Acid base extraction - kkkmk PDF

Preview

Summary

kkkmk...

Description

Organic chemistry lab- TA Maria Ballivian

Acid base extraction: separation of an organic acid, a base and a neutral compound. Patricia Archambault

Introduction In chemistry, an extraction is an important technique to remove a specific compound from a mixture. When an extraction takes place, that means that in that mixture is an unequal mixture of solute between multiple immiscible solvents. 1 Immiscibility of the solvents in the solute is important for the success of the extraction. When the solvents are immiscible, it means that they will not mix, therefore creating layers made of each solvent. 1 If the solvents were not immiscible, they would mix and you would not get the solid precipitated outcome from each chemical that is expected from an extraction. The solvents used in an extraction are important. These solvents must meet certain requirements. These requirements include at least one component of the mixture must be fully dissolved in the solute, the reaction needs to be stable and cannot be reversed, and temperatures and pH’s of the compound must be closely monitored.2 One of the most important and widely used methods of extractions in organic chemistry is the Acid-base extraction. During an Acid base extraction, a mixture of acid and base are separated to present both the acid and the base in a solid form, isolated from one another. 2 For an acid base extraction, you will need an acid, a base, and a neutral compound. Through the process of the extraction, these compounds will form precipitates and be separated. 3 The components of the mixture is what coins the name acid base reaction, since it is comprised of the acid, and the base and they are being extracted from one another.

The solubility properties of each compound in an extraction are extremely important to consider. In an acid base extraction, note that when an acid and a base react together, they will form a salt. This salt, in this specific experiment, will be formed from Benzoic acid, the acid and

4 Chloranoline, the organic base. With the formation of this salt, Naphthalene which is the neutral compound is left alone in the organic layer. 1The layers created will be separated from one another, and the melting points of each will be determined. The mass and the melting points will help determine the accuracy of the extraction. Mass will play a role in calculating the percent recovery, which is expected to be 100% assuming all the compounds were successfully and fully separated. The melting points of each precipitated compound should be the same as the expected/ literature values for melting points. If they vary, the purity of the compound should be considered. If the melting point range is broad, it is a strong sign that impurities exist, since impurities can cause wider temperature ranges. 4

Experimental section In a 125ml Erlenmeyer flask, transfer 3g of the benzoic acid, 4chloroaniline and naphthalene mixture.

Remove the bottom layer from the funnel, and place into a 125ml Erlenmeyer flask. Label as flask #1.

Replace separatory funnel into the iron ringdroplets and put to the Add 6M HCl stopper in place. flask #2, checking with Add 3M in drops, pH paper to ensure the checking with pH solution is acidic. to be sure your Collectpaper the precipitate solution is basic. by vacuum filtration. Now 4-chloranoline

In the mixture, add 30ml of diethyl ether.

Transfer the mixture to a 125ml separatory funnel. Use approximately 20 ml of fresh ether to aid the transfer as needed.

Unscrew the cap slightly to allow ventilation.

To this mixture, add 30ml of 5% HCl. Cap the funnel, and gently shake.

Remove theflask aqueous Cool the in ice layerforin10-15 the separatory minutes. funnel into an Erlenmeyer flask (flask #2)

Now the separatory Collect funnel in the the iron precipitate by ring contains vacuum filtration. benzoic acid and Place the precipitate naphthalene (which between 2 filter is ether solution) papers it to Add for 50ml ofdry. 50% NaOH to the ether solution. Cap and Add anhydrous sodium sulfate shake. in order to dry the ether layer. Allow the precipitate to set for several minutes.

Rinse the precipitate with cool water, and dry. This precipitate is solid benzoic acid.

Evaporate ether using a vacuum pump, until precipitate forms. Weigh the solid. Measure the melting point for each solid.

Now the separatory funnel only has naphthalene. To this funnel, add 20ml of saturated sodium chloride.

Filter the drying agent into a tared 125ml vacuum flask. Rinse the drying agent with fresh diethyl ether and add to vacuum flask.

Discard the bottom layer of the separatory funnel into aqueous waste. Drain the ether layer into a 125ml flask (flask #3)

Add enough anhydrous sodium sulfate to dry the ether layer. Allow to set for several minutes

Table of chemicals Table 1: Chemicals used, with their physical and chemical properties Sodium hydroxide Formula

NaOH

Diethyl ether (C 2 H 5 )2 O

Benzoic acid

4chloroaniline

C7 H 6 O2

C6 H 6 CIN

White crystalline solid

Pale yellow solid

Naphthalene

C 10 H 8

Hydrochlori c acid HCl

Anhydrou s sodium sulfate Na2 S O 4

Structure

Physical propertie s

white crystalline solid.

Colorless

Odorless -116.30℃

Bp: 1388℃ Molar mass: 40g/mol

Chemical propertie s

Corrosive Water soluble

Colorless

Mp: -114.4℃

Bp: 34.60℃

Mp: 122℃

Molar mass: 74.12 g/mol

Bp: 249.20℃

Flammabl e

White crystalline solid

Sweet odor

Mp: Mp 122℃

White crystalline powder

Mp: 68-71℃

Bp: 232℃

Mp: 888℃

Mp: 80℃ Bp: -85.05℃

Bp: 1100℃

Molar mass: 36.46g/mol

Molar Mass: 142.06 g.mol

Corrosive

Bp: 218℃

Molar mass: Molar mass: 122.12g/mo 127.57 g/mol l Corrosive Toxic

Irritant

Irritant

Irritant

Irritant

Health hazard

Corrosive

Health hazard

Health hazard

Environmenta l hazard

Acute toxic

Slightly water soluble

Environmenta l hazard

Molar mass: 128.17 g/mol

Irritant

Water insoluble

Irritant

Results Table 2: results with mass, boiling point and percent recovery. 4-chloraniline

Benzoic acid

Naphthalene

Mass

.902g

.870g

.729g

Melting point

68℃-70℃

120℃-122℃

80℃-84℃

Percent recovery

90.2%

87%

72.9%

Percent recovery calculations Amount of pure productrecovered Amount of crudematerial used 4-chloraniline:

.902 g x 100=90.2 % 1g

Benzoic Acid:

.870 g x 100=87 % 1g

Naphthalene:

.729 g x 100=72.9 % 1g

x 100

Discussion Through the course of the experiment, 3 chemicals were extracted from a mixture. This mixture contained 3g of seemingly equal parts of 4-chloranoline, benzoic acid and naphthalene. Since it was equal parts, that means there should have been 1g of each chemical in the mixture. The results in table 2 however, do not demonstrate the results expected if there was truly 1g of each chemical recovered. If the full 1g was recovered, then the percent recoveries would be 100%. Though they are not off as shown in table 2, they are also not completely correct. If the mixture truly contained equal parts, then some of the chemicals were lost in the extraction. One of the largest causes of this loss could be resulted by the number of transfers present in this experiment. As outlined in the experiment, chemicals were moved to and from funnels, flasks and filter papers. During this process, some of the chemicals could have been lost. Filter paper is designed to separate solids from liquids. In this process, the filtration paper has a chance to soak up some of the liquid, which can change the amount of solid precipitate formed. Another reason the percent recovery could have been lost is simply that equal parts of the chemicals were not placed in the mixture. It is assumed there is 1g of each, but some substance could have been lost in the transfer process to the initial mixture. If you compare the melting points given in table 1, which are the theoretical values, with the melting points given in table 2, you can see that they vary. The literature value for the melting point of benzoic acid is 122 ℃ . The measured melting point in the experiment was 120 ℃−¿ 122 ℃ . Though the literature value lies within the range of the recorded values, it is on the higher end. Since we know that impurities can decrease your melting point, it is safe

