Tartaric acid is a diprotic acid (H2T) present in many fruits and is
used in cosmetics due to its powerful depigmenting effect. Therefore, it is
present in multiple facial creams whose pH is 5.2. Calculate the amount of H2T that is
you must add to prepare 125 mL of a necessary tartaric acid solution in the
manufacture of such creams. Data: Ka1 = 9.2 x 10-4; Ka2 = 4.31 x10-5. PM H2T = 150.1g / mol

The enzyme is studied in the presence of a different inhibitor (inhibitor B). In this case, two different concentrations of inhibitor are used. Data are as follows:

a) Determine the apparent Vmax at each inhibitor concentration.

b) Determine the apparent KM at each inhibitor concentration.

c) Estimate KI from these data. [Hint: Calculate the K_I at 3 mM and at 5 mM; and then take the average of the two K_{I }values.]

Sodium sorbate (HS) and sodium benzoate (HBz) are additives used together
in many foods to inhibit the growth of microorganisms. In particular, it
they are present in jams in the following amounts, sodium sorbate
(150.22 g / mol) 44 mg / kg and sodium benzoate (144.11 g / mol) 26 mg / kg. 10 g of
jam and dissolve in H2O until a total volume of 70 mL is obtained. Determines
the pH of the resulting solution assuming they are the only acid / basic species
existing in the mix. Ka sorbic acid (HS) = 1.74 x 10-5, Ka benzoic acid (HBz) =6.28 x 10-5.

You need to prepare an acetate buffer of pH 5.31 from a 0.809 M acetic acid solution and a 2.81 M KOH solution. If you have 880 mL of the acetic acid solution, how many milliliters of the KOH solution do you need to add to make a buffer of pH 5.31 ? The p K a of acetic acid is 4.76.

For the reaction A+B+C→D+EA+B+C→D+E, the initial reaction rate was measured for various initial concentrations of reactants. The following data were collected:

Rate law equation

The rate of a chemical reaction depends on the concentrations of the reactants. For the general reaction between AA and BB,

aA+bB⇌cC+dDaA+bB⇌cC+dD

The dependence of the reaction rate on the concentration of each reactant is given by the equation called the rate law:

rate=k[A]m[B]nrate=k[A]m[B]n

where kkk  is a proportionality constant called the rate constant. The exponent mmm  determines the reaction order with respect to AA, and nnn determines the reaction order with respect to BB. The overall reaction order equals the sum of the exponents (m+nm+n).

Part A: What is the reaction order with respect to A? **Express your answer as an integer.

Part B: What is the reaction order with respect to B? **Express your answer as an integer.

Part C: What is the reaction order with respect to C? **Express your answer as an integer.

Calculate the percent ionization of hypobromous acid (HBrO) in solutions of each of the following concentrations (Ka = 2.5e-09.)

(a) 0.142 M

= %

(b) 0.448 M

= %

(c) 0.625 M

= %

1.            Consider the following redox reaction to produce methanol:

                                    2CH₄(g) + O₂(g) --> 2CH₃OH(g).

a. Calculate the change in enthalpy for the reaction at standard conditions using bond dissociation energies. See the b. appendix for the table of bond energies.

b. Name two things that you could do to favor the formation of methanol by this reaction.

c. Using the value of ∆H calculated in 1a, is this an exothermic or endothermic reaction? Explain your answer.

d. Methane gas is a byproduct of oil extraction and of oil refining. Release of the methane gas into the atmosphere, which contains 20% oxygen, does not result in the formation of methanol. That’s a surprising observation: Despite the fact that the reaction of methane and oxygen to produce methanol is product-favored at normal temperatures, methanol is not formed spontaneously when methane is released to the atmosphere. Suggest why no methanol is formed.

Differentiate between total ion chromatogram (TIC) and extracted ion chromatogram (EIC). Why quantification of analytes is carried out through integration of EIC?

Selected ion monitoring (SIM) is often used in determination of analytes at trace levels, (very low concentrations) provide a brief explanation why one obtains lower detection lim-its with SIM than SCAN.

Discuss the need for rapid scan or MIM data acquisition with mass spectrometers when interfaced with chromatography techniques.

In a titration of 47.63 mL of 0.3786 M nitrous acid with 0.3786 M aqueous sodium hydroxide, what is the pH of the solution when 47.63 mL of the base have been added?

Describe the physical effects and interferences that the method of standard additions would correct or compensate for in AAS.

this question came straight from the textbook... no other explanation was given

THIN LAYER CHROMATOGRAPHY OF ANALGESICS

Introduction:

Analgesics are compounds that relieve pain. They range from over the counter drugs such as aspirin, which is consumed at a rate of 40 million pounds per year, to prescription drugs like morphine and other related narcotics. In addition to aspirin, several other chemically similar compounds are widely used in nonprescription analgesic tablets. The most common non-aspirin pain relievers are acetaminophen and ibuprofen. Caffeine, a stimulant, is sometimes added to analgesic formulation to overcome drowsiness. In addition to the active ingredients, the tablets of these drugs also contain starch, lactose, and other substances that act as binders and permit rapid solution.

