Saturday, January 12, 2013

Qualitative Analysis Step-By-Step simple instructions

These instructions are boiled down and simplified from the lab book in class CHE 120. These instructions should be used hand-in-hand with the Data Sheet

I've found that when I go into lab with these condensed instructions, I tend to finish faster than trying to go directly from the lab book. Hope it helps you too!

Group 1
1.       Step 1:
a.       Cool test tube in ice bath
b.      5 drops 6M HCL (stir with glass rod)
c.       Use cold water to wash down solution that adheres to test tube
d.      Centrifuge
e.      Add additional 6M HCL to ensure that the solution is completely precipitated
f.        Centrifuge
g.       Decant
                                                               i.      Decant contains Group II & III (save for other tests)
2.       Step 2 (Separation of Pb 2+(aq) from Group I Chlorides)
a.       Add 15-20 drops of hot distilled water
b.      Stir well with glass stirring rod until all precipitate is colloidally suspended
c.       Boiling hot water bath for 1-2 minutes
d.      Centrifuge while still hot
e.      Decant
                                                               i.      PPT contains possibly AgCl(s) and HgCl2 (s) (step four)
                                                             ii.      Decant contains Pb2+ (used in step three)
3.       Confirmation of Pb2+
a.       Cool decantate
b.      Divide into two equal portions
c.       Add 1 drop of 0.2 M K2CrO4 to one part (Yellow PPT proves lead)
d.      Add 1 drop of 2 M H2SO4.
e.      Cool the Pb/H2SOSolution (White PPT further confirms lead – may take time)
4.       Separation of Hg2+ and Ag+
a.       To PPT – add 4 drops of 15 M NH3 (aq)
b.      Mix thoroughly
c.       Centrifuge
d.      Decant
                                                               i.      PPT: A gray-black residue (the mixture of Hg and HgNH2Cl) proves mercury ion
                                                             ii.      Decant: add 16 M HNO­ drop-wise to decantate and mix until slightly acidic
1.       Check with litmus paper
                                                            iii.      Formation of white PPT (AgCl) proves silver ion

Group 2
5.       Separation of Group II Cations
a.       15 drops of unknown solution into small casserole
b.      Add 6 drops of 3% H2O2
c.       Add 6 drops of 2 M HCl
d.      Boil down the volume on a hot plate to about 2 – 3 drops
e.      Allow to cool
f.        Add 6 drops of 6 M HCl
g.       Boil contents down to pasty mass (2-3 drops of liquid left)
                                                               i.      DO NOT BAKE THE RESIDUE
                                                             ii.      If too much is boiled off then add 2 drops DI water
h.      Cool
i.         Add 5 drops of 2 M HCl
j.        Swirl acid until entire residue dissolves
                                                               i.      If required, warm slightly and stir
k.       Transfer solution to test tube
l.         Add 8 drops of thioacetamide (CH3CSNH2) and mix thoroughly
m.    Add 8 drops of Hot distilled water
n.      Add 8 more drops of 1 M thioacetamide
o.      Add 1 drop 1 M Ammonium acetate (NHC2H3) mix well
p.      Heat in boiling water bath for 4 minutes
q.      Centrifuge
                                                               i.      PPT contains Group II (PbS Black, Bi2S3 Brown, CuS Black, and CdS Yellow)
                                                             ii.      Decante contains Group III and IV
1.       NOTE: CH3CSNH2 + 2H2O -à CH3COOH + NH3 + H2S
6.       Separation of lead from other Group II
a.       Put PPT from #5 into casserole
b.      Add 10 drops of 16 M HNO3 to a casserole containing residue from #5
c.       Heat until all sulfides have dissolved (no more PPT) – tiny yellow crystal
d.      Add additional 16 M HNO3 if needed
e.      Discard yellow sulfur particles
f.        Add 4 drops of 18 M H2SO4 to casserole
g.       Evaporate carefully under hood (1 – 5 drops remaining – dense white fumes)
h.      Add 15 drops of cold water
i.         Stir contents until all material in casserole is dissolved or suspended;
j.        transfer quickly to test tube
k.       wash casserole dish with four drops of cold water and transfer washing to same test tube
l.         Cool in ice bath
m.    Centrifuge
n.      Decant
o.      Wash PPT twice with 10 drops of cold water (discard decant of washing)
PPT contains PbSO
Decant contains Bi, Cu, Cd
p.      Add to PPT, 4 drops of 1M NH4C2H3O
q.      Stir 30 seconds
r.        Add 2 drops  0.2 M K2CrO4 (yellow confirms lead)
7.       Separation of Bismuth
a.       To decant from step 6 add 15 M NH3 drop wise until alkaline (litmus paper)
b.      Stir 2 minutes
c.       Centrifuge and decant – save decant for step 8
                                                               i.      PPT is bismuth
                                                             ii.      Decant is either Cd or Cu
d.      Wash the PPT twice with 15 drops of hot water
e.      Add 3 drops of 8 M NaOH and 2 drops of 0.2 M SnCl2
f.        Stir – jet black PPT proves Bi
8.       Detection of Copper
a.       If decant from 7 is blue then copper is present (sometimes present when colorless)
b.      Add 5 drops of decantate into a different test tube
c.       Add 5 M acetic acid until decolorized
d.      Add 2 drops of 0.2 M Potassium hexacyanoferrate (K4Fe(CN)6)
                                                               i.      Red PPT confirms Cu
9.       9 Detection of Cadmium
a.       IF Copper is ABSENT
                                                               i.      Treat colorless solution with 2 – 3 drops of Ammonium Sulfide
                                                             ii.      Mix thoroughly
                                                            iii.      Let stand for 1 minute
                                                           iv.      Yellow PPT confirms CdS
b.      If copper is PRESENT
                                                               i.      Add 0.2M KCN (this is poisonous) dropwise, to a 10 drop portion of blue decantate until color disappears
                                                             ii.      Treat solution with 3 drops of Ammonium sulfide solution
                                                            iii.      Mix thoroughly
                                                           iv.      Let stand 1 minute
                                                             v.      Yellow PPT confirms CdS

