Chem 31. 1 zzz Group 2 Group Members: Cepeda, Ralph; Duhalngon, Jeia; Fabricante, Jeremias; Fajardo, Angel
Date Performed: Feb. 5, 2015 Date Submitted: Feb. 13, 2015
Experiment 2 SOLUBILITY BEHAVIOR OF ORGANIC COMPOUNDS Cepeda, Ralph; Duhalngon, Jeia; Fabricante, Jeremias; Fajardo, Angel College of Science University of the Philippines Baguio
Abstract The experiment aimed to relate relate the organic compounds’ structures structures to their solubilit solubility y and to classify classify the organic compounds as water-ether soluble (S1), water soluble (S2), strong acid (A1), weak acid (A2), base (B), neutral (N), miscellaneous neutral (M), and inert (I). The solubility of each compound was first tested in 1mL of water, and then compounds that resulted as positive or soluble were further tested in ether and those which are insoluble were tested in 5% NaOH. Compounds which are soluble in ether were classified as S1 and those that did not, as S2. Then, soluble compounds in NaOH were tested in 5% NaHCO3 and insoluble compounds with 5% HCL. Insoluble test compounds without N or S in their chemical formula were tested in concentrated H2SO4. Compounds that manifested reactions such as change in color, production of heat, formation of precipitate, or evolution of gas in the said reaction were recorded as soluble. Benzamide and aniline were insoluble to water, NaOH and HCl, but were soluble in H2SO4 and were labeled labeled as neutral neutral compounds. compounds. Benzaldehyde, Benzaldehyde, toluene, and hexane hexane are S2 or compounds compounds soluble soluble in water; Benzyl alcohol, ethanol, phenol, sucrose, and acetone on the other hand were S1 which were only soluble in water and not in ether. Benzoic acid was insoluble in water but soluble in NaOH. The experiment was successful because the solubility of all the test compounds in the given solvents were determined, observed and further classified. Based on observed reactions, acetone, ethyl alcohol and sucrose sucrose which were soluble soluble in water and ether were classified as S1 or water-ether soluble compounds. Hexane and phenol which were insoluble in water but soluble in NaOH and NaHCO3 were classified as A1 or strong acids. Benzamide which was insoluble in water and NaOH but insoluble in NaHCO3 was classified as A2 or weak acid. Benzyl alcohol, alcohol, toluene, toluene, and benzaldehyde benzaldehyde which were insoluble insoluble in water, water, NaOH and HCl but reacted reacted with H2SO4 H2SO4 were neutral; aniline was a miscellaneous neutral compound because it did not react to any of the test solvents; while benzoic acid is inert because it was not dissolved in the solvents.
Introduction One important property that organic compounds exhibit is that their structure is related to their solubility. Solubility is the amount of a substance that will dissolve in a given amount of another substance and is typically expressed as the number of parts by weight dissolved by 100 parts of solvent at a specified temperature and pressure or as percent by weight or by volume. The general rule used in determining whether a solute is soluble or insoluble in a given solvent is “like dissolves like” where nonpolar solutes dissolve in nonpolar solvents; polar solutes dissolve in polar solvents or chemical reactions may occur between the solvent and the solute causing dissolution. Compounds that are branch-chained are more soluble than the corresponding straight-chained compound. Branching lowers intermolecular forces and decreases intermolecular attraction. The position of the functional group in the carbon chain also affects solubility. The solubility of organic organic compounds compounds in organic organic solvents solvents should be determine determined d in order to plan for a variety of laboratory operations which include choosing solvents for organic reactions, dissolving substrates
for spectral analyses, cleaning glassware, extraction, thin layer and other chromatography and crystallization. Knowledge of the solubility of organic compounds is essential tool to a budding chemist. In designing industrial processes such as crystallization and liquid extraction process, an understanding of the solubility behavior of different chemicals is essential in selecting an appropriate solvent (Jiangang et al, 2014). In this experiment, the different solubility behaviors of organic compounds were examined. The obtained results have pave way for the classification of compounds. Each test has allowed students to classify the organic compound as either soluble or insoluble in each of the test solvents. Test organic compounds that are hydrocarbons such as toluene were insoluble in water. This is because of their non polar nature. In addition, if there is a polar functional group in a certain compound such as in the case of benzaldehyde, it is slightly soluble in water. In general, the results cemented the concept of “like dissolves like”. As observed in the experiment, polar substances such acetone is readily miscible with water. In contrast, non polar molecules such as hexane are insoluble with water. Consequently, the experiment shed light on the intermolecular forces governing attraction between and among molecules. This is best exhibited by sucrose, a partially polar substance yet it was dissolved in water due to the stronger solvent-solute bonding formation compared to the solvent-solvent or solute-solute molecular interactions. The objectives of the experiment were to relate the organic compounds’ structures to their solubility and to classify the organic compounds as water soluble (S1), ether soluble (S2), strong acid (A1), weak acid (A2), base (B), neutral (N), miscellaneous neutral (M), and inert (I).
