Qualitative analysis of cations lab report.docx

Ariel Chen Qualitative Analysis of Cations Lab Report

Step

Procedure

1

Add HCl to known solution in TT1. Centrifuge. Pour colored solution into TT2.

2

Add 2 ml of distilled water to the  precipitate and place the test tube in a boiling water bath for three minutes. Stir. Centrifuge for a few seconds. Pour the supernatant liquid into another test tube. Immediately add two drops of K2CrO4 to the liquid.

3

Add one ml of NH3 to the white  precipitate from Step 2. Stir. Black  residue. Centrifuge, then decant the solution into another test tube and discard the black residue.

4

5

6

7

Known Solution Results Conclusion White ppt + 2+ Ag , Pb , forms. Other  and/or  ions present 2+ Hg2 in solution in  present TT2

Yellow  precipitate

Add HNO3 to to the solution from from Step 3 until the solution is acid or a White  permanent white precipitate is  precipitate formed.  Neutralize the solution from  procedure 1 (TT2) by adding NH3 solution until the solution is basic. Check with litmus paper after  stirring thoroughly. Add one ml in excess. Add one ml of NH4Cl. Colored ppt Colored ppt. Centrifuge and separate the solution into another  test tube. Set the solution aside for  Procedure 10. Treat the precipitate  by Procedure 6. Dissolve the precipitate from Procedure 5 by adding 6-M HC1 dropwise. Stir añer each addition. Make basic to litmus with 6-M  NaOH. Stir. Then add 1-2 ml in Precipitate excess. Precipitates. Centrifuge and forms separate the solution into another  test tube. Set the solution aside for  Procedure 8. Treat the precipitate by Procedure 7. Dissolve the precipitate from Deep red Procedure 6 by adding dilute 6-M color: 2+ HC1 dropwise. Stir. Add three drops Fe(SCN)

+

2+

White ppt forms. Other  ions present in solution in TT2

Ag , Pb , and/or  2+ Hg2  present

Yellow  precipitate

Pb

 No white ppt from Step 2

Hg2 and + Ag  both absent

Fe and/or  3+ Al  present

Colored ppt

Fe and/or  3+ Al  present

Precipitate: Fe(OH)3

Precipitate forms

Precipitate: Fe(OH)3

2+

Pb

present

2+

Black residue

Unknown Solution (#1)  Results Conclusion

Hg2  present

2+

present

2+

+

Ag  present

3+

3+

Fe

present

3+

Deep red color: 3+ Fe present 2+ Fe(SCN)

Ariel Chen Qualitative Analysis of Cations Lab Report

8

9

10

of 0.1-M KSCN solution. Acidify the solution from Procedure 6 by adding dilute HC1 dropwise. Stir after each addition and check with litmus. Add drops of NH4Cl and make basic by White/gray adding  ppt  NH3 solution. White/gray ppt. Centrifuge and separate the solution. Discard the solution and treat the precipitate by Procedure 9. Dissolve the precipitate from Procedure 8 by adding dilute 6-M HCl dropwise. Stir. Add one ml of  the aluminon test reagent. Add 6-M Red ppt  NH3 solution until the solution is (“lake”)  just basic. Stir. Check  with litmus. Warm the solution in a water bath. Add 10 to l5 drops of  dimethylglyoxime to the solution Red ppt from Procedure 5. Warm in a water   bath.

Al(OH)3

3+

Al  present

+

Ni present

White/gray ppt

Al(OH)3

Red ppt (“lake”)

Al  present

No ppt

Ni absent

3+

+

Unknown Solution #1 3+ 3+ 2+ Ions present: Al , Fe , Pb + 2+ + Ions absent: Ag , Hg2 , Ni Discussion -

1. Cl is the precipitating reagent for the silver group. A solution of NaCl would also work as well, because it  provides the chloride ion in solution. 2. Ag+(aq) + Cl-(aq) →AgCl(s) AgCl(aq) + 2NH3(aq) → Ag(NH3)2(aq) + Cl-(aq) Ag(NH3)2+(aq) + Cl-(aq) + 2H+(aq) → AgCl(s) + 2NH4+(aq) 3. Hg + e ←→ Hg Hg ←→ Hg² + e 4. AgCl(s) ←→ Ag+(aq) + Cl-(aq) AgCl(s) + 2 NH3(aq) ←→Ag(NH3)2+(aq) + Cl-(aq) 5. Fe3+(aq) + 3NH3(aq) + 3H2O --> Fe(OH)3(s) + 3NH4+(aq) 3+ 3+ Fe (aq) + 6NH3(aq) → Fe(NH3)6 (aq) 6. Al(OH)3 (s) + OH- (aq) ---- > Al(OH)4- (aq) Al(OH)3 + 3H2O + 3H+ ---> [Al(H2O)6]3+ ⁺ ⁺

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