Recrystallization

Recrystallization

Abstract:

During this lab the process of recrystallization is used to purify 0.215 grams of potassium hydrogen tartrate (cream of tartar). A 250.00 mL beaker is filled with 150.00 mL of tap water while a 100.00 mL beaker is filled with 50.00 mL of deionized water. Both beakers are place upon a hotplate to inducing boiling. While waiting for the water to boil the solid sample of potassium hydrogen tartrate is then transferred into a test tube. Once the water reached its boiling point the test tube is suspended into the beaker. While the sample is being heated about 4.295 mL of deionized water was sporadically added to the potassium hydrogen tartrate test tube to aid the dissolving process. Once the solution reached a transparent appearance the test tube was removed from the heating apparatus and cooled in room temperature of 22.00. As the sample is cooled for seven minutes, a vacuum filtration apparatus is assembled. A test tube of deionized water is prepared and set with the potassium hydrogen tartrate test tube in an ice bath for four minutes. The potassium hydrogen tartrate test tube is then poured into the vacuum filtration apparatus. With the assistance of the chilled deionized water all particles are dispensed and impurities are washed and vacuumed out. The crystals were vacuum dried for seven minutes, squeezed in paper towel and weighed out to be 0.156 grams of recrystallized potassium hydrogen tartrate. Therefore the procedure yielded a 72.6% recovery rate of the potassium hydrogen tartrate. The crystals of potassium hydrogen tartrate are collected into two capillary tubes and placed individually into a melting station set to 260.00. The average melting point between both trials was recorded as 251.02Based on those calculations the overall experiment had a 5.99% error. [pic 1][pic 2][pic 3]

Introduction:

There are many ways to purify several different substances. This lab establishes an understanding of the purification of a solid. In order for impurities to be filtered the sample of potassium hydrogen tartrate was dissolved then allowed to recrystallize. The solution was then dispensed into a vacuum filtration apparatus in order to collect and help further purify the crystals. The crystals were dried, collected, weighed, and a percent recover rate was determined. The crystals were then distributed into capillary test tubes and set into a melting station in order to discover the experimental melting point. After collecting the proper data the average melting point and percent error were calculated. An example of recrystallization in industry would be the production of table salt. While an example for daily usage of recrystallization would be to produce fudge, rock candy, etc.

Theory:

In this experiment control throughout all procedures yields the highest recovery rate. The amount and purity of recovered material is related to temperature and crystal sizes. Allowing the solution to recrystallize in room temperatures produces larger crystals in fewer amounts. By obtaining the proper size crystals impurities are less likely to be found in the sample. The solid materials are then separated by vacuum filtration and tested for melting point average as stated in the abstract.  

Data:      

Table 1: Lewis Structure of water and potassium hydrogen tartrate[pic 4]

 [pic 5]

 Water                                                Potassium Hydrogen Tartrate (Cream of Tartar)

Table 2: Process of Recrystallization [pic 6]

    (s)        (l)  (s) [pic 8][pic 7]

Table 3: Chemical Properties

Before recrystallization:

After recrystallization:

Calculations:

% Recovery: [pic 9]

Average temperature for the experimental melting point:

Trail 1:

[pic 10]

            Trail 2:

[pic 11]

Melting point temperature average:

 [pic 12]

% Error for Melting Point: literature MP of potassium hydrogen tartrate is 267:[pic 13]

[pic 14]

Discussion:

        Error Analysis:

1. During the dissolving process about 4.295 mL of deionized water was used to help dissolve the potassium hydrogen tartrate. The procedures given had stated to use the minimal amount of deionized water so the amount used during the experiment may have diluted the sample. Therefore this mistake reduces the recovery amount and purity of the substance.  
2. During the recrystallization process the sample cooled in room temperature for 33 minutes. Due to this large crystals may have formed. Large crystals “often occlude the solvent and its dissolved impurities”(A4 158). This may therefore increase the percent error.
3. During the vacuum filtration process deionized water was chilled and used to help dispense and wash away impurities of the collected crystals. If the water was not the same temperature or cooler than the solids it may have dissolved some particles. This could decrease the amount of material recovered and increase percent error.
4.  During the melting process it was very hard to distinguish when the sample started to melt. This could affect the experimental melting point by improper data collection.

Modifications to the Procedure:

1. Abide by the procedures; use the absolute minimal amount of deionized water.
2. Watch the sample carefully as it recrystallizes to ensure proper grow of crystal size
3. Make sure all materials are prepared properly before usage during experiment.
4.  Have a consistent recorder to reduce any improper data collection.  

Conclusion: