Date Performed: 30 Performed: 30 Jan 2017
Deseo, Ma. Rogemae
Date Submitted: 09 Submitted: 09 Feb 2017
Gerolaga, Winston Jake Group:
Experiment No. 1 Solubility Behavior of Organic Compounds
The strength of a compound’s intermolecular intermolecular forces determines many of its physical properties, including its boiling point, melting point, and solubility. Solubility is the extent to which a compound, called the solute, dissolves in a liquid, called the solvent. Compounds dissolve in solvents having similar kinds of intermolecular forces (Smith, 2011). The compound’s nature or polarity hugely affects its solubility as well as the temperature, molecular weight, acidity or basicity of the compound, intermolecular forces of attraction, structure of the compound, and pressure. Generally, this experiment aims to test the solubility of representative organic compounds in different solvents. Specifically, this aims to classify the given compounds into different solubility classes. This also aims to relate the solubility of an organic compound with its structure.
In this experiment, the procedures from the laboratory manual were all followed. The solubility of the organic compound samples were determined using different solvents. Acetone, benzoic acid, phenol, aniline, benzamide, tert-butyl chloride, benzyl alcohol, ethyl alcohol, toluene, benzaldehyde hexane, and sucrose were the organic
compounds used in this experiment. Additionally, the solvents used in this experiment are distilled water, 5% NaOH, ether, 5% HCl, 5% NaHCO 3 and concentrated H 2SO4. Five drops of distilled water, the first solvent used, was placed into twelve test tubes. For each of the test compounds, 1-2 drops or a pinch was added into one of the test tubes. Samples were shaken vigorously and recorded as soluble or insoluble. For water-soluble compounds, required amount of the fresh sample into 5 drops of ether were added to check if the compounds were also ether-soluble. Ether-soluble compound belong to S1 group, and ether-insoluble compounds belong to S2 group. The solubility of water-insoluble compounds were tested first using 5% sodium hydroxide (NaOH) solution. For NaOH-soluble compounds, solubility with 5% sodium bicarbonate (NaHCO 3) solution was also tested using a fresh sample of the compound. NaHCO3-soluble compounds were classified as A1, and NaHCO 3-insoluble compounds were classified as A2. For NaOH-insoluble compounds, solubility with 5% hydrochloric acid (HCl) solution was tested using a fresh sample compound. Basic compounds (B) were insoluble in 5% HCl; miscellaneous neutral compound (M) were insoluble in HCl and contains N or S. The solubility in concentrated sulfuric acid (H 2SO4) of the compounds that did not contain N or S were determined, and classified as inert compound (I) for H2SO4-insoluble compounds and neutral compound (N) for H 2SO4-soluble compounds.
Results and Discussion Solubility tests are essential to determine the functional group of an organic
compound. In this experiment; however, the relationship of the solubility of the known compound from a certain functional group with its structure and chemical properties are focused.
Basically, the energy needed to break up the interactions between the molecules or ions of the solute comes from new interactions between the solute and the solvent. Structures of molecules can affect their solubility. Solubility of different samples were classified based on the observations made on the mixtures. Acetone, ethyl alcohol, hexane, tert-butyl chloride, and sucrose are all soluble in water and ether ( Table 1). 1). Most of them contain less than four carbons and some polar groups of oxygen which increased their solubility. Toluene is soluble only in 5% hydrochloric acid, therefore it was classified as a basic compound. Phenol, a weak acid, is only soluble in 5% sodium hydroxide hence it belongs to the NaHCO 3-insoluble classification (A2). Aniline Aniline and benzamide, benzamide, although slightly soluble, were considered as miscellaneous neutral compounds since they remained insoluble in 5% hydrochloric acid. In the case of aniline, the presence of nitrogen reduced the basicity of the compound affecting the protonation and solubility. However, benzamide can also be considered as a basic compound just like toluene because it slightly dissolved in 5% hydrochloric acid. Benzoic acid is soluble in concentrated sulfuric acid, therefore it is a neutral compound. Finally, benzaldehyde and benzyl alcohol are both inert compounds because the two substances remained insoluble in concentrated sulfuric acid. Uniformity in the solution and absence of precipitates, colloidal suspensions and, separations or the formation of layers were observed in soluble compounds. Presence of precipitate and fluid separation indicated insolubility. According to Smith (2011), (2011), most ionic compounds compounds are soluble in water, water, but are insoluble in organic solvents. If an organic compound contains one polar functional capable of hydrogen bonding with the solvent for every five C atoms it contains, it is considered as water-soluble only. Water-soluble organic compound has an O- or N-containing functional group that solubilizes its nonpolar carbon backbone. The presence of a polyfunctional group is indicated by a partially soluble sample, since hydrocarbons are insoluble in water. The solubility in 5% sodium hydroxide solution of a water insoluble sample is a strong indication of an acidic functional group. Deductions about molecular size and composition can also sometimes be made.