Over-the-counter analgesics typically contain one or more of the following active ingredients: acetaminophen, aspirin, caffeine, ibuprofen or naproxen. Thin layer chromatography (TLC) offers a simple method of analysis for these products.

Chromatography is a term that is widely used to describe a family of closely related separation methods. There are many separation methods, but the feature that distinguishes chromatography from other physical and chemical methods of separation is both a stationary and mobile phase; the sample to be separated interacts numerous times with these phases. The sample is carried through the system via the mobile phase, and the interactions that occur are due to the differences in the physical and chemical properties. These differing affinities govern the rate at which the individual components of the sample pass over the stationary phase under the influence of the mobile phase.

Thin layer chromatography (TLC) is one type of chromatography where the stationary phase is a thin layer of adsorbent particles attached to the solid plate. A small amount of sample is applied (spotted) near the bottom of the plate, and the plate is placed in the mobile phase. This solvent is drawn up by capillary action to a predetermined height. Each component, being different in chemical and physical composition and polarity, will interact with the stationary phase at a different time (retention time), thereby creating the individual bands on the plate. The retention time or retention factor (Rf) is used to characterize and compare components of various samples.

Rf = distance from origin to center of spot distance from origin to solvent front

Analysis of an analgesic by TLC.

You will perform TLC experiments using commercial TLC plates prepared by depositing a thin layer of silica gel onto a plastic sheet just like to ones you used last week. These are convenient for the student lab, but are less efficient than the glass-backed plates normally used in research laboratories. Great care should be taken to label the origin and the solvent front, as well as the source of each of the spots for future reference. Mark very lightly with a pencil on the coated side of the plates, being careful not to flake off the silica gel. Do not touch the plates on the active surface and make sure that the solvent front travels evenly up the plate, so as to result in a straight vertical elution of the samples. The application of very small amounts of the sample as distinct, tight spots on a horizontal origin line will provide the best separation and comparison data. Be especially careful not to contaminate your samples, since the detection method to be used can be very sensitive. Use forceps to carefully insert the plate into the developing jar without splashing solvent and to remove it after development. The plate should be squarely vertical during development to promote an even flow of the solvent up the plate. Note the appearance and position of the spots after developmentof the plate. During visualization under UV light, the spots should be lightly outlined with a pencil on the

C343 Spring 2020: TLC plate of analgesics

plate for later reference. Determine the Rf values of the compounds and record these in your lab notebook. Your AI will demonstrate these TLC techniques.

Prepare a table similar to the solvents table, but with the active ingredients of the following analgesics: Advil, Aleve, Anacin, Aspirin, Excedrin, Tylenol. Reference compounds: Naproxen, Ibuprofen, Acetaminophen, Acetylsalicylic acid, caffeine.

Table1. Commercial over-the-counter remedies and their ingredients

You will be given a sample of a commercial headache remedy (half a tablet of an unkown); your task is to identify the active components of this product. Among the common ingredients in over-the-counter preparations are aspirin, acetaminophen, and caffeine. Note which sample you are assigned in your notebook. Prepare a methylene chloride: ethanol (1:1) solution of the soluble components of your sample. The commercial samples contain various binders and other inert materials useful in the formulation of capsules or tablets. These are mostly insoluble in methylene chloride and can be allowed to settle to the bottom of the methylene chloride extract or, if necessary, they can be filtered from the extract.

Use pure known samples provided in the laboratory, as well as the caffeine sample you extracted from tea/coffee (if still around) as authentic TLC references. Examine the methylene chloride extract of the commercial product by TLC to determine which of these ingredients are clearly present in this sample, and which are not present. The use of a solvent mixture of 19:1 ethyl acetate/acetic acid is recommended as an eluting solvent for this TLC determination, 4:1 Ethyl acetate:hexane will also be used for visualizing the less polar compounds. Draw pictures of your TLC plates in your notebook and make TLC plates for your summary using the ChemDraw TLC tool, do not take pictures of your TLC, phones are prohibited in the lab.

In addition to the active ingredients, a number of inert materials are also listed on the label of these products. These might show up as unidentified spots on your TLC plates. Additional spots may also be visible which are derived from decomposition of the active ingredients as they stand in solution.