Results and Discussion Hexane Hexane is a non-polar compound that’s why it is insoluble in water which is a polar solvent. A non-polar compound is hard to dissolve because of the presence of H-bonding. The dissolution of hexane is following the “like dissolves like” principle because NaOH is a strong base thus dissolving hexane which is a strong acid. Hexane also dissolved in NaHCO3 because it is a strong acid forming water-soluble salts. Benzamide All non-polar compounds are insoluble in water, this is the reason why benzamide did not dissolve in water thus dissolving it in NaOH. NaOH is a strong base that ionizes weak acids whereas benzamide is a weak acid. NaHCO3 is added to benzamide because it is soluble in NaOH. Less acidic compounds do not dissolve in NaHCO3 therefore there is no formation of water soluble salts. Acetone Acetone is the most common ketone thus it’s a polar compound. Following the principle “like dissolves like”, water (a polar compound) dissolves acetone. Compound that dissolves in water also dissolves in NaOH, NaCHO3, HCl, and H2SO4 because all these are primarily water. Ethyl alcohol Six drops of ethyl alcohol was mixed with one millilitre of water. The resulting solution was a clear liquid solution. The physical description implies that ethyl alcohol is miscible in water. The result also tells us that ethyl alcohol must have a polar bond since water is a polar compound .
Ethanol is a compound with non-polar and polar bonds. Ethanol’s formula looks like this: CH3CH2OH. The bonds between the carbons are non-polar, while the bond of the OH group of the compound is polar . The strength of the attraction of the OH group makes it completely miscible in water (Solubility of Things, n.d.). After being determined as water soluble, ethyl alcohol’s solubility was tested using ether as a solvent. Ethyl alcohol was also dissolved in the mixture. The result of the experiment suggests that ethyl alcohol is also ether soluble. Ethers are slightly polar, which explains the dissolving of the ethyl alcohol . Ethers, Diethyl ether for example, are also non-polar compounds used to determine if a water-soluble compound is extremely polar. A substance cannot be dissolved in ether if it is . But since ethyl alcohol was dissolved, it is not extremely polar. Benzyl alcohol When benzyl alcohol was mixed with water, the resulting mixture had two layers. This means that benzyl alcohol was not soluble in water despite being an alcohol. Being an alcohol, benzyl alcohol is a polar compound. Alcohols with one to three carbons are completely miscible in water, but the solubility of the alcohol decreases as the number of carbon increases . Benzyl alcohol contains seven carbon atoms which makes it partially soluble in water. Two common functional groups dissolve in sodium hydroxide, which are carboxylic acids and phenols (University of Puget Sound, n.d.). Benzyl alcohol is neither of the two explaining why it did not dissolve in NaOH. The 5% HCl solution was unable to dissolve the benzyl alcohol because HCl dissolves basic compounds unlike benzyl alcohol which has a slight acidic property. Concentrated sulfuric acid is quickly able to dissolve benzyl alcohol. The resulting solution had change in color, release of heat and formation of precipitate. Sulfuric acid protonates compounds containing oxygen. Sulfuric acid was used to test whether a compound without nitrogen or sulphur is a neutral compound or an extremely weak base . Aniline Similarly to the benzyl alcohol, amides like aniline are soluble to water, but, since aniline has six carbons, its solubility in water decreases . Also like benzyl alcohol, aniline is not a phenol or a carboxylic acid. Hence, there was no reaction with sodium hydroxide (University of Puget Sound). Since aniline contains nitrogen, it was not tested with sulfuric acid and was classified as a