Chapter 5: Recrystallization of Benzoic Acid & Melting Point of Benzoic AcidJoseph PersonelliLab Partners: Dominic Gonzalez & Benjamin LowryChemistry 2400Instructor: Joseph KappelLaboratory Assistant: Stacey MendigutiaJanuary 13, 2015

Results:

i. Structures:

Pure Benzoic AcidMehtanol

ii. Measured/Collected Data:

Trial 1Pure Benzoic Acid& H2OTrial 2Impure Benzoic Acid & H2OTrial 3Impure Benzoic Acid, H2O & Methanol

Filter Paper (g)0.106 g0.107 g0.103 g

Benzoic Acid (g)0.0600 g0.0600 g0.0604 g

Table 1: This table shows weights of the filter paper and the added benzoic acid

Trial 1Pure Benzoic Acid& H2OTrial 2Impure Benzoic Acid & H2OTrial 3Impure Benzoic Acid, H2O & Methanol

Mass of Filter paper after drying (1st )0.151 (g)0.118 (g)0.122 (g)

(2nd )0.135 (g)0.116 (g)0.119 (g)

(3rd )0.130 (g)0.115 (g)0.119 (g)

Final mass of Filter Paper0.130 (g)0.115 (g)0.119 (g)

Table 2: This table shows the weight of the filter paper with dried benzoic acid.

Starting to melt (C)Completely Liquefied(C)

Pure Benzoic Acid105 (C)122 (C)

Impure Benzoic Acid100 (C)115 (C)

Trial 1 Product105 (C)114 (C)

Trial 2 Product 106 (C)114 (C)

Trial 3 Product95 (C)110 (C)

Table 3: This table shows the temperature that each substance started to melt and when each substance became completely liquefied

iii. Calculated Results:

Melting Point

Pure Benzoic Acid7 (C)

Impure Benzoic Acid15 (C)

Trial 1 Product9 (C)

Trial 2 Product 8 (C)

Trial 3 Product15 (C)

Table 4: The calculated melting points of each substance

Trial 1Pure Benzoic Acid& H2OTrial 2Impure Benzoic Acid & H2OTrial 3Impure Benzoic Acid, H2O & Methanol

Mass of dried benzoic acid (g)0.024 (g)0.008 (g)0.016 (g)

Table 5: Mass of the dried benzoic acid that was left on the filter paper

Percent Yield

Trial 1Pure Benzoic Acid& H2O40 %

Trial 2Impure Benzoic Acid & H2O13%

Trial 3Impure Benzoic Acid, H2O & Methanol26.5%

Table 6: The calculated percent yield for trial 1, trial 2, and trial 3

iv. Calculations:

Mass of dried benzoic acid = final mass of dried filter paper filter paper

Trial 1: 0.130(g) 0.106(g) = 0.024 (g) Trial 2: 0.115(g) 0.107(g) = 0.008 (g) Trial 3: 0.119(g) 0.103(g) = 0.016 (g)

Melting Point = Temperature substance becomes completely liquefied temperature substance initially starts to melt

Pure Benzoic Acid: 122 (C) 105 (C) = 17 (C) Impure Benzoic Acid: 115 (C) 100 (C) = 15 (C) Trial 1 Product: 114 (C) 105 (C) = 9 (C) Trial 2 Product: 114 (C) 106 (C) = 8 (C) Trial 3 Product: 110 (C) 95 (C) = 15 (C)

Percent Yield = (mass of dried benzoic acid / mass of initial benzoic acid)* 100

Trial 1 Product: (0.024 / 0.0600) * 100 = 40 % Trial 2 Product: (0.008 / 0.0600) * 100 = 13 % Trial 3 Product: (0.016 / 0.0604) * 100 = 26.5%

v. Discussion:

The purpose of this experiment was to dissolve pure benzoic acid and impure benzoic acid and recrystallize it to get a new product of pure benzoic acid. A purification technique was used to purify the impure benzoic acid. Dissolving the impure benzoic acid in warm water and in one trial warm water and methanol did this. The idea behind this was that the impurities would remain in the water solutions and the benzoic acid would recrystallize together when it was quickly cooled by being placed in a beaker of ice water. Pure benzoic acid has a melting point of 122 C. The trial 1 product, pure benzoic acid and water, had a melting point of 115 C. In theory, trial 1 should have a very close melting point that of pure benzoic acid. Because there was a 17C change in the melting point this could indicate some impurities in the water. The trial 1 product of pure benzoic acid had a percent yield of 40% of the original weight of the pure benzoic acid that was added. This percent yield was relatively higher when compared to the percent yield of trial 2 product and trial 3 product of 13% and 26.5% respectively. One possible reason for such a low percent yield even for the trial 1 product is that some of the product could have missed the filter paper in the vacuum filter apparatus and fell into the catch flask. To eradicate this from happening again, larger pieces of filter paper could be used to line the apparatus to catch all of the recrystallized benzoic acid.

vi. Questions:

5-26: After isolating 45 mg of purified substance it can be calculated that 75% of the substance was recovered. After receiving an addition of 8mg from the mother substance there is an 88% percent total recovery.

6-5: Filter paper is a poor choice of surface to powder or crush a solid crystalline sample before placing it into a capillary melting-point tube because the crushing of the sample with the tube could cause the paper to mix into the powder. This could result in a change of melting point if bits of the filter paper get mixed into the powder substance.