Group III
10.   Place decant from step 5 into casserole and evaporate down to volume of 8 – 10 drops
a.       Transfer to test tube
b.      Centrifuge
c.       Decant to another test tube
d.      To decant:
                                                               i.      Add 4 drops 2 M NH4Cl
                                                             ii.      Mix thoroughly
                                                            iii.      Add 15 M Aqueous NH3 dropwise (stir) until alkaline
e.      To alkaline mixture add 9 drops of ammonium sulfide solution
f.        Centrifuge (BUT DO NOT DECANT)
g.       Note the color
h.      Heat in boiling water bath
i.         Centrifuge
j.        Add one more (NH4)2S to ensure it is complete
k.       Wash down sides of tube with hot water
l.         Centrifuge again
m.    Note color of supernatant liquid and decant
                                                               i.      Decant contains Group IV ions
n.      To PPT: wash three times with 20-drops of solution
                                                               i.      Solution is equal volume of water and 1 M ammonium acetate
11.   Further process Group III PPT for analysis
a.       Add 10 drops of 12 M HCL
b.      Mix thoroughly
c.       Transfer to casserole
d.      Boil gently 30 seconds
                                                               i.      If PPT is not dissolved, add 3 drops 16 M HNO3
                                                             ii.      Mix thoroughly
                                                            iii.      Boil until solution is obtained (add more HNO3 if needed)
e.      Add 10 drops of cold water
f.        Transfer to test tube
g.       Centrifuge to remove sulfur
h.      Decant into casserole
i.         Make strongly alkaline by adding 8 M NaOH and mix
                                                               i.      If ppt is still mushy/non-fluid then add 10-20 drops of water
j.        Add 2 drops of 3% HO2
k.       Stir for 1 minute
l.         Boil for 2 minutes
m.    Replinish lost water
n.      Transfer to test tube before PPT can settle
o.      Centrifuge
p.      Decant
                                                               i.      PPT : wash three times with hot water and analyze in step 12
                                                             ii.      Decant is discarded
12.   Detection of Iron
a.       To PPT, add 20 drops of 2 M H2SO4 and mix thoroughly
                                                               i.      Transfer to casserole
                                                             ii.      Boil gently 1 minute
                                                            iii.      Add a drop of 3% H2O2
                                                           iv.      Boil for 1 minute after PPT is completely dissolved
                                                             v.      Add 10 drops of water
                                                           vi.      Cool
                                                          vii.      Divide into four equal portions
b.      To one portion, add  1 or 2 drops of 0.2 M KSCN
                                                               i.      Blood red proves iron
13.   Detection of Cobalt
a.       To a second portion, Add 10 drops of 1 M NaF
b.      Mix well
c.       Add 10-20 drops of saturated solution of NH4SCN (ammonium thiocyanate) in ethyl alcohol
d.      Formation of blue solution proves Co2+
14.   Detection of nickel
a.       To third solution, add enough 6 M NH3 to make it basic
                                                               i.      If PPT shows up (Fe(OH)3 or Mn(OH)2) then centrifuge and use the decant
b.      To clear decant, add 2-4 drops of DMG (dimethylgloxime)
c.       Mix thoroughly
d.      Stand for 1 minute
e.      Strawberry red proves Nickel
15.   Detection of Manganese
a.       Dilute fourth portion with equal volume of water
b.      Add 2 drops of 3 M HNO3
c.       Mix thoroughly
d.      Add a few grains of solid sodium bismuthate
e.      Mix thoroughly
f.        Let stand 1 minute
g.       Centrifuge
h.      A pink to reddish purple solution proves Mn

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