Examples solutions preparation

A stock solution is prepared by weighing out an appropriate portion of a pure solid or by measuring out an appropriate volume of a pure liquid and diluting to a known volume. Exactly how this is done depends on the required concentration units. For example, to prepare a solution with a desired molarity you would weigh out an appropriate mass of the reagent, dissolve it in a portion of solvent, and bring to the desired volume. To prepare a solution where the solute s concentration is given as a volume percent, you would measure out an appropriate volume of solute and add sufficient solvent to obtain the desired total volume. 

A more challenging problem is to find the pH of a solution prepared from a polyprotic acid or one of its conjugate species. As an example, we will use the amino acid alanine whose structure and acid dissociation constants are shown in Figure 6.11. 

Potassium silicate solutions are equally complex for example, an aqueous solution prepared from KOH and Si02 in which the ratio K Si is 1 1 contains 22 different discrete silicate anions as identified by Si COSY nmr studies. 

Sample preparation for AFM analysis is relatively simple. Generally, a desired amount of sample is absorbed onto a smooth and clean substrate surface, for example, a freshly cleaved mica surface. For example, to prepare a food macromolecule sample for AFM imaging in air, the diluted macromolecule solution is disrupted by vortexing. Then, a small aliquot (tens of microliters) of vortexed solution is deposited onto a surface of freshly cleaved mica sheet by pipette. The mica surface is air dried before the AFM scan. A clean surrounding is required to avoid the interference of dust in the air. Molecular combing or fluid fixation may be applied to manipulate the molecule to get more information. 

Orally administered suspensions containing a wide class of active ingredients (e.g., antibiotics, antacids, radiopaque agents) are of major commercial importance. The solids content of an oral suspension may vary considerably. For example, antibiotic preparations may contain 125-500 mg solid drug per 5 mL or a teaspoonful dose, while a drop concentrate may provide the same amount of drug in only 1-2 mL. Antacid or radiopaque suspensions also contain relatively high amounts of suspended material for oral administration. The suspending vehicle can, for example, be a syrup, sorbitol solution, or gum-thickened water with added... 

EXAMPLE 10.4. What is the molarity of a solution prepared by dissolving 117g NaCI in enough water to make 500 mL of solution ... 

EXAMPLE 10.12. (a) What are the molarities of the ions in a solution prepared by dissolving 3.0 mol of AlCl,... 

EXAMPLE 16.3. Calculate the molality of a solution prepared by adding 0.200 mol of solute to 100g of water. 

Dissolve the molecule to be coupled in the same buffer used in step 1. For small molecules, add them to the reaction in at least a 10-fold molar excess to the amount of protein present. If possible, the molecule may be added directly to the protein solution in the appropriate excess. Alternatively, dissolve the molecule in the buffer at a higher concentration, and then add an aliquot of this stock solution to the protein solution. In the example of preparing a peptide-protein conjugate, dissolve the peptide in 0.1 M MES, pH 4.7, at a concentration of up to 2 mg/500 pi. 

Because of these precursor modification reactions, the process chemistry of chelate processes is as complex, or more so, than that involved in sol-gel processes.78 However, it is typical for chelate processes that some control of process chemistry is sacrificed in return for more expedient solution preparation. For example, the hour-long (or longer) reflux processes that have been historically used in 2-methoxyethanol based sol-gel processing of ferroelectric films are not used. Rather, the entire solution preparation procedure is generally completed within one hour, with only the initial phase of the procedure being carried out under dry box and inert atmosphere conditions. Once the chelation reaction(s) has occurred, the hydrolysis sensitivity of the precursor solution is reduced to the point where the remaining process chemistry may be carried out under ambient conditions.46... 

In synthesis B (essentially based on example 1 of ref. 35), an acidic solution, prepared by mixing A1 sulfate (AI2(804)3. 

C, V, B, and A have the same meanings as they do in Equation (4.2). For solution preparation, VB, the volume of the solution to be diluted (the volume before dilution), is calculated so that the analyst can know how much of this more concentrated solution to measure out in order to prepare the less concentrated solution. Remember that VB and VA can have any volume unit, but the units for both VB and VA must be the same (for example, milliliters). The same is true of the concentration units. 

It should be stressed that the pH value of an actual buffer solution prepared by mixing quantities of the weak acid or base and its conjugate base or acid based on the calculated ratio will likely be different from what was calculated. The reason for this is the use of approximations in the calculations. For example, the molar concentration expressions found in Equations (5.23) to (5.30), e.g., [H+], are approximations. To be thermodynamically correct, the activity of the chemical should be used rather than the concentration. Activity is directly proportional to concentration, the activity coefficient being the proportionality constant ... 

