Lab Experiment 1 - Recrystallization PDF

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Organic Chemistry I Lab Report – Recrystallization Shivam Bhavsar CHEM 2400 L01 May 16, 2020 I.

II.

Introduction Many organic compounds consist of many impurities that are gotten rid of through the process of recrystallization. The laboratory experiment done implemented this technique with the use of N-bromosuccinimide. Recrystallization is the process of purifying chemicals by dissolving the compound with some of its impurities. The precipitation formed leaves crystals behind which are purified solids. When in crystal form, they stay the same the original pure solid just in a different form. On the other hand, impure samples will have higher energy levels compared to pure samples because they are found to be less stable. This process uses the idea of when temperature is high, the solubility levels are also high. In this experiment the impure solid was placed into hot water using the hotplate. This causes the impure samples to stay dissolved, while the pure samples start to crystalize after the mixture begins to cool. The experiment done, N-bromosuccinimide was purified using the technique mentioned above (recrystallization). The solid was added to water and heated which got rid of any sort of impurity. This is because when temperature increases, so does solubility. The left-over pure substance is dried and starts to crystalize. The cooling will create crystals. The percent recovery and percent impurity of Nbromosuccinimide can be calculated when the mass of the pure crystals are found. Chemical Table Name

Structure

N-bromosuccinimide

III.

Melting Point

Density

Molecular Weight

175 °C

2.1 g/cm3

177.98 g/mol

Glassware & Set Up Filter Paper

Hot Plate

Hirsch Funnel

Ring Clamp

Glassware Thermomete Vacuum Adaptor r

Graduated Cylinder

Erlenmeyer Flask

Weigh Scale

Mel-Temp Apparatus

Ring Stand

Filter Flask

Short Stem Glass Funnel

Capillary Tube

Setup

IV.

Chemical rnx & Mechanism No chemical reaction or mechanism occurred in this laboratory experiment.

V.

Procedure

Procedures: 1. Weight 0.05 g of impure N-bromosuccinimide out and place it into the Erlenmeyer flask. 2. After, add 0.5 – 3 mL of distilled water into the flask containing the impure Nbromosuccinimide so that it can be dissolved and start boiling the content using the hot plate. 3. Let the content boil until no more solid particles are left. 4. Turn off the hot plate and allow flask to cool down until safe to grab 5. Grab another Erlenmeyer flask which contains 3 mL of distilled water and boiling chips onto the hot plate while on. Grab filter paper and place it on top of the short stem glass funnel. Place the entire funnel then onto the flask. 6. In a fast manner, filter the warm Nbromosuccinimide and add about 10% – 20% warm solvent to the warm solution. 7. Grab a beaker filled with ice and place the flask into it. If no crystals form, be sure to scrape the bottom of the flask. 8. Grab filter paper and a Hirsch funnel to form a vacuum filtration apparatus.

Observations: 1. The mass of impure Nbromosuccinimide was 0.05g. 2. Hot plate started at 70 degrees Fahrenheit until boiling point was reached. 3. Heated for five minutes until boiling point was reached 4. Flask was left out for about for few minutes to cool down to the touch. 5. Filter paper was wrapped into a cone structure to fit into the funnel. 6. Once heated the solution was poured into another flask. 7. Flask was placed into an ice bath for about 30 minutes 8. The filter flask was sealed off by place the funnel through a rubber stopper.

9. Collect crystals using vacuum filtration. 10. Collect crystals and allow them to dry. Once dry place them onto weighting paper to determine the percent recovery. 11. Calculate the percent impurity with the data given 12. Pour liquids down the sink and solid waste is thrown into laboratory trash can. Any glass ware should be cleaned and dried.

VI.

9. Waited about 10 minutes for crystals to form on the filter paper. 10. The mass of Nbromosuccinimide was found to be 0.036g. 11. The percent impurity was found to be 28% 12. Disposable glass was thrown into glass waste bin.

Calculations & Data Purifying Compounds Mass of impurified N-bromosuccinimide (g) Mass of purified N-bromosuccinimide (g) Percent recovery of N-bromosuccinimide (%) Percent impurity of N-bromosuccinimide (%)

0.05g 0.036g 72% 28%

Percent recovery: (final compound / starting weight) * 100 (0.036 / 0.05) * 100 = 72% Percent impurity: 100 – percent recovery 100 – 72 = 28% VII. Conclusion N-bromosuccinimide structure is seen to be building clock that allows and helps with the synthesis of organic molecules. In the experiment done above, N-bromosuccinimide was able to be purified and separated from the impurified solid that was given. This was done using laboratory techniques such as vacuum filtration. The N-bromosuccinimide went through recrystallization, which got rid of any sort of impurities in the solid. In this instance, water was used as a solvent so that the solute (N-bromosuccinimide) could be dissolved. With the solution being heated, it was later filtered, which allowed crystals to be formed. The percent recovery of N-bromosuccinimide was calculated to be 72%. With the recovery being about ¾ of the original amount, it is predicted that the impurity found in the solid was lower than the pure amount. Also, a decently large amount of the solute had to be purified from the impure solution. All sorts of errors could’ve occurred in the experiment that would have altered the data and calculations. One human error that could’ve occurred was not extracting all of the crystals from the filter paper. This would cause the overall mass to be significantly lower than the actual amount. VIII. Q & A 1. What is the ideal solvent for crystallization of a particular compound? What is the primary consideration in choosing a solvent for crystallizing a compound?

The ideal solvent for crystallization for a particular compound is that the solvent should be nonflammable. The solution should also not be cold, instead it being hot because the solvent will dissolve the compound. The impurities shouldn’t be dissolved so that they can be filtrated. 2. Impure benzoic acid was dissolved in hot water. The container of solution was placed in an ice-water bath instead of being allowed cooling slowly. What will be the result of cooling the solution in this manner? The end results of cooling the solution would be the production of precipitation of the benzoic acid. They would be in an impure form because of the trapped impurities. 3. What are the purposes of the following in recrystallization of solids? 1) Boiling Stones 2) Seed Crystals The point of the boiling stones in recrystallization of solids is to prevent any sort of bumping of the solution while getting boiled. On the other hand, seed crystals are used to activate crystallization if none takes place after cooling.

4. Give some reasons why suction filtration (vacuum)is to be preferred to gravity filtration. Suction filtration is preferred over gravity filtration because, suction filtration does a better job removing residue from the filter paper....