Back titration method

The back titration method can be used to measure total alkalinity with simpler equipment than that required for the potentiometric titrations described above, but at the cost of a poorer precision. The method described is that of Gripenberg (1936) as modified by Koroleff (1972). The sample is acidified with hydrochloric acid to a pH of about 3.5, and the carbon dioxide is driven off by boiling. The solution is then back-titrated to pH 6 