Standard base solution preparation

A standard method for preparing sodium cyclopentadienide (CjHjNa) is by the reaction of cyclopentadiene with a solution of NaNH2 in liquid ammonia. Write a net ionic equation for this reaction, identify the acid and the base, and use curved arrows to track the flow of electrons. 

Discussion. The hydroxides of sodium, potassium, and barium are generally employed for the preparation of solutions of standard alkalis they are water-soluble strong bases. Solutions made from aqueous ammonia are undesirable, because they tend to lose ammonia, especially if the concentration exceeds 0.5M moreover, it is a weak base, and difficulties arise in titrations with weak acids (compare Section 10.15). Sodium hydroxide is most commonly used because of its cheapness. None of these solid hydroxides can be obtained pure, so that a standard solution cannot be prepared by dissolving a known weight in a definite volume of water. Both sodium hydroxide and potassium hydroxide are extremely hygroscopic a certain amount of alkali carbonate and water are always present. Exact results cannot be obtained in the presence of carbonate with some indicators, and it is therefore necessary to discuss methods for the preparation of carbonate-free alkali solutions. For many purposes sodium hydroxide (which contains 1-2 per cent of sodium carbonate) is sufficiently pure. 

A practical problem in solution preparation usually requires a different strategy than our standard seven-step procedure. The technician must first identify a suitable conjugate acid-base pair and decide what reagents to use. Then the concentrations must be calculated, using pH and total concentration. Finally, the technician must determine the amounts of starting materials. The technician needs a buffer at pH = 9.00. Of the buffer systems listed in Table 18-1. the combination of NH3 and NH4 has the proper pH range for the required buffer solution. 

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. 

Based on their use in industrial and domestic applications and abundance in environmental samples, six surfactants were selected by the participants of interlaboratory study I. Two different standard mixture solutions (standards II and 12) were distributed to all participants for the preparation of the calibration graphs. Standard II contained Arkopal N100 (NPEO), Marlamid DF 1218 (coconut fatty acid diethanolamide, CDEA) and Marlon A 350 (linear alkylbenzene sulfonate, LAS) at 1000 mg L-1 for each compound, while standard 12 contained Rewopol NOS 5 (nonylphenol ethoxylate sulfate, NPEO-SO4),... 

Primer Formulations. Coatings were formulated using standard techniques. Mill bases were prepared by dispersing the oligomer solution with pigments (silica, carbon black, titanium dioxide and barium sulfate in a 1 1 1 10 ratio). The viscosity of the formulation was reduced to spray viscosity by addition of solvent. 

The mode of injection in GC-based methods can affect the recoveries of diazinon. In a study of the determination of organophosphorus pesticides in milk and butterfat, it was found that the recoveries of diazinon from butterfat, calculated relative to organic solutions of standard compounds, were 125% and 84% for splitless and hot on-column injections, respectively (Emey et al. 1993). Recoveries from milk were not dependent on the mode of injection. It was concluded that the sample matrix served to increase diazinon transfer to the GC column by reducing thermal stress imposed on the analytes and by blocking active sites within the injector. Therefore, on-column injection should be used in order to prevent bias when organic solutions of standard compounds are used for quantitation if this is not possible, the matrix must be present at low concentrations or the calibration standards must be prepared in residue-free samples to avoid unknown bias. 

The purity of the reference standard used to prepare spiked samples can affect the study data. For this reason, an analytical reference standard of known identity and purity should be used to prepare solutions of known concentrations. If possible, the reference standard should be identical to the analyte. When this is not possible, an established chemical form (free base or acid, salt, or ester) of known purity can be used. Three types of reference standards are generally used ... 

Determination of protein concentration by measuri ng absorbance at 280 nm (A2g0) is based on the absorbance of UV light by the aromatic amino acids tryptophan and tyrosine, and by cystine, disulfide bonded cysteine residues, in protein solutions. The measured absorbance of a protein sample solution is used to calculate the concentration either from its published absorptivity at 280 nm (a280) or by comparison with a calibration curve prepared from measurements with standard protein solutions. This assay can be used to quantitate solutions with protein concentrations of 20 to 3000 pg/ml. 

Protein concentration can also be determined by measuring the intrinsic fluorescence based on fluorescence emission by the aromatic amino acids tryptophan, tyrosine, and/or phenylalanine. Usually tryptophan fluorescence is measured. The fluorescence intensity of the protein sample solution is measured and the concentration is calculated from a calibration curve based on the fluorescence emission of standard solutions prepared from the purified protein. This assay can be used to quantitate protein solutions with concentrations of 5 to 50 (J-g/ml. 

In the field of environmental analyses, the traceability of results of laboratories is not established on a classic common base where one unique standard pure solution or certified reference material (produced by a NMI for instance) is used by all laboratories as a first basic step for calibration and method validation. Many laboratories ensure the traceability of their results by using commercial solutions or by preparing in-house solutions for the calibration of then instruments. The reliability of these... 

Polystyrene Latex (PSL) Bead Solution Filtration Experiments were conducted to obtain filter retention, flow rate, and Ap data for a DI water based PSL bead mix solution prepared using particles ranging from bead diameters of 0.772 to 20 pm. It is a common practice to use PSL bead challenge solutions (created by mixing different size PSL bead standards in specific volumetric ratio to simulate slurry-like particle size distribution for the bead mix solution) to obtain relative quantitative retention data for various filters. These solutions are expected to retain stable PSD and provide more consistent information compared to real CMP slurries, which may change particle characteristics over time. 

Ashing of samples may be defined as heating a substance to leave an ash that is noncombustible and that is soluble in most dilute acid or base solutions. The resulting solution is analysed for elemental composition against certified standards prepared in the same acid... 

Sodium hydroxide is the most common base for preparing standard solutions, although potassium hydroxide and barium hydroxide are also encountered. Because none of these is obtainable in primary-standard purity, standardization of these solutions is required after preparation. 

Standard acid or base solutions can also be prepared with ion-exchange resins. Here, a solution containing a known mass of a pure compound, such as sodium chloride, is washed through the resin column and diluted to a known volume. The salt liberates an equivalent eunount of acid or base from the resin, permitting calculation of the molarity of the reagent in a straightforward way. 

To calibrate according to the internal standard method, the analyte components must exist as reference compounds in sufficiently high purity. To determine the correction terms, a solution is prepared that contains known amounts of the substances of interest and the internal standard. This solution is chromatographed and the correction terms are calculated based on the peak areas with Eq. (200) ... 

Hydrochloric acid is the usual titrant for the titration of bases. Most chlorides are soluble, and few side reactions are possible with this acid. It is convenient to han- e. It is not a primary standard (although constant-boiling HCl, which is a primary standard, can be prepared), and an approximate concentration is prepared simply by diluting the concentrated acid. For most accurate work, the water used to prepare the solution should be boiled, although use of boiled water is not so critical as with NaOH CO2 will have a low solubility in strongly acidic solutions and will tend to escape during shaking of the solution. 

How to prepare standard acid and base solutions, pp. 43, 44 Common laboratory apparatus for handling and treating samples, p. 44 How to filter and prepare precipitates for gravimetric analysis, p. 48 How to sample solids, hquids, and gases, p. 52 9 How to prepare a solution of the analyte, p. 53... 

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