Title: Analysis of Inorganic Salt (NH₄Cl) – Step-by-Step Procedure
Introduction
Ammonium chloride (NH₄Cl) is an inorganic salt that consists of ammonium (NH₄⁺) and chloride (Cl⁻) ions. Its identification and analysis involve qualitative and quantitative techniques to confirm its composition and properties.
Step-by-Step Analysis of NH₄Cl
1. Preliminary Examination
| Property | Observation |
|---|---|
| Solubility | Soluble in water, slightly soluble in alcohol. |
| Odor | Emits ammonia odor when heated. |
| Physical Appearance | White crystalline solid. |
2. Dry Heating Test
| Procedure | Observation | Inference | Chemical Equation |
| Heat a small amount in a dry test tube. | White fumes and sublimation. | Confirms presence of ammonium salts. | NH₄Cl → NH₃ + HCl (sublimation) |
3. Flame Test
| Procedure | Observation | Inference |
| Moisten platinum wire, dip in NH₄Cl, and place in flame. | No characteristic flame color. | NH₄Cl does not impart a flame color. |
4. Identification of Ammonium Ion (NH₄⁺)
a. Nessler’s Reagent Test
| Procedure | Observation | Inference | Chemical Equation |
| Add Nessler’s reagent to sample solution. | Brown precipitate forms. | Confirms presence of NH₄⁺ ions. | NH₃ + 2[K₂HgI₄] + 3KOH → HgO·Hg(NH₂)I (brown ppt) + 7KI + H₂O |
b. Sodium Hydroxide (NaOH) Test
| Procedure | Observation | Inference | Chemical Equation |
| Add NaOH to NH₄Cl solution and warm gently. | Pungent smell of ammonia (NH₃). | Confirms presence of NH₄⁺ ions. | NH₄Cl + NaOH → NH₃ + NaCl + H₂O |
c. Litmus Paper Test
| Procedure | Observation | Inference | Chemical Equation |
| Hold moist red litmus near the test tube after adding NaOH. | Red litmus turns blue. | NH₃ gas evolved, confirming NH₄⁺ ions. | NH₃ + H₂O ⇌ NH₄⁺ + OH⁻ |
5. Identification of Chloride Ion (Cl⁻)
a. Silver Nitrate (AgNO₃) Test
| Procedure | Observation | Inference | Chemical Equation |
| Add HNO₃ followed by AgNO₃ to NH₄Cl solution. | White precipitate of AgCl forms. | Confirms presence of Cl⁻ ions. | NH₄Cl + AgNO₃ → AgCl (white ppt) + NH₄NO₃ |
b. Lead(II) Nitrate (Pb(NO₃)₂) Test
| Procedure | Observation | Inference | Chemical Equation |
| Add Pb(NO₃)₂ to NH₄Cl solution. | White precipitate of PbCl₂ forms. | Confirms presence of Cl⁻ ions. | 2NH₄Cl + Pb(NO₃)₂ → PbCl₂ (white ppt) + 2NH₄NO₃ |
6. pH Test
| Procedure | Observation | Inference | Chemical Equation |
| Dissolve NH₄Cl in distilled water and test with pH paper. | Slightly acidic pH (~5-6). | NH₄Cl is a weak acid due to NH₄⁺ hydrolysis. | NH₄⁺ + H₂O ⇌ NH₃ + H₃O⁺ |
Conclusion
The qualitative analysis of NH₄Cl confirms the presence of ammonium (NH₄⁺) and chloride (Cl⁻) ions through various chemical tests. Its solubility, sublimation, and reaction with different reagents provide conclusive evidence of its identity. This systematic analysis is essential in inorganic chemistry for identifying unknown salts accurately.