Equivalent solutions

It has been shown that for most acid-base titrations the inflection point, which corresponds to the greatest slope in the titration curve, very nearly coincides with the equivalence point. The inflection point actually precedes the equivalence point, with the error approaching 0.1% for weak acids or weak bases with dissociation constants smaller than 10 , or for very dilute solutions. Equivalence points determined in this fashion are indicated on the titration curves in figure 9.8. 

Calculate the volume of standard EDTA solution equivalent to the magnesium by subtracting the total volume required for the calcium from the volume required for the total calcium and magnesium for equal amounts of the test sample. 

Discussion. Potassium may be precipitated with excess of sodium tetraphenyl-borate solution as potassium tetraphenylborate. The excess of reagent is determined by titration with mercury(II) nitrate solution. The indicator consists of a mixture of iron(III) nitrate and dilute sodium thiocyanate solution. The end-point is revealed by the decolorisation of the iron(III)-thiocyanate complex due to the formation of the colourless mercury(II) thiocyanate. The reaction between mercury( II) nitrate and sodium tetraphenylborate under the experimental conditions used is not quite stoichiometric hence it is necessary to determine the volume in mL of Hg(N03)2 solution equivalent to 1 mL of a NaB(C6H5)4 solution. Halides must be absent. 

Standardisation. Pipette 10.0 mL of the sodium tetraphenylborate solution into a 250 mL beaker and add 90 mL water, 2.5 mL 0.1 M nitric acid, 1.0 mL iron(III) nitrate solution, and 10.0 mL sodium thiocyanate solution. Without delay stir the solution mechanically, then slowly add from a burette 10 drops of mercury(II) nitrate solution. Continue the titration by adding the mercury(II) nitrate solution at a rate of 1-2 drops per second until the colour of the indicator is temporarily discharged. Continue the titration more slowly, but maintain the rapid state of stirring. The end point is arbitrarily defined as the point when the indicator colour is discharged and fails to reappear for 1 minute. Perform at least three titrations, and calculate the mean volume of mercury(II) nitrate solution equivalent to 10.0 mL of the sodium tetraphenylborate solution. 

Grams of Unknown Solution Equivalent Presumed Formula to 1 Gram of Standard Solution... 

Quantitation is performed by the calibration technique. Prepare a calibration curve by injecting pyrithiobac-methyl standard solutions, equivalent to 0.2,0.5,1.0,2.0,3.0 and 4.0 ng, into the gas chromatograph. Measure the heights of the peaks obtained. Plot the peak heights in millimeters against the injected amounts of pyrithiobac-methyl in nanograms. 

Quantitation is performed by the calibration technique. Construct fresh calibration curves with imibenconazole and imibenconazole-debenzyl standard solutions for each set of analyses. Inject 2 qL of each standard solution (equivalent to 0.04-2 ng of imibenconazole and imibenconazole-debenzyl) into the gas chromatograph. Plot the peak areas obtained versus amount of imibenconazole and imibenconazole-debenzyl injected. 

Assay preparation. Transfer not less than 20 Capsules to a blender jar or other container, and add about 150 mL of methylene chloride, and cool in a solid carbon dioxide acetone mixture until the contents have solidified. If necessary, transfer the mixture of capsules and methylene chloride to a blender jar, and blend with high-speed blender until all the solids are reduced to fine particles. Transfer the mixture to a 500-mL volumetric flask, add n-heptane to volume, mix, and allow solids to settle. Transfer an accurately measured volume of this solution, equivalent to 250 mg of valproic acid, to a 100 mL volumetric flask, dilute with w-heptane to volume, and mix. Transfer 5.0 mL to a container equipped with a closure. Add 2.0 mL of the internal standard solution, close the container, and mix. 

Procedure Dissolve 0.0079 g of pure lead nitrate in 1 litre of DW in a volumetric flask. To 10 ml of this solution (equivalent to about 50 meg of Pb) contained in a 250-ml separatory funnel, add 775 ml of ammonia-cyanide-mixture, and adjust the pH of the resulting solution to pH 9.5 by the careful addition of HC1. Now, add 7.5 ml of dithizone solution and 17.5 ml of chloroform rapidly. Shake the contents of the separatory funnel thoroughly for 1 minute, and allow the phases to separate. Determine the absorbance at 510 nm vis-a-vis a blank solution in a 1.0 cm absorption cell. However, a further extraction of the same solution yields zero absorption thereby indicating that complete extraction of lead has taken place. 

Our "solution value is closer to the 60° mininimum from the statics study. Forcefields such as used by Mardsen et al. are solution equivalent (i.e. contain information on the interactions in aqueous solution). Therefore, their results are not for a truly isolated molecule, but might be expected to be equivalent to our solution model. To allow determinations of conformation in vacuum and other solvents, water information should not appear in the basic potentials. The presence of water information in force fields is a common problem. 

After alkaline saponification, each reaction mixture was divided into three portions %bich were treated as follows 1) Absorbent polymer was methanol-precipitated as is with no adumiium chloride treatment. These products served as controls and provided absorbency vadues that could be conpared with absorbencies presented in earlier tables. 2) Absorbent polymer was methanol-precipitated aifter addition of either 15, 12.5, or 10 g of AlCls 6H20 to the saponiflcate. 3) Polymer was methanol precipitated after adding aduminum chloride followed by an amount of s um hydroxide solution equivalent to that needed to convert alumirum chloride to aduminum hydroxide. Wicking as well as absorbency was then determined both as is and aifter treatment with HCl in methanol to neutralize excess alkali. 

Why is this criterion for the existence of a non-trivial solution equivalent to the one in Problem 7-5 ... 

In order to carry out a ligand screen, the resin bearing the target and reference proteins, which have been immobilized at a solution equivalent of about 100 pM, must be packed into the dual-cell sample holder. A home-made packing reservoir has been built to fit on top of the dual-cell sample holder and double the volume of each cell. The resin (as a 50 %... 

Figure 6.5 Requirement for the presence of detergent while screening micelle-solubilized membrane proteins. In this series of experiments both the target (KcsA) and the reference (OmpA) were immobilized at a solution equivalent of 150pM. The histogram represents the fractional difference in peak amplitude of a known ligand of KcsA in the presence of KcsA and OmpA. The bar labeled control represents the first application of the ligand. Subsequently three injections of the ligand were performed using buffers that contained no detergent. A further three injections were performed where the buffer used to wash the immobilized samples contained deuterated DPC.

The time constant ti,vdv may be estimated with the "solution-equivalent" of Eq. (15.94) ... 

Assay Transfer an accurately weighed amount of Sample Solution, equivalent to about 1 g of CaCl2, into a 250-mL... 

---