)2: ~ 10.5
Make solution4. Make SolutionDissolve 2/3 of sample with 10 mL deionized water. Stir well with a clean stirring rod for20-30 seconds. Get a small amount of the supernatant and test its pH with pH paper (toget the approximate pH), and indicator (to get the exact pH if needed).
• For 9A (which is a pure compound): 9A is either soluble or not, and cannot be
both.Case 1: If the sample is soluble in water, then test the solution for cation
and anion(s).(Go to guide #1)
Case 2: If the sample is insoluble, then just test the insoluble compound. Discard the
supernatant (liquid portion). (Go to guide #2)
• For 9B (which may be a mixture),Case 1: If the sample is FULLY soluble in water, then test solution for
cation(s) andanion(s).
Case 2: If it is insoluble or partially soluble, separate the solid from the supernatant
by using a centrifuge. Do not discard anything.a. Test the supernatant for cation(s) and anion(s). Go to guide #1.b. Test the insoluble portion. Go to guide #2.
Guide 1: Soluble Portion (Cations and Anions)A. Cation Test
Na+, K+, NH4+, Ca(OH2)6
2+,
Al(OH2)63+, Zn(OH2)6
2+,
Cu(OH2)62+, Ag(OH2)2+
Add 1 M NaCl dropwise (if no ppt forms after several drops, then no Ag)
If ppt formed, add excess NaCl and remove AgCl ppt. by centrifuge. Keep the supernatant(liquid)
To the supernatant, add excess 6M NH3. Centrifuge.
Liquid: Na+, K+, NH4+, Ca(OH2)6
2+,
Al(OH2)63+, Zn(OH2)6
2+, Cu(OH2)62+,
PPT: Al(OH2)3(OH)3, Mg(OH)2
Add 2-4 mL TAA+NaAc+ heat (water bath)
Add excess 2 M NaOH
Soln: K+, Ca+
Ppt: CuS, ZnS
Add excess NaCO3 Add excess 2 M H2SO4
Ppt: CaCO3 Soln: K+
Test for NH4 w/ litmus, burn off NH4, test for K+ with cobaltinitratePpt: K+ present Soln: Zn2+ ,odor Black ppt: CuSAdd NaCO3Ppt: ZnCO3
White Ppt: Mg(OH)2
Soln: Al(OH2)2(OH)4-
Add excess saturated NH4Ppt: Al(OH)3
B. Anion Test• Cl-: Acidify with 3-6 drops 6M HNO3 then add AgNO3. If ppt. forms, then
Cl ispresent.
• SO42- and HSO4-: acidify with 3-6 drops 6M HNO3, then add Ba(NO3)2. ppt =HSO4-/SO42- Go back to the pH result to determine what sulfate is
present.• NO3-: cover ferrous ammonia sulfate w/ solution. Add 3 drops 18M
H2SO4. Red-brown ppt = NO3 presence.
• OH-: Go back to the pH result.
Guide 2: Insolubles
A. Observe the color of the insoluble portion• White: Ca(OH)2*, CaCO3*, CaSO4, Mg(OH)2*, Zn(OH)2*, ZnCO3, ZnO*,
ZnS*,AgCl, Ag2SO4 (soln in hot water?), MgCO3
• Black: CuO, CuS, Ag2O, Ag2S• Dark Green: Ag2CO3
• Blue: CuCO3
*Soluble in 1M HNO3
B. Chemical test for insolubles (based on the color of the solid you have)• Insoluble tests
o Dark brown, black, or dark green, CuCO3, CuO, CuS, Ag2CO3, Ag2O,Ag2S
CuCO3
CuO
CuS
Ag2CO3
Ag2O
AgS
Dissolved: Ag2 (add 1M NaCl to check)
CuO (Blue Solution)
Bubbles and dissolved:
Ag2CO3 (yellow soln, use NaCl to check)
CuCO3 (blue solution)
Nothing: Ag2S (+15 M HNO3- colorless or yellow soln)
CuS (+15 M HNO3=blue solution)
Add 2 M HNO3
(hot water bath T)
o White salts – Ca(OH)2, CaSO4*2H2O, CaCO3, Mg(OH)2, MgCO3
• Flame test – treat solid w/ 1M HCl, stir, and do a flame test.
• If flame is red-orange, then Ca2+ is present (If you are not certain repeat
flame test, but this time use 6M HCl). Then determine which is present
based on solubility in 1M HCl
• If flame is colorless, do following chart:
Ca(OH)2
CaSO4*2H2O
CaCO3
Treat with
1 M HCl
Dissolved- Ca(OH)2
Nothing- CaSO4*2H2O
Dissolves with bubbles- CaCO3
Mg(OH)2
MgCO3
Zn(OH)2
ZnCO3
ZnS
AgCl
AgSO4
Treat w/
2M H2SO4
Dissolves- Mg(OH)2, Zn(OH)2
Dissolves with bubbles- MgCO3, ZnCO3
Dissolves ZnS (rotten egg smell)
AgSO4 (no smell)
Nothing- AgCl