to assume the precipitate of benzoic acid did not contain any impurities. In fact, the higher-thanaverage melting point could be signs of something else. These could include heating the solid too fast, or an imprecise thermometer. Since the recorded temperature was just slightly higher than expected, the precipitate of Benzoic Acid could have been heated slightly more rapidly than it should have been, which will cause overheating making the temperature rise too rapidly. Likewise, the apparatus of heating could have been inaccurate ever so slightly. An addition reason for the varying melting points could be the result of chemicals mixing. Since the percent recoveries of the chemicals were lower than expected, there is a possibility that some of the chemicals during the extraction could have accidently been mixed or exposed to one another. In other words, the precipitate of a chemical, for instance Benzoic acid, would have traces of another chemical, such as 4-Chloroaniline. The same argument for Benzoic acid can be made for 4-chloranoline, as the measured melting point was slightly higher than the range of the literature values. For Naphthalene however, the recorded value for the melting point was on the lower end of the literature values. Since the percent of recovery of Naphthalene was the lowest, it is a probable assumption that since the mass of the chemical was much lower than what it should have been, this could have had a negative affect on the melting point recorded, causing it to be lower. Knowing that impurities will lower the boiling point of a chemical, it is also possible that the precipitate of Naphthalene contained impurities.

Conclusion

The theories behind the extractions were demonstrated within the experiment. The results from table 2 represent the presence of impurities. As discussed in the introduction, impurities will

broaden the range of the melting point from the literature values. For the compounds 4chloranoline and Benzoic acid tested in the experiment, the expected values and the recorded values for the melting points varied, suggesting the presence of impurities. Naphthalene demonstrated minimal evidence of impurities, as the recorded temperature did not vary much from the literature value. The required characteristic of immiscibility in the compounds was also demonstrated. Since the precipitate formed in layers, which contained each compound, the mixture was immiscible and could be separated into portions. Though the percent recoveries were not 100%, they help aid in the theories provided. Impurities can be accounted for, to explain the varying melting point values. This shows that extractions are tedious and important processes, as sometimes compounds are not fully separated even if they are immiscible. The process of an acid base extraction demonstrated in this experiment can be used in everyday situations. One example of an acid base extraction in a real-life situation is the extraction of phosphorus from soil. 5 Phosphorus is an important component in soil health. Being able to extract the phosphorus to measure the amount of the compound is critical to understanding the health of the soil. The more phosphorus, the healthier the soil. Without acid base extraction, it would be difficult to tell the health of soil on a chemical level, which is important for growing crops, trees, etc.

Citations 1) Weldegirma, S. Experimental Organic Chemistry, 9th ed.; University of South Florida: Tampa, 2021.

2) What is solvent extraction and Why is it important? (2010, July 13). Retrieved February 04, 2021, from https://sciencestruck.com/solvent-extraction#:~:text=Two%20immiscible %20liquids%20are%20shaken%20with%20the%20mixture.,cost-effectiveness%2C%20it %20is%20widely%20used%20in%20various%20sectors. 3) Nalli, T., Dr. (n.d.). Chem 350 Expt #2 - ACID/BASE extraction - fall 2016. Retrieved February 04, 2021, from http://course1.winona.edu/tnalli/f16/expt2%20acid%20base %20extraction.html 4) Libretexts. (2020, July 14). 5.3: Melting POINT analysis- identity and purity. Retrieved February 04, 2021, from https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Book %3A_How_to_be_a_Successful_Organic_Chemist_(Sandtorv)/05%3A_HOW_TO_INTE RPRET_YOUR_RESULTS/5.03%3A_MELTING_POINT_ANALYSIS_IDENTITY_AND_PURITY

5) Benjamin L. Turner, Barbara J. Cade-Menun, Leo M. Condron, Susan Newman, Extraction of soil organic phosphorus, Talanta, Volume 66, Issue 2, 2005,Pages 294-306,ISSN 0039-9140, (https://www.sciencedirect.com/science/article/pii/S0039914004006733)...