The Synthesis and Analysis of Aspirin Salicylic Acid Standard Stock Solution Ini

Question

The Synthesis and Analysis of Aspirin Salicylic Acid Standard Stock Solution Initial mass of salicylic acid (g) Moles of salicylic acid (mol) Initial molarity of salicylic acid (M) 6.203 6.064641 ynols t Ill Beer's Law Data for Salicylic Acid Standard Solutions Trial Absorbance 0.1a0 0.34 Concentration (M) b 06088763 6.600245 0.08o 146 41 297 6 149 4 2.S 100 Best-fit line equation for the salicylic acid standards | TI 80 4-ner est of the Purity of the Synthesized Aspirin Initial mass of aspirin sample (g) Absorbance of aspirin sample Moles of salicylic acid in aspirin sample (mol) Mass of salicylic acid in aspirin sample (g) Mass of aspirin in sample (g) Percent aspirin in sample (%) o. 3 3

Explanation / Answer

Ans. The trendline equation (standard curve equation) is in form of y = mx + c.

In the graph, Y-axis indicates absorbance and X-axis depicts concentration. That is, according to the trendline (linear regression or standard curve equation) equation y = y = 1190.4x - 0.0629 obtained from the graph, 1 absorbance unit (1 Y = Y) is equal to 1190.4 units on X-axis (concentration) minus 0.0629.

#1. Moles of salicylic acid in aspirin sample:

Given, absorbance of 100-mL aspirin aliquot = 0.338

Putting y = 0.338 in trendline equation-

            0.338 = 1190.4x – 0.0629

            Or, x = (0.338 + 0.0629) / 1190.4

            Hence, x = 3.376 x 10-4

Note that, the X-axis in graph represents CONCENTRATION of salicylic acid in terms of molarity.

Therefore, [Salicylic acid] in aspirin aliquot = 3.376 x 10-4 M

# We have, the final volume of aliquot = 100.0 mL = 0.100 L

Now,

Moles of salicylic acid in aspirin aliquot = Molarity x Vol. of aliquot in liters

                                                            = 3.376 x 10-4 M x 0.100 L

                                                            = 3.376 x 10-3 mol             

#2. Mass of salicylic acid in aspirin sample:

Mass of salicylic acid in aspirin sample = Moles of salicylic acid x Molar mass

                                                = 3.376 x 10-3 mol x (138.121 g/ mol)

                                                = 0.466 g

#3. Stoichiometry: 1 mol salicylic acid forms 1 mol aspirin (acetylsalicylic acid). So, moles of aspirin in sample must be equal to the moles of salicylic acid in it.

So,

            Moles of aspirin (acetylsalicylic acid) = 3.376 x 10-3 mol

            Mass of aspirin = 3.376 x 10-3 mol x (180.16 g/ mol) = 0.61 g

#4. % aspirin = (Experimental mass of aspirin / Mass of sample taken) x 100

                        = (0.61 g / 0.49 g) x 100

                        = 124.5 %

# Note: A % purity value greater than 100% indicates experimental errors. Please review the experiment.

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