The qualitative analysis of organic compounds involves identifying their composition and structure. Organic compounds are primarily composed of carbon (C), hydrogen (H), and oxygen (O), but they may also contain elements such as nitrogen (N), sulfur (S), halogens (F, Cl, Br, I), and phosphorus (P). The analysis provides insight into the functional groups, elements, and molecular structure of the compounds, forming a basis for understanding their properties and applications.
1. Preliminary Examination
2. Detection of Elements
The Lassaigne’s Test is a widely used method to detect elements like nitrogen, sulfur, and halogens in organic compounds. In this test, the compound is fused with sodium to convert elements into ionic forms that can be easily detected.
| Element | Test | Observation |
| Nitrogen | Sodium extract + Ferrous sulfate + Ferric chloride + HCl | Prussian blue color (ferric ferrocyanide). |
| Sulfur | Sodium extract + Lead acetate | Black precipitate of lead sulfide (PbS). |
| Halogens | Sodium extract + Silver nitrate (after acidifying with HNO₃) | White ppt (Cl⁻), pale yellow ppt (Br⁻), yellow ppt (I⁻). |
Functional groups are identified using specific chemical reagents.
| Functional Group | Reagent/Test | Observation |
| Alcohol | Lucas Test | Turbidity on reaction with ZnCl₂ + HCl. |
| Aldehyde | Fehling’s Test, Tollen’s Test | Red ppt (Cu₂O), Silver mirror (Ag). |
| Carboxylic Acid | Sodium bicarbonate | Effervescence due to CO₂ gas release. |
| Amine | Hinsberg Test | Formation of precipitates in different layers. |
The information gathered from preliminary and chemical tests is combined with spectroscopic techniques like NMR or IR to confirm the compound's structure.
A buffer solution resists changes in pH when small amounts of acid or base are added. Buffer solutions are essential in various chemical and biological systems to maintain stable pH levels. They play a critical role in industrial processes, research, medicine, and biochemistry.
Types of Buffer Solutions
Buffer solutions work on the principle of equilibrium. When an acid (H⁺) or base (OH⁻) is added, the buffer's components react to neutralize the added substance, preventing significant pH changes.
| Addition | Reaction in Acidic Buffer | Reaction in Basic Buffer |
| Acid (H⁺) | CH₃COO⁻ + H⁺ → CH₃COOH | NH₄⁺ + OH⁻ → NH₃ |
| Base (OH⁻) | CH₃COOH + OH⁻ → CH₃COO⁻ + H₂O | NH₄Cl + OH⁻ → NH₄OH |
Buffer solutions are prepared by combining a weak acid or base with its salt. The ratio of the components can be adjusted to achieve the desired pH. Below are the steps to prepare different types of buffer solutions:
1. Acidic Buffer
2. Basic Buffer
| Buffer Type | Components | Example |
| Acidic Buffer | Weak acid + Salt | Acetic acid + Sodium acetate |
| Basic Buffer | Weak base + Salt | Ammonium hydroxide + Ammonium chloride |
Buffer solutions are widely used due to their ability to maintain stable pH. Some of the key applications are:
1. Biochemical Applications
2. Industrial Applications
3. Research and Laboratory Use
| Factor | Effect on Buffer |
| Buffer Capacity | Depends on the concentration of the acid/base pair. |
| Buffer Range | Determined by the pKa value of the weak acid/base. |
| Temperature | Higher temperatures can disrupt buffer equilibrium and efficiency. |
Buffer pH is calculated using the Henderson-Hasselbalch Equation:
For Acidic Buffers
pH = pKa + log ([Salt]/[Acid])
For Basic Buffers
pOH = pKb + log ([Salt]/[Base])
To find pH from pOH, use the formula: pH = 14 - pOH.
Buffer Example: Blood Buffer System
The blood maintains its pH through the bicarbonate buffer system:
HCO₃⁻ + H⁺ ↔ H₂CO₃ ↔ H₂O + CO₂
Mechanism: Excess H⁺ ions are neutralized by bicarbonate (HCO₃⁻), while excess OH⁻ ions are neutralized by carbonic acid (H₂CO₃). This system keeps blood pH between 7.35 and 7.45, essential for normal physiological processes.
Buffer solutions are indispensable in chemistry, biology, and industry. They ensure pH stability, enabling optimal conditions for reactions, processes, and systems. Understanding their preparation, application, and factors influencing their function is critical for scientific advancements and practical applications.
A part of the fusion solution is acidified with dilute nitric acid. Excess silver nitrate solution is then added, and the formation of a precipitate shows the presence of halogens.
The analysis of the species present in a particular substance is known as qualitative analysis. For example, if a compound is examined, the qualitative analysis would focus on identifying the elements and ions present rather than establishing how much of each is there.
Qualitative analysis identifies the elements and functional groups present in organic compounds. It involves tests like Lassaigne's test for detecting nitrogen, sulfur, and halogens.
A buffer solution resists changes in pH when acids or bases are added. The two types are acidic buffers (e.g., acetic acid and sodium acetate) and basic buffers (e.g., ammonium hydroxide and ammonium chloride).
The Henderson-Hasselbalch equation calculates the pH of buffer solutions using the ratio of the concentrations of the salt and weak acid or base.
Buffer capacity, pH range, temperature, and the concentration of the acid-base pair influence a buffer solution’s efficiency.