C343 Spring 2020: TLC plate of analgesics

Procedure:

1. Making your TLC unknown solution. Your AI will assign you an unknown (half a tablet). Make a solution for TLC analysis by taking a small spatula full of your crude mixture in 1:1 ethanol/dichloromethane and shake to help dissolve your components (4-6 mL). Individually create two TLC plates as shown in the picture. You should prepare TLC plates that look like these→

2. Prepping your plate. Draw a pencil line lightly on a
   TLC plate so as not to break through the silica gel
   on the plate. If you scrape the silica gel off the
   plate, it may lead to poor or no elution. Be
   organized and label your spots appropriately. Try
   writing single letter codes under the locations that
   you place your spots and record your labels in your
   notebook so that you do not forget how your results correlate. Remember you will want to write up your observations in the summary. You will analyze the Rfs of the known compounds and then find out what is in your unknown sample.

3. Spotting your plate. When you are ready to spot, it is best for samples to be applied as small (1-2 mm diameter) spots, spot twice waiting for solvent to evaporate between spotting. During development of the plate, spots tend to diffuse (i.e., broaden), so that the final spot is considerably larger than the original spot. The larger the final spot, the more difficult it is to resolveamixtureintocompletelyseparatespots. PlaceonlyasmallamountontheTLCplate, as too much will lead to tailing on the plate and compounds will bleed into each other (i.e., spots will overlap and this is undesirable). If you do have large tailing spots, you can add less to the plate or dilute your initial solution with more solvent. Regardless, calculate an Rf from the middle of the spot. Rinse your spotter between samples!

4. Running the TLC. Once your TLC plates are ready, run The TLC labelled 19:1 in 19:1 ethyl acetate/acetic acid and the 1:2 in Ethyl acetate: Hexanes. Record any observations or problems that arise while performing the experiment.

5. Eluting the plates. Be sure the elution chamber solvent level is below the spot level on the TLC plates. Too high a solvent level will wash the spots off the plate, preventing any meaningful analysis. The plate is placed into the chamber and the solvent is allowed to rise up to within 0.5 cm of the top of the silica gel coating, about 70% the height. Make sure you have a wicking filter paper in the chamber to saturate the atmosphere with solvent during elution.

6. Visualizing your plates. You will visualize your TLC under UV light. Most spots are clear under U.V. TLC plates are commonly stained after visualization under UV light, you will stain one of your TLC plates with PMA TLC stain, DO NOT STAIN YOUR TLC plates until you have visualize

C343 Spring 2020: TLC plate of analgesics

your Rfs.. Use a pencil to indicate the location of spots under UV light, most conjugated compounds appear as violet or purple spots under UV light, if the coating on the plates contains a UV absorber. Refer to the video about PMA staining posted in Canvas. The procedure is not complicated: wet the TLC in the stain, pat it dry moving it to one side, put it upwards on the heating plate until you see the color of the stain.

7. Recording your results. Sketch the TLC plate(s) you have developed in your lab notebook so that you can refer to them again in your summary below. Calculate the Rf values and enter them into your table remaining organized during lab. Do not do this after lab, as you will more likely make mistakes.

Questions:

1a) make a physical properties table (2)

1b ) (1) Explain how and why increasing polarity of the different eluting solvents would affect the

elution of the compounds

1. c) If a less polar TLC development solvent was used, how would that affect the Rf values of

   the reference compounds?

   a. (1)Why was it necessary to run a TLC experiment in a closed container and to have the

   1. interior vapor saturated with the solvent by using a wick?

   2. (2)What will be the result of applying too much compound to a TLC plate? Not enough?

   3. (2)What will be the appearance of a TLC plate if a solvent of too low of a polarity is used

      for its development? Too high of a polarity?

Pentyl Ethanoate, CH3COOC5H11, which smells like bananas, is produced from the esterification reaction:

CH3COOH(aq) +C5H11OH(aq) → CH3COOC5H11(aq) + H2O(l)

A reaction uses 3.58 g of CH3COOH and 4.75 g of C5H11OH and has a yield of 45.00%. Determine the mass of ester that forms.

#6. A 130.0 mL buffer solution is 0.110 molL−1 in NH3 and 0.125 molL−1 in NH4Br.

A) What mass of HCl will this buffer neutralize before the pH falls below 9.00? (Kb(NH3)=1.76×10−5)

B)If the same volume of the buffer were 0.270 molL−1 in NH3 and 0.390 molL−1 in NH4Br, what mass of HCl could be handled before the pH fell below 9.00?

Please answer the following questions regarding hydroxyapatite. Please show all work.

a.)    How many atoms are in the unit cell for Hap?

b.)    What are the unit cell parameters? Please use the attached diagram to determine.

c.)    Calculate the unit cell volume for HAp.

d.)    Calculate the density for HAp.

e.)    Calculate the packing factor for HAp.

f.)     Derive an equation for calculating the specific surface area for hydroxyapatite particles consisting of unit cell dimension particles. Calculate the value for the specific surface area of these particles in meters squared per gram (m^2/g). What is interesting about the magnitude of this number?

g.)    How would you differentiate between a polycrystalline, a single crystalline, and a nanocrystalline sample of HAp?