Members with fewer than about five carbon atoms are water soluble, whereas the higher homologs are insoluble, in cases of homologous series of monofunctional monofunctional compounds. The solvents involved in the experiment have distinct properties from one another. Water is a polar solvent which dissolves polar compounds. Diethyl ether is a nonpolar solvent which is used to determine whether the water-soluble substance is extremely polar. Compounds dissolve in aqueous base solutions because they form sodium salts that are soluble in aqueous medium. Furthermore, these compounds’ solubility in sodium bicarbonate, which is less basic than sodium hydroxide differentiates strong acids from weak acids. Basic compounds like aliphatic amines readily dissolve in acid because they form hydrochloride salts that are soluble in aqueous medium. Concentrated sulfuric acid protonates all organic compounds that contain oxygen and/or nitrogen, as well as alkenes and a few aromatic hydrocarbons. These protonated compounds are then dissolved because sulfuric acid is a highly polar liquid. The dissolution of compounds in H 2SO4 can produce large amounts of heat and/or a change in the color of the solution. Based on the observations made, benzaldehyde, turned into a dark orange H 2SO4 -soluble solution. Benzoic acid was partially dissolved. Benzyl alcohol, on the other hand, formed a cloudy light orange H 2SO4-insoluble solution.
Benzyl alcohol (C6H5CH2O
Neutral Compound (N) H2SO4 -
Benzoic acid (C6H5COOH
soluble Neutral Compound (N)
(C7H7NO) Ethyl alcohol Soluble
(C2H5OH) Hexane (C6H14)
Soluble Compound (B) Ether-soluble (S1) Ether-soluble (S1)
(C6H5OH) Tert-butyl chloride
Basic Compound (B)
Table 1. 1. Solubility classes of the samples.
Conclusion and Recommendations
Therefore, the nature of the solvent affects the solubility behavior of the sample. The structural formula of the sample has also a significant effect to its solubility. The presence or absence of functional groups of which the compound belongs to can be determined based on the solubility of the compound in the water, dilute acid, or dilute base. Moreover, the structure and polarity of organic compounds are important in determining the solubility and that solubility is a vital thing to know when handling organic compounds. Some observations did not match the expected outcomes based on the existing theories and past experiments. The inconsistencies might be due to the excessive additions of samples or the mixtures were not shaken thoroughly. In addition, the verdicts for the solubility of the mixtures could be influenced by erroneous assessment done by the researchers.
Cepeda, R., et.al. (2015, April 2). Solubility Behavior of Organic Compounds. Retrieved from https://www.scribd.com/document/260697271/Solubility-Behavior-of-Organic-Co mpounds Miranda M. & Ogario, J.P. (2014, July 31). Preliminary Tests and Solubility Classification of
https://www.academia.edu/10879682/Preliminary_Tests_and_Solubility_Classific ation_of_Organic_Compounds Smith J.G. (2011). Organic Chemistry (3rd Ed.). (3rd Ed.). The McGraw-Hill Companies, Inc., 1221 Avenue of the Americas, New York, York, NY 10020.