APPARATUS REQUIRED
i. Test tubes
ii. Test tube stand
iii. Test tube holder
iv. Tong
CHEMICALS REQUIRED
i. Silver Nitrate (AgNO3)
ii. Ammonia solution (NH4OH)
iii. Nitric Acid (HNO3)
iv. Barium sulphate (BaSO4)
THEORY
(credit: http://www.wisegeek.com/what-does-a-chemistry-assistant-do.htm)
Qualitative analysis is the process of determining what the substance is actually made of. Qualitative analysis of an inorganic salt is the detection of acid and basic radicals of a salt by suitable methods. A salt is the compound formed by complete or partial neutralization of acid by a base. Salts are strong electrolytes. When dissolved in water they are almost completely dissociated into positively and negatively charged ions.
Acid radicals are the negatively charged radical ions of the salt. These radicals are obtained in salt from acid during neutralization reaction. Examples of such radicals are Cl-, SO4--, NO3-, CO3-- etc. Basic radicals are positively charged radicals in the salt which are obtained in the salt from the base during neutralization reaction. Examples are Mg++, Na+, Ca++etc.
The OH- radical although being negative, is not an acidic radical basic, because it is derived from base. Similarly, H+radical is not basic but it is acidic, because it is derived from acid.
The method of performing chemical tests in the form of solution by dissolving the substance in a suitable solvent is called wet ways. During wet test, the radicals are detected from the solution generally by observing the characteristics colour of the precipitate or solution or gas formed after the ionic interaction with suitable reagents.
OBSERVATIONS
Sample A1
Physical Properties
State – Amorphous Solid
Colour – White
Odour – Characteristic
Solubility – Soluble in cold water
PROCEDURE
Original solution (OS) was prepared by dissolving the given salt sample in water. The sample was subjected to several tests for the detection of acidic radical of the salt.
OBSERVATION TABLE
Halide ion test
| Experiment | Observation | Inference |
|---|---|---|
| Few ml of the OS was taken in test tube and drops of dil. HNO3 was added and boiled. Then, few drops of AgNO3 solution was added. | No ppt. was formed. | Absence of halide ions in the salt. |
Barium Chloride test
| Experiment | Observation | Inference |
|---|---|---|
| The original solution was taken in a test tube and reacted with BaCl2 solution. | White ppt was formed. This ppt. was dissolved readily on the addition of dil. HCl in the solution with the evolution of CO2 gas detected by lime water. | Presence of SO4-- or CO3-- or SO3--. |
Presence of CO3--.
REACTIONS INVOLVED
CO3-- + BaCl2+ BaCO3↓ (white ppt.) + 2Cl-
BaCO3 + HCl -> BaCl + H2O + CO2↑
RESULT
Thus, the sample A1 was inferred to contain acidic radical CO3--.
CONCLUSION
Thus, we can test the acidic radicals of a salt by wet ways testing the original solution with several test reagents step by step.
PRECAUTIONS
i. Concentrated H2SO4 should be handled carefully.
ii. Colour of precipitates should be observed carefully.
iii. During the addition of FeSO4 in the ring test, it should be done without disturbing the tube.
iv. Apparatus should be handled carefully.
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