miscellaneous neutral compound. Sucrose is soluble in water because the bond formation between the solvent-solute interactions is strong enough to disrupt the weak bonds between individual molecules of sucrose and the hydrogen bond in water. This is also because water is a polar solvent and sucrose is partially polar molecule. As such, the rule of the thumb that “like dissolves like” clearly applies here. Likewise, sucrose has been slightly soluble in ether because of the slight polarity of the latter. Polarity of the ether is due to the electro negativity difference between its oxygen and carbon atoms. Hence, sucrose could be classified as water-ether –soluble compound. On the other hand, toluene is immiscible to water due to the fact that they are non polar and polar, respectively. The same principle applies when toluene is subjected to 5% NaOH. As a polar molecule, sodium hydroxide does not react with non polar molecules. However, when subjected under concentrated sulfuric acid, the toluene reacts by changing its color. The mechanism behind this is that sulfuric acid interacts with toluene through electrophilic aromatic substitution. Electrophilic Aromatic Substitution (EAS) is a “substitution reaction usually involving the benzene ring; more specifically it is “a reaction in which the
hydrogen atom of an aromatic ring is replaced as a consequence of electrophilic attack on the aromatic ring”. As in the case of toluene, its benzene ring was attacked by the electron-rich sulfuric acid. That’s why, miscibility occurred between the two compounds and toluene is classified as neutral compound. In terms of the solubility of benzaldehyde, it is sparingly soluble in water. Despite the non polarity behavior of its benzene ring, an addition of the aldehyde functional group makes benzaldehyde slightly polar. Thus, there is a minimal solubility in the said compounds. In the case of benzaldehyde’s solubility with ether, it is almost homogenous. This is because the large hydrophobic aromatic ring of benzaldehyde could readily react with non polar solvent such as ether. Benzoic acid solubility The primary reason benzoic acid is only slightly, barely or not at all soluble in cold or room temperature water is that, even though the carboxylic acid group is polar, the bulk of the benzoic acid molecule is non-polar (water is polar). It is only the carboxylic group that is polar. Also, carboxylic acids such as benzoic acid are relatively weak acids, and thus exist mostly in the acidic (protonated) form when added to pure water. However, ionization, increase in pH, or increase in temperature increases the solubility of the benzoic acid molecule in water. The explanation behind this is that the hydrogen-bonding, hydrophilic effect of the carboxylic acid group is not powerful enough to overcome the larger hydrophobic effect of the 6-carbon benzene group on benzoic acid. Phenol Phenols show acidic nature and hence are soluble in alkalies like NaOH, Na 2CO3 etc. The acidic nature is due to formation of resonance stabilized phenoxide ion formed by losing a proton from -OH group. Phenol is also soluble in water to some extent, although it did not dissolve during the experiment. It is due to its ability to form hydrogen bonding with water molecules. However the large part of phenol molecule is phenyl group that is non polar and hence its solubility if limited in water. When alkalies are added to phenol, the above equilibrium is shifted more to the right side as the H + ions are removed by the OH- ions that are furnished by alkalies. Thus more and more phenol is converted to phenoxide ion that is soluble in water. NaHCO3 is not a strong alkali and hence it cannot provide as much OH - ions that are required to shift the above mentioned equilibrium. Hence only small amount of phenoxide is formed. Hence phenol is sparingly soluble in NaHCO3.
Summary and Conclusion Based on the data gathered and observations made, the students classified hexane and phenol, which were insoluble in water, but soluble in NaOH and NaHCO3 as strong acids (A1). Ethyl alcohol, acetone and sucrose were classified as water-ether soluble compounds (S1). Then, benzamide was classified as a weak acid (A2) after it was found out to be insoluble in water and NaHCO3 but soluble in NaOH. Aniline and benzoic acid were classified as a miscellaneous neutral compound and an inert compound respectively after not showing solubility in any of the solvents. Benzyl alcohol, toluene and benzaldehyde which were insoluble in water, NaOH and HCl but showed signs of chemical reaction with H2So4 were classified as neutral compounds (N).
ANSWERS TO QUESTIONS 1.
2.
What are the types of intermolecular forces present in solutions formed due to solvent-solute interactions? Based on the results of the experiment, only three organic test compounds (sucrose, acetone and ethyl alcohol) were soluble in water. It implies that the hydrogen bonding in the water molecules and the dipole-dipole interactions among the polar solute molecules were replaced by hydrogen bonding between the solute and the solvent. These three were also dissolved in ether making the test compounds non-polar since ether is a non-polar compound. Ether was able to dissolve acetone and ethyl alcohol by London Dispersion Force. Dispersion forces exist between all kinds of molecules due to the movement of electrons within the molecule,creating a momentary dipole. Water is a polar molecule with oxygen carrying a partial negative charge and hydrogen with a partial positive charge, thus exhibits dipole-dipole forces. In addition, the O-H bond in the molecule allows hydrogen bonding between the molecules. Therefore, for aqueous solutions of sucrose, ethyl alcohol and acetone which are all polar molecules, the predominant intermolecular forces are dipole-dipole forces, hydrogen bonding and dispersion forces.On the other hand, diethyl ether is essentially a non-polar solvent and can only dissolve non-polar substances.Dipole-dipole forces cannot exist between non-polar molecules because of the lack of a dipole in its structure,hence the only significant intermolecular forces between non-polar molecules, such as those in ether solutions of ethyl alcohol and acetone, are dispersion forces. To sum it up: Acetone-H2O --London dispersion, dipole-dipole, H-bonding Ethyl alcohol-H2O --London dispersion, dipole-dipole, H-bonding Sucrose-H2O --London dispersion, dipole-dipole, H-bonding Acetone-Ether --London dispersion Ethyl alcohol-Ether --London dispersion Write the balanced chemical equations of the solvent-solute combinations that formed solutions due to chemical reactions.
3.
On the basis of solubility behavior, show how each of the following pairs of compounds may be distinguished from each other. a. CH ₃ NHCH ₃ and CH ₃ (CH ₂ ) ₅ CH ₂ NH₂ CH3NH2 is a small, polar molecule, that can hydrogen bond with H2O. CH3(CH2)5CH2NH2 is also capable of hydrogen bonding with H2O through the amino groups but is lesser polar because of the presence of a much longer, non-polar, hydrocarbon chain.
b. Ethanal and hydroxyethanal CH3CHO is a small, polar molecule, that can also hydrogen bond with H2O through the O on the C=O group. HOCH2CH is also small, polar, and can also hydrogen bond with H2O through –OH group in addition to hydrogen bonding with H2O through the O on the C=O group. c. Benzyl amine and benzyl alcohol The compounds that contain the large, non-polar, benzene rings are not that very soluble in H2O. Amines and alcohols are both capable of forming hydrogen bonds with H2O, but alcohols have the stronger hydrogen bonding. Also, benzyl amine is soluble in HCl but benzyl alcohol is insoluble.
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