Ariel Chen

Qualitative Analysis of Cations Lab Report

Known Solution Unknown Solution (#1)

Step Procedure Results Conclusion Results Conclusion

1

Add HCl to known solution in TT1.

Centrifuge. Pour colored solution

into TT2.

White ppt

forms. Other

ions present

in solution in

TT2

Ag+, Pb

2+,

and/or

Hg22+

present

White ppt

forms. Other

ions present in

solution in TT2

Ag+, Pb

2+,

and/or

Hg22+

present

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.

Yellow

precipitate Pb

2+ present

Yellow

precipitate Pb

2+ present

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.

Black residue Hg2

2+

present

No white ppt

from Step 2

Hg22+

and

Ag+

both

absent

4

Add HNO3 to the solution from

Step 3 until the solution is acid or a

permanent white precipitate is

formed.

White

precipitate Ag

+ present

5

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. Centrifuge and

separate the solution into another

test tube. Set the solution aside for

Procedure 10. Treat the precipitate

by Procedure 6.

Colored ppt Fe

3+ and/or

Al3+

present Colored ppt

Fe3+

and/or

Al3+

present

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

excess. Precipitates. Centrifuge and

separate the solution into another

test tube. Set the solution aside for

Procedure 8. Treat the precipitate by

Procedure 7.

Precipitate

forms

Precipitate:

Fe(OH)3

Precipitate

forms

Precipitate:

Fe(OH)3

7

Dissolve the precipitate from

Procedure 6 by adding dilute 6-M

HC1 dropwise. Stir. Add three drops

Deep red

color:

Fe(SCN)2+

Fe3+

present Deep red color:

Fe(SCN)2+

Fe

3+ present

Ariel Chen

Qualitative Analysis of Cations Lab Report

Unknown Solution #1

Ions present: Al3+

, Fe3+

, Pb2+

Ions absent: Ag+

, Hg22+

, 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)

Fe3+

(aq) + 6NH3(aq) → Fe(NH3)63+

(aq)

6. Al(OH)3 (s) + OH- (aq) ---- > Al(OH)4

- (aq)

Al(OH)3 + 3H2O + 3H+ ---> [Al(H2O)6]

3+

of 0.1-M KSCN solution.

8

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

adding

NH3 solution. White/gray ppt.

Centrifuge and separate the

solution. Discard the solution and

treat the precipitate by Procedure 9.

White/gray

ppt Al(OH)3 White/gray ppt Al(OH)3

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

NH3 solution until the solution is

just basic. Stir. Check

with litmus. Warm the solution in a

water bath.

Red ppt

(“lake”) Al

3+ present

Red ppt

(“lake”) Al

3+ present

10

Add 10 to l5 drops of

dimethylglyoxime to the solution

from Procedure 5. Warm in a water

bath.

Red ppt Ni+ present No ppt Ni

+ absent