For example, to prepare a pH = 9 buffer solution, one would prepare a solution of ammonium chloride (refer to Table 5.1), and then add a solution of sodium hydroxide while stirring and monitoring the pH with a pH meter. The preparation is complete when the pH reaches 9. The required conjugate acid-base pair would be NH3 - NHj. Recipes for standard buffer solutions can be useful. Table 5.2 gives specific directions for preparing some popular buffer solutions. 

Another example of the preparation of parts per million solutions is by dilution. It is a very common practice to purchase solutions of metals that are fairly concentrated (1000 ppm) and then dilute them to obtain the desired concentration. This is done to save solution preparation time in the laboratory. As per the discussion in Chapter 4, (see Equation (4.14) and the accompanying discussion), the concentration is multiplied by the volume both before and after dilution. Using the parts per million unit, we have... 

Suppose you followed the procedure in Example 5.12, but did not weigh exactly 1.861 g, but came close with 1.9202 g. What is the molarity of the EDTA solution prepared with this weight of solute ... 

The activities carried out in a wet lab would probably include sample preparation and wet chemical analysis procedures (for example, extractions, solution preparations, and titrations)—activities that do not utilize sophisticated electronic instrumentation. 

For example, determine the volume percentage of carbon tetrachloride in a solution prepared by dissolving 100.0 mL of carbon tetrachloride and 100.0 mL of methylene chloride in 750.0 mL of chloroform. Assume the volumes are additive. 

For example, ethylene glycol (C2H602) is used in antifreeze. Determine the molality of ethylene glycol in a solution prepared by adding 62.1 g of ethylene glycol to 100.0 g of water. 

For example, a solution prepared by dissolving 8.95 mg of a gene fragment in 35 0 mL of water has an osmotic pressure of 0.335 torr at 25-0°C. Assuming the fragment is a nonelectrolyte, determine the molar mass of the gene fragment. 

Dibenzoylmethane (8b) has been the subject of much interest as regards the possibility that its polymorphism is associated with keto-enol tautomerism. Chemical and spectroscopic studies showed that this is not so (33a). This compound had previously been reported to be trimorphic (33b), but one form appears, in fact, to be a eutectic mixture of the other two. The molecules in these two polymorphs are both in the same state of tautomerism they differ in the torsional angle about the (CH)-(CO) bond and in the type of hydrogen bonding in which they participate. It is noteworthy that solutions prepared from these forms at low temperature have differences in chemical and spectroscopic properties that are maintained for some time. For example, such solutions prepared and held at —35° react at different rates with FeCl3. 

O Sodium phosphate, Na3P04, is sold at hardware stores as TSP (trisodium phosphate). Crystals of Na3P04 are dissolved in water to make an effective cleaning solution. TSP can be used, for example, to prepare a surface before painting. 

The recovery of the main compound (100%) and all relevant impurities spiked with, for example, 0.5% wt/wt of a recent and worst-case sample batch, is calculated against a reference solution prepared according to the conditions as described per experimental run of the design. This is done to demonstrate effects of the studied parameters on the extraction of the main compound and the relevant impurities. 

A100 ml flask is fitted with an adapter (see Sect. 2.2.5.3), flamed under vacuum using an oil pump, and filled with nitrogen. 5 ml of the prepared monomer mixture (see above) are pipetted in, followed by 40 ml of an initiator solution prepared from 50 ml of pure dry nitrobenzene (see Example 3-40) and 300 mg (2.25 mmol) of anhydrous aluminum trichloride.The flask is now removed from the adapter under a slight positive pressure of nitrogen and immediately closed with a ground glass stopper.The flask is briefly shaken and allowed to stand at room temperature for 1 h.The solution is then dropped into methanoi and the copolymer worked up as described above. Yield 40-50% with respect to the monomer mixture. 

The epoxidation of heteroarenes such as furans and indoles generates very labile products, such that the reaction needs to be carried out at subambient temperature. For example, even at —20°C, the epoxide of 2,3-drmethylbenzofuran rearranges to the ortho-quinomethide (equation 5) . To characterize this epoxide by H-NMR spectroscopy, the fully deuteriated DMD-dg solution, prepared in acetone-dg, was employed for the oxidation and the epoxide was detected at —78 °C . Alkynes lead on epoxidation to a multitude of oxidation products (equation 6) thus, the reaction is synthetically hardly useful and, therefore, has been little studied . ... 

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