Qualitative analysis of aspirin and acetaminophen in a sample

 

background [prelab assignment (40 points) due at the begining of lab]

This laboratory activity is based on investigation 9 in your AP chemistry lab manual; thus, it provides some relevant background for the following prelab questions and this laboratory activity. While investigation 9 uses a separatory funnel, you will be using either a large test tube, syringe, or flask in place of the separatory funnel. There are other equipment substitutions due to cost considerations. Nonetheless, this laboratory activity will reinforce the same concepts reflected in the AP chemistry lab manual.

The chemical structure of aspirin (source), acetaminophen (source), and glucose (source) may be used to rationalize the relative solubility of various compounds in nonpolar (i.e. organic) versus polar (e.g. water) solvents.. Over the counter mediations as aspirin and tylenol (i.e. acetaminophen) contain binders, which are polar compounds, while aspirin and acetaminophen are soluble in organic solvents.

The following sequence of questions are designed to guide you in the development of an experimental protocol in your analysis of a sample containing aspirin and / or acetaminophen and / or glucose (to mimic binders). As the experimental protocol will consist of a sequence of steps, which corresponds to the sequence of the below questions, you should answer the below questions in the sequence given below. A flow chart may be used to describe / summarize the experimental protocol.

In regards to the below questions, clearly identify the location of each of the preceding chemicals and the identity of its phase (i.e. gas, liquid, solid, dissolved in water, or dissolved in an organic solvent). [answer]

1. msds of ethyl acetate & HCl. view the video on the effect of acid on protein, e.g. your eyes

2. step 1: goal is to separate polar and nonpolar solutes using ethyl acetate, a nonpolar solvent, and subsequent filtration. identify the type of solutes (i.e. polar versus nonpolar) in the filtrate versus on the filter paper. justify / rationalize your response.

3. describe the use of a separatory funnel and its basis of separating chemicals ? describe a method to differenitate between the organic versus aqueous solvent in the separatory funnel.

4. step 2: aspirin is a carboxylic acid (i.e. a weak acid, HA), which would react with NaHCO3

HA (dissolved in ethyl acetate) + NaHCO3 (aq) → H2O(l) + CO2 (g) + NaA(aq)

on the other hand, acetaminophen will not react with sodium bicarbonate. based on this information and your response to # 3, design the next step in the experimental protocol and state the location of each potential chemical with basis / rationale.

repeat treatment of the ethyl acetate solution with the NaHCO3 solution to ensure separation of chemicals between these two immiscible solvents.

5. step 3a: the preceding salt, NaA, would react with an acid, HCl

NaA(aq) + HCl(aq) → HA + NaCl(aq)

based on this information, design the next step in the experimental protocol and state the location of each potential chemical with basis / rationale.

6. step 3b: what is the use / purpose of a "drying agent" ? add MgSO4, a drying agent, to the organic fraction, then filter.

7. step 4: what is the value / use of a rotatory evaporator in the context of this lab ? based on this information, design the next step in the experimental protocol.

8. to modify step 4 to conserve money, you could use a hot water bath or a hot plate to replace a rotatory evaporator. what is the rationale of using either a hot plate or hot water bath rather than a Bunsen burner as a source of heat in this lab ?

 

purpose

identify the chemical(s) in a sample:

materials

~1 - 3 g sample containing: aspirin and / or acetaminophen and / or glucose

syringe = separatory funnel surrogate

ethyl acetate (~ 50 mL / group)

NaHCO3 (8.4 g / dL; 100 mL / group)

6 M HCl (~ 30 mL / group; add slowly to minimize excessive bubbling)

MgSO4 (~ 1 grams / group)

filter paper, glass funnel, 2, 125 mL flasks; 250 mL beaker, 50 mL gradulated cylinder

methods / data analysis

student design; carefully record your observations and experimental protocol; otherwise, you won't be able to prepare your lab report.

remarks

to ensure that any potential aspirin dissolves, stir / mix mixture for at least 2 mintues in the organic solvent, since it might take aspirin awhile to dissolve

to minimize organic layer contamination of aqueous solution, wait at least 2 minutes after shaking immiscible solvents in the separatory funnel prior to separating these two layers

wait at least 10 minutes after HCl treatment to provide sufficient time for the reaction to occur

dispose of any aspirin via filtration

content of lab report [30 points]

develop a flowchart that describes the experimental protocol and shows the location of each chemical in the mixture at each step; include a basis / rationale for the location of the chemical at each step in the protocol. [20 points]

your experimental observations [5 points]

identify chemicals in your mixture [5 points]

briefly, describe your experimental protocol to separate aspirin, acetaminophen, and glucose in a mixture and the basis of each step in the separation / extraction protocol. also, clearly identify the location of aspirin, acetaminophen, and glucose, i.e. in organic solvent ? in aqueous solvent ? on filter paper ? at each step in the experimental protocol.

experimental results / observations

data analysis: refer to the purpose of this lab activity and justify / rationalize your conclusions. that is, it's an interpreation of your observations.