Solubility Post Lab - Lab experiment work for 322A PDF

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Lab experiment work for 322A...

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Solubility Post Lab: This week in lab, we experimented with solubility. This lab was broken down into four different parts: A, B, C, and D. In Part A, the solubility of biphenyl and succinic acid were tested in both water and hexane. For biphenyl, I predicted that it would be insoluble in water and soluble in hexane. After testing, it was clear that biphenyl was insoluble in water (we observed a hazy bottom of the tube) and soluble in hexane. Thus, my predictions were correct. This is due to the polarity of the biphenyl molecule. Biphenyl is a very non-polar molecule composed of carbon-carbon and carbon-hydrogen bonds. When placed in water, a very polar molecule, biphenyl (solute) would not be soluble in a polar solvent. However, hexane is a non-polar molecule. Therefore, when a non-polar solute (biphenyl) was placed in a non-polar solvent (hexane), biphenyl would ultimately be soluble. When testing succinic acid, I predicted that it would be soluble in water, and insoluble in hexane. Again, I was correct in my predictions after testing. This is also attributed to the polarity of the succinic acid molecule. Succinic acid is a polar molecule due to the electronegativity brough by the oxygens in the molecule. When placed in a polar solvent such as water, it was soluble. When it was placed in a non-polar solvent, such as hexane, it was insoluble. In this reaction, hydrogen bonding is possible and displayed below:

In Part B, we tested to determine if methanol and octanol were miscible or immiscible in water and hexane. For methanol, I predicted that methanol would be miscible in water and immiscible in hexane. After testing, my predictions were correct. Methanol was miscible in water due to its polarity (attributed to the hydroxide group attached), and since water is also a polar solvent, methanol would be miscible in it. However, methanol was not miscible in hexane due to hexane’s non-polar characteristics due to its extensive carbon chain. When testing octanol, I predicted that octanol would be immiscible in water and miscible in hexane. Again, I was correct

in my predictions. While octanol has a polar hydroxide group attached, the extensive carbon chain in its molecule decreases the intensity of that polarity, resulting in a non-polar molecule. Since water is polar, and octanol is not, octanol was immiscible in water as we could see in the experiment. Thus, it was miscible in hexane since the two were non-polar solvents.

Part C explored the (im)miscibility of mixing two different solvents. In the water/ethanol group, only one layer formed since ethanol is miscible in water since both are polar. The same result occurred in the water/diethyl ether since both solvents are, again, polar. Both water/ethanol and water/diethyl ether exhibit hydrogen bonding and is displayed below. When water and hexane were mixed, however, two layers formed due to the conflicting polarity characteristics of the solvents. The same layer formation occurred when water was mixed with DCM since water is polar and DCM is not. Yet, when we mixed two non-polar solvents together, hexane and DCM, they were miscible together, and therefore, only created one layer.

Water/diethyl ether

Water/ethanol

In the final part of the lab, Part D, we tested with three solutions: benzoic acid/water, benzoic acid/NaOH, and benzoic acid/DCM. In the benzoic acid/water test, we found that they were immiscible. This is because benzoic acid is non-polar due to its large benzene ring, and water is polar. The next combination we tested, benzoic acid/NaOH, was found to be miscible since NaOH reacts with benzoic acid to create benzoate ion, which is water soluble. When NaOH was added to benzoic acid, it reacted according to the following equation:

According to the equation, benzoic acid reacts with sodium hydroxide to form benzoate ion (water soluble), and since the reaction is an acid base reaction, water forms as well and an ion, in this case the sodium from sodium hydroxide. Similarly, when hydrochloric acid is added to the new developed products from the last equation, we can see reaction according to the equation:

According to the equation, when HCl is added, the proton on HCl reacts with the benzoate ion, reforming benzoic acid. With a remaining sodium ion, and chloride ion, the two ions combine into a salt, NaCl, and water remains. This followed the guidelines of acid base reaction products, so the reaction seems appropriate and accurate. The products were somewhat similar to the result of the addition of NaOH, but there were differences such as the formation of a salt, and the reformation of benzoic acid. Hypothetically, if a student were to dissolve benzoic acid with DCM, the solution would be soluble. When we tested this in trial three of Part D, this was the exact result we found. This is due to the similarities in polarities between the two molecules. However, if we added sodium hydroxide to the solution, it would deprotonate the benzoic acid molecule and turn it into an aqueous benzoate ion. The single proton would then attach to the hydroxide group on the sodium hydroxide, forming water and leaving an aqueous sodium ion. The DCM would be left unaffected, and the result would be a solution with two layers. The reaction can be described using the flowchart below:

Organic Phase

Aqueous Phase

This lab was designed to demonstrate solubility primarily in accordance with polarity. After experimenting, it was very obvious that solubility is dependent on polarity. We can clearly

conclude that “like dissolves like”; in other words, polar solvents dissolve polar solutes and nonpolar solvents are soluble in non-polar solutes. However, there are some potential errors that could have made this experiment more controlled. One thing that could be changed was the time waited after mixing the solutes and solvents. Waiting a little more time could verify that nothing separates into different layers and that everything dissolves. Also, making sure to use clean equipment with each test is important to prevent cross-contamination. Ultimately, I do believe that the purpose of the lab was achieved, as we could see how different structures of compounds affect the solubility of those compounds. This lab also demonstrated the importance of not only polarity, but intermolecular forces as well such as hydrogen bonding. Part D especially demonstrated the reasoning behind certain additions. When adding water or sodium hydroxide or hydrochloric acid, we could see how each addition affected the solutes and altered their structure to allow for solubility or formation of layers. All things considered, solubility is dependent on the polarity of the solvents and solutes and if there is a confliction between the two, multiple layers will form....