Reagent volume, calculation

NO + O2 —> 2 NO2 (all gases). A reaction chamber is charged with 5.00 atm each of NO and O2. If the reaction goes to completion without a change in temperature or volume, calculate the final pressures of each reagent. 

Another method of applying Faraday s law to analysis is to generate a titration reagent by means of a suitable electrode reaction. If a current eflSciency of 100% can be maintained, the rate of addition of reagent can be calculated accurately from the current, and extraordinary precision is attainable (Section 5-2). If the current is maintained accurately at a constant value, a titration can be carried out in which time rather than reagent volume is measured. The end point can be determined by either a visual indicator or instrumental methods. 

To understand the theoretical basis of end points and the sources of titration errors, we calculate the data points necessary to construct titration curves for the systems under consideration. Titration curves plot reagent volume on the horizontal axis and some function of the analyte or reagent concentration on the vertical axis. 

For each of the following precipitation titrations, calculate the cation and anion concentrations at equivalence as well as at reagent volumes corresponding to 20.00 mL, 10.00 mL, and 1.00 mL of equivalence. Construct a titration curve from the data, plotting the p-function of the cation versus reagent volume. 

Type I or calculable method Direct through fundamental laws (1) Mass of reagent (volume) towards mass of sample Titrimetry Coulometry Gravimetry Small uncertainty limited to mass determination and purity of reagent and reaction product... 

For routine analyses it may be advantageous to simplify the calculation by combining the predetermined variables for a specific analytical procedure as a constant term, i.e., nominal thiosulphate concentration, oxygen equivalent and bottle and reagent volumes. 

Freshly opened bottles of these reagents are generally of the concentrations indicated in the table. This may not be true of bottles long opened and this is especially true of ammonium hydroxide, which rapidly loses its strength. In preparing volumetric solutions, it is well to be on the safe side and take a little more than the calculated volume of the concentrated reagent, since it is much easier to dilute a concentrated solution than to strengthen one that is too weak. 

Run a blank on the reagents, but use 0.1M acid and alkali solutions for the titrations calculate the blank to 0.5M sodium hydroxide. Subtract the blank (which should not exceed 0.5 mL) from the volume neutralised by the original precipitate. 

Determine the end point from the plot of current against volume of iron reagent. Calculate the weight of nitrate ion equivalent to 1.0 mL of the 0.4 M iron solution. 

B. Duplication method. This is usually applied as the so-called colorimetric titration in which a known volume (x mL) of the test solution is treated in a Nessler cylinder with a measured volume (y mL) of appropriate reagent so that a colour is developed. Distilled water (x mL) is placed in a second Nessler cylinder together with y mL of reagent. A standard solution of the substance under test is now added to the second cylinder from a microburette until the colour developed matches that in the first tube the concentration of the test solution can then be calculated. The standard solution should be of such concentration that it amounts to no more than 2 per cent of the final solution. This method is only approximate but has the merit that only the simplest apparatus is required it will not be discussed further. 

EXAMPLE 4.7 Calculating the mass of reagent needed to react with a specified volume of gas... 

Results of calculations for Sc = 1000 are given in Table 5.4-23. The total stream of B added was divided into 20 portions (N = 20). Each CPU time was less than 5 s at an integration step size of lO ". The formation of the bisazo product is promoted by poor mixing (low values of E, and, consequently, high values of Da) and high volume ratio of reagent solutions Va/Vb-... 

For the preparation of 2 4-dinitrophenylhydrazones, dissolve the carbonyl compound (say, 0-5 g.) in 5 ml. of ethanol and add the calculated volume of the reagent. If a precipitate does not form immediately, dilute with a little water. Collect the derivative and recrystallise it as above. 

At equivalence, the amounts of known and unknown reagents are the same, so Sample) = (unknown)- Knowing the amount of sample and the volume of solution of the unknown, we can calculate the concentration of the unknown. 

Abstract A preconcentration method using Amberlite XAD-16 column for the enrichment of aluminum was proposed. The optimization process was carried out using fractional factorial design. The factors involved were pH, resin amount, reagent/metal mole ratio, elution volume and samphng flow rate. The absorbance was used as analytical response. Using the optimised experimental conditions, the proposed procedure allowed determination of aluminum with a detection limit (3o/s) of 6.1 ig L and a quantification limit (lOa/s) of 20.2 pg L, and a precision which was calculated as relative standard deviation (RSD) of 2.4% for aluminum concentration of 30 pg L . The preconcentration factor of 100 was obtained. These results demonstrated that this procedure could be applied for separation and preconcentration of aluminum in the presence of several matrix. 

Ninhydrin assay. Our method to determine reactivity towards ninhydrin was a modification of a method described previously (Moore and Stein, 1954 Moore, 1968). Briefly, dried samples were dissolved in 0.10 ml 0.1 M acetic acid and mixed with an equal volume of ninhydrin reagent (Sigma). After 15 minutes in a boiling water bath, samples were diluted with 0.80 ml ethanol/water (1 1 by vol.) and measured for absorbance at 550 nm on a flow-through spectrophotometer (Vitatron). Standards containing 0-0.6 mM leucine in 0.1 M HAc were included. Values were therefore calculated as leucine-equivalents. 

When disodium tartrate dihydrate is used, samples ranging from 50 to 120 mg are dissolved in methanol, and the concentration of the KF reagent is determined. Based on volume of titrant used, the weight of the sample and the percent water in the disodium tartrate dihydrate (15.66% w/w), the standardization factor can be calculated. One pitfall with this method is the solubility of the disodium tartrate dihydrate in methanol. It is recommended that the disodium tartrate dihydrate be finely divided and that a suitable extraction time be given for the solids to dissolve. 

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