Experiment 15: IDENTIFYING THE Pb++ BASIC RADICAL PRESENT IN GIVEN INORGANIC SALT
OBJECTIVE:
TO IDENTIFY THE BASIC RADICAL PRESENT IN GIVEN INORGANIC SALT
APPARATUS REQUIRED
- Test tube
- Test tube holder
CHEMICALS REQUIRED
- Dil. HCl
- H2S
- NH4OH
- KI
- H2SO4
- NH4Cl
- K2CrO4
THEORY
Qualitative inorganic analysis is concerned with the detection and identification of radicals present in inorganic salt or a mixture of salts. Inorganic salts are the outcome of the neutralization of acids with base. Each inorganic salt consists of two parts. The part contributed by acid is called acid radical or anion and the part contributed by base is called basic radical or cation. For example, in sodium chloride, which can be obtained by the neutralization of base NaOH with acid HCl, Na+ is the basic radical and Cl– is the acid radical.
PROCEDURE
The original solution was prepared by dissolving the given salt sample in water. The sample was subjected to several tests for the detection of the basic radical of the salt.
OBSERVATION
1. Preliminary test:
a. State: Solid
b. Odour: Odourless
c. Colour: Odourless
d. Solubility: Soluble in water
Group Separation Table
| Experiment | Observation | Inference |
| 1. 2 ml of the original solution was taken in a clean and dry test tube and a few drops of dil. HCl was added to it. | White ppt. is formed | Presence of Group I metal ions (May be Pb++, Hg+, Ag+) |
2. Confirmatory test:
Test of Pb++ ion
| Experiment | Observation | Inference |
| 1. 2 ml of the original solution was taken in a clean and dry test tube and a few drops of dil. H2SO4 was added to it. | White ppt. was formed which was soluble in hot ammonium acetate | Presence of Pb++ |
| 2. 2 ml of the original solution was taken in a clean and dry test tube and a few drops of dil. K2CrO4 solution was added to it. | Yellow ppt. was obtained which was soluble in NaOH solution. | Presence of Pb++ |
| 3. 2 ml of the original solution was taken in a clean and dry test tube and a few drops of dil. KI solution was added to it. | Yellow ppt. was obtained which dissolved when boiled and reappeared when cooled. | Presence of Pb++ |
Reactions involved:
Pb^{++} + H_{2}SO_{4} \rightarrow \underset{White\ ppt.}{PbSO_{4}} + 2H^{+}\\
Pb^{++} + K_{2}CrO_{4} \rightarrow \underset{Yellow\ ppt.}{PbCrO_{4}} + 2H^{+}\\
Pb^{++} + 2KI \rightarrow \underset{Yellow\ ppt.}{PbI_{2}} + 2H^{+}\\
RESULT
Hence, the sample was identified as Pb++ basic radical.
CONCLUSION
Hence, we can test the basic radicals of a salt by wet ways testing the original solution with several reagents.
PRECAUTION
- Concentrated solutions should be handled carefully.
- The colour of the precipitate should be observed carefully.
- Check whether the original solution is clear and transparent.
