5.1.6: Solubility of OTC drugs
- Page ID
- 242454
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Lab #6 (follow-up of lab 5, polarity of solvents)
Solubility – a matter of life and death
We will explore the solubility of six different over-the-counter drugs (aspirin, ibuprofen, vitamin C, caffeine, aspartame and acetaminophen). All of these solids are substances that people ingest, either as part of their diet, as stimulants or as drugs. The way these substances distribute in the human body depends on their solubility in water and in non-polar solvents. Very polar or ionic substances will not be able to cross the non-polar lipid bilayer in the cell membranes unless there is a specific transporter present. On the other hand, non-polar substances might not be soluble in the aqueous environment of the digestive tract and the inside of cells. Your group will choose one of the solids to work on. In the experiment today, you will test the solubility of your solute (a) in water and (b) in a solvent of your choice, and use molecular models to relate structure, polarity and solubility. Each group will work with a different solute. The solvent choices are methanol, ethanol, isopropanol, n-butanol, iso-amyl alcohol, acetone, anisole and cyclohexane (cyclohexane is the only solvent we haven’t explored previously – it is non-polar).
Task 1
Look up the structure of your solute, draw it on paper and show any polar bonds and hydrogen bond donors and acceptors. Sketch how your solute would interact with itself in the pure solid. Predict how soluble (very, somewhat, hardly) your solute will be in water. Choose an organic solvent in which you predict different solubility (if you think your substance is soluble in water, choose a solvent you predict low solubility in; conversely, if you think your substance is insoluble in water, choose a solvent you predict high solubility in). Make two drawings, showing solvent-solute interactions in water and in the solvent of your choice. Keep these drawings for the lab report.
Task 2
Come up with an experiment to test your predictions. You will receive two samples of about 2 mg each of your solute in an otherwise empty 1.5 mL tube. The basic experiment is to add a certain volume of solvent, and to see if everything dissolves. If it does not, try vortexing the tube or flicking it with your finger. If necessary, spin down the tube in a centrifuge to collect the liquid at the bottom. Check for solids on the bottom and on the top of the liquid (solids might float). Write down your procedure and show it to your lab instructor before you start the experimental part of the lab.
Task 3
Test the solubility of your solute in water and the solvent of your choice. In the end, you should have data to say the solubility is more than xxx mg/mL but less than yyy mg/mL in water (or organic solvent). This information should be part of your lab report. If you feel that none of the solute dissolved even at high volumes of solvent, place a drop of the liquid on a watch glass next to a drop of the pure solvent, let the solvent evaporate and observe whether you see any residue (the pure solvent is your negative control).
Task 4
Explore how mixing two solvents changes the solubility of solutes. If your solute was already in solution, will it remain in solution if you add a more polar or less polar solvent? If your solute was insoluble, will it go into solution by adding a more polar or less polar solvent? Choose a solvent (different from those you were already working with today) to add to your two mixtures from task 3. Before you do the experiment, predict what will happen, and write your prediction on the board. Then, test your prediction by adding an equal volume of the new solvent of choice to your mixtures.