Solubility Lab Mini Report PDF

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Solubility Lab Mini Report...

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Analysis and Application of Solubility Principles in Various Substances Results and Discussion Solubility principles were applied to investigate the solubility of various substances in different solvents and organic acids and bases. Various experiments indicated that polar solutes were readily soluble with polar solvents and nonpolar solutes dissolved easily with nonpolar solvents. On the other hand, polar solutes did not dissolve in nonpolar solvents and vice versa. With different alcohols, more polar alcohols were miscible with the more polar solvent, water, and the less polar alcohols were miscible with the more nonpolar solvent, hexane. Similarly, liquid pairs with similar polarities intermixed into a homogeneous solution while those with different polarities separated and formed two liquid phases. With organic acids and bases, the solubility of the acids and bases depended on the acidity or the basicity of the solvents. Organic acids dissolved readily in basic solvent while they precipitated once the solvent became acidic. Likewise, organic bases precipitated once the solvent turned basic. Finally, utilizing all the principles from the previous experiments, solid fluorene was extracted from one of the two immiscible solvents—water and methylene chloride. Part A: In part A, the solubilities of solid organic compounds were analyzed using three solvents of various polarities: water, a highly polar solvent, methyl alcohol, a medially polar solvent, and hexane, a completely nonpolar solvent. Benzophenone, a mostly nonpolar molecule with two cyclohexenanes and a polar carbonyl group, was insoluble in water, but soluble in both methyl alcohol and hexane, as shown in Table 1, because of its majorly nonpolar structure. Malonic acid, a mainly polar molecule with two polar carbonyl groups, was soluble in both water and methyl alcohol, but not in hexane, as shown in Table 1, due to its polar structure. Biphenyl, an entirely nonpolar molecule made

up of hydrocarbons, was insoluble in water, partially soluble in methyl alcohol and completely soluble in hexane, as shown in Table 1. Table 1. Observations for Solubility of Benzophenone, Malonic Acid, and Biphenyl in Various Solvents

Benzophenone

Observations Malonic Acid

Biphenyl

Water

Insoluble

Soluble

Insoluble

2

Methanol

Soluble

Soluble

Partially Soluble

3

Hexane

Soluble

Insoluble

Soluble

4

Control

N/A

N/A

N/A

Test Tube #

Solvent

1

Part B: In part B, when various alcohols were mixed with a highly polar solvent, water, and a nonpolar solvent, hexane, the two solutions mixed together completely or formed layers based on the respective polarities of each alcohol and the solvent. 1-octanol, a mostly nonpolar molecule with a single hydroxyl group and a long hydrocarbon chain, was insoluble in water but soluble in hexane, as shown in Table 2. The alcohol 1-butanol is a molecule with a relatively long hydrocarbon chain, that is shorter than the one in 1octanol, and a hydroxyl group, also was insoluble in water but soluble in hexane as shown in Table 2. Finally, methyl alcohol, a molecule with a single methyl group and a hydroxyl group, was soluble in water, but insoluble in hexane, as shown in Table 2, because it had mostly polar potentials of the hydroxyl group rather than the nonpolar potentials of the methyl group. Table 2. Solubility of Alcohols Alcohols 1-octanol 1-butanol Methyl alcohol

Solvent Water Insoluble Insoluble Soluble

Hexane Soluble Soluble Insoluble

Part C: In part C, the observed miscibility of liquid pairs also depended on the polarity of both liquids. The liquid pairs with different polarities separated into layers while the pairs with similar polarities mixed completely. Water-ethyl alcohol pair was miscible, as shown in Table 3, because of the polarity caused by the O-H bonds in both water and ethyl alcohol. Water-diethyl ether pair was immiscible, as shown in Table 3, because while water is a highly polar molecule, diethyl ether is a mostly nonpolar molecule because of the hydrocarbon chains one each side of the oxygen within its structure that is not able to from hydrogen bonds. Water-methylene chloride pair was also immiscible, as shown in Table 3, because water is a highly polar molecule while methylene chloride is only a moderately polar molecule in which the two hydrogen bonds on the central carbon partially cancels out the polarity of the C-Cl bond. Water-hexane pair was immiscible as shown on Table 3, because water is a highly polar molecule while hexane is a nonpolar molecule, entirely made up of C-H bonds. Finally, hexane-methylene chloride pair was miscible as shown in Table 3, due to the lack of polarity in hexane and the presence of slight polarity in the methylene chloride. Table 3. Miscibility of Liquid Pairs Liquid Pair

Observations

Water-Ethyl Alcohol

Miscible

Water-Diethyl Ether

Immiscible

Water-Methylene Chloride

Immiscible

Water-Hexane

Immiscible

Hexane-Methylene Chloride

Miscible

Part D: In part D, the solubilities of organic acids were analyzed in different values of pH. Benzoic acid was insoluble in water and 1.0 M HCl but was soluble in 1.0 M NaOH. Benzoic

acid was soluble in the 1.0 M NaOH because the carboxylic acid in the benzoic acid was converted into a water-soluble salt through ionization. However, with the addition of the 6.0 M HCl to the solution of 1.0 M NaOH, benzoic acid transformed back to the insoluble acid due to the lack of ionization, as shown in Table 4. On the other hand, Ethyl 4-aminobenzoate was insoluble in water and 1.0 M NaOH, but soluble in 1.0 M HCl. However, with the addition of 6.0 M NaOH to the 1.0 M HCl solution, ethyl 4-aminobenzoate became insoluble as shown in Table 4. Because amines are basic, the amino group in the structure of ethyl 4aminobenzoate makes the compound very soluble in an acidic solution. In contrary, the compound does not have acidic functional groups, which makes the compound structurally insoluble in a basic solution. Both cases implied that ionized organic acids and bases were more soluble, while un-ionized acids and bases were less soluble. Table 4. Observations for Solubility of Benzoic Acid and Ethyl 4-Aminobenzoate in Acidic and Basic Solvents Compounds

Water

Benzoic Acid

Insoluble

1.0 M NaOH

1.0 M HCl

Soluble

Ethyl 4- amino benzoate

Insoluble

Added 6.0 M HCl Insoluble Insoluble

Insoluble Soluble Added 6.0 M NaOH Insoluble

Part E: In part E, a test tube, which consisted of two immiscible liquids and a solid organic compound that was dissolved in one of the liquids, was given. While the identities of the two liquids—water and methylene chloride—and the solid compound—fluorene—were given, the relative positions of the liquids and in which liquid the solid was dissolved were unknown. First, the relative positions of the liquids were determined. Based on the densities of water and methylene chloride, methylene chloride was slightly denser than water, with the

density of 1.33 g/cm3, compared to the density of 1.00 g/cm3 in water, which placed the methylene chloride layer below the layer of water as shown in Figure 1. Then, based on the polarities of the two liquids and the solid, the liquid in which the solid was dissolved was identified. Fluorene is a nonpolar molecule, which only consists of C-H bonds. Therefore, when each layer of liquid was evaporated with nitrogen gas, fluorene was extracted from the lower, methylene chloride layer because methylene chloride is a less polar molecule than water. Although methylene chloride is moderately polar due to the higher electronegativity of chlorine compared to hydrogen, the polarity of the O-H bond in water overpowers the polarity of the C-Cl bond in methylene chloride. This experiment also reinforced the solubility principle, that solvents and solutes alike in polarity were soluble with one another while those of different polarities were insoluble.

Figure 1. Experimental Set-Up of Part E...