Solving Solubility: Experimental Insights into Organic Compound Behavior

Solvation, the process of dissolving, involves disrupting and reestablishing attractive forces between solute and solvent particles. Solubility, defined as the solute amount that can dissolve in a specific amount of solvent at a given temperature, adheres to the principle of "like dissolves like." This implies that polar solutes dissolve in polar solvents, and nonpolar solutes dissolve in nonpolar solvents. Numerous factors, such as the nature/polarity of compounds, temperature, molecular weight, compound structure, acidity/basicity, and intermolecular forces, influence solubility. The overall pressure also plays a role in solute dissolution.

By the experiment's conclusion, students aim to determine the solubility, acidity, and basicity of various organic compounds, including alanine, aniline, benzamide, benzoic acid, chlorobenzene, cyclohexane, ethylacetate, hexane, E-/α-naphthol, dimethylamine, phenol, salicylic acid, and sulfanilic acid. Understanding compound solubility is crucial for identifying and analyzing unknowns in laboratories, providing essential information about a compound's structural composition, particularly in Organic Chemistry, and enhancing comprehension for future experiments and studies.

Following the provided solubility diagram and results table, students classified the solubility of sample solutes, using water, ether, litmus (to assess acidity/basicity), 5% NaOH, 5% NaHCO3, 5% HCl, and concentrated H2SO4 as solvents.

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One drop of liquid or 5mg of powdered solid sample dissolved in 0.2mL solvent was used for the solubility tests conducted in 5mL test tubes.

Various solvents play distinct roles in classifying the solubility of organic compounds, including water, ether, sodium hydroxide, sodium bicarbonate, hydrochloric acid, and sulfuric acid. Water categorizes compounds as soluble if polar and insoluble if otherwise. Ether classifies compounds into acidic, basic, or neutral categories.

Sodium hydroxide identifies soluble compounds as acids, while sodium bicarbonate distinguishes strong and weak acids. Hydrochloric acid categorizes compounds as bases, and sulfuric acid classifies them as either neutral or inert. Organic compounds are thus grouped into ten categories based on their solubility characteristics:

1. 1. SA Group (Water-Soluble Acids): Partially polar compounds soluble in both water and ether, turning blue litmus to red. Example: Methylamine.
   2. SB Group (Water-Soluble Bases): Electron pair donors, turning red litmus to blue. Example: Methylamine.
   3. SN Group (Water-Soluble Neutral): Partially polar compounds like monofunctional alcohols, aldehydes, ketones, esters, nitriles, and amides, soluble in water and ether. Example: Ethylacetate.
   4. S2 Group (Ether-Insoluble): Polar compounds like amine salts, carboxylic acid salts, polyhydroxy alcohols, polycarboxylic acids, hydroxy acids, amino acids, and carbohydrates. Example: Alanine.
   5. AS Group (Strong Acidic): Strong proton donors, insoluble in water but soluble in 5% NaOH and 5% NaHCO3, forming water-soluble salts. Examples: Benzoic acid, Salicylic acid, Sulfanilic acid.
   6. AW Group (Weak Acidic): Includes phenols, enols, primary and secondary nitro compounds, and sulfonamides of primary amines. Soluble in 5% NaOH but insoluble in water and 5% NaHCO3. Examples: Phenol, E-/α-naphthol.
   7. B Group (Basic): Electron pair donors forming hydroxide anions in aqueous solutions. Examples: Aniline.
   8. NM Group (Miscellaneous Neutral): Compounds with sulfur and nitrogen, like aromatic nitro compounds, nitriles, amides, and sulfanomides of secondary amines. Example: Benzamide.
   9. N Group (Neutral): Compounds mainly containing oxygen and lacking sulfur or nitrogen. Examples: Alcohols, aldehydes, anhydrides, esters, ethers, ketones, unsaturated hydrocarbons.
   10. I Group (Inert): Compounds like alkyl and aryl hydrocarbons, saturated hydrocarbons, and diaryl ether. Examples: Chlorobenzene, Cyclohexane, Hexane.

Table 1: Solubility of Different Solutes and Solvents

Solvation, the process of dissolving, involves the disruption and reestablishment of attractive forces between solute and solvent particles. Solubility, the amount of solute that can dissolve in a specific amount of solvent at a given temperature, follows the "like dissolves like" principle, where polar solutes dissolve in polar solvents and nonpolar solutes in nonpolar solvents. This experiment aims to classify the solubility of various organic compounds, considering factors like polarity, molecular weight, structure, acidity, and basicity.

The solubility tests were conducted using water, ether, litmus, 5% NaOH, 5% NaHCO3, 5% HCl, and concentrated H2SO4 as solvents. Liquid samples or 5mg of powdered solid samples were dissolved in 0.2mL of the respective solvents in 5mL test tubes.

Results and Discussion

1. Rationale Behind Solubility Classes:
   • SA (Water-Soluble Acid): Partially polar compounds soluble in water and ether, turning blue litmus to red.
   • SB (Water-Soluble Base): Partially polar compounds soluble in water and ether, turning red litmus to blue.
   • SN (Water-Soluble Neutral): Partially polar compounds soluble in water and ether, no litmus change.
   • S2 (Ether-Insoluble): Very polar compounds soluble in water but insoluble in ether.
   • AS (Strong Acidic): Nonpolar, insoluble in water, soluble in 5% NaOH and 5% NaHCO3, forming water-soluble salts.
   • AW (Weak Acidic): Nonpolar, insoluble in water, soluble in 5% NaOH, insoluble in 5% NaHCO3.
   • B (Basic): Good electron pair donors, form hydroxide anions in aqueous solution, react with acids to form salts.
   • NM (Miscellaneous Neutral): Contain sulfur or nitrogen, undergo hydrolysis and reduction upon heat.
   • N (Neutral): Contain oxygen without sulfur or nitrogen, unsaturated and easily sulfonated.
   • I (Inert): Do not undergo sulfonation.
2. Diagram and Solubility Classification: [Refer to the provided diagram]

   Table 2: Solubility Classification

   • SA: none - monofunctional polar compounds (e.g., carboxylic acids)
   • SB: Methylamine - monofunctional polar compounds (e.g., amines)
   • SN: Ethylacetate - monofunctional polar compounds (e.g., alcohol, aldehyde, ketone, ester, amides, nitriles)
   • S2: Alanine - polycarboxylic acids; amine salts; metal salts of carboxylic acids; ammonium salts; di- and polyfunctional compounds
   • AS: Benzoic acid, Salicylic acid, Sulfanilic acid - carboxylic acids; sulfonic acids; phenols substituted with polyhalide nitro group and aldehyde groups
   • AW: Phenol, E-/α-naphthol - phenols; enols; primary and secondary nitro compounds; sulfonamides of primary amines
   • B: Aniline - primary, secondary, tertiary amines except di- and triaryl amines, hydrazines, N,N-dialkyl-carboxamides
   • NM: Benzamide - nitriles; amides; sulfanomides of secondary amines; aromatic nitro compounds
   • N: none - neutral polar compounds (e.g., alcohols, aldehydes, anhydrides, esters, ethers, ketones, unsaturated hydrocarbons)
   • I: Chlorobenzene, Cyclohexane, Hexane - alkyl and aryl halides; aromatic hydrocarbons; saturated hydrocarbons; diaryl ether

Compound solubility is influenced by factors like polarity, molecular weight, structure, intermolecular forces, acidity, and basicity. The "like dissolves like" principle governs solvation, indicating higher solubility between polar solutes and solvents or nonpolar solutes and solvents.

It is crucial for students to handle reagents carefully to prevent contamination, ensuring accurate and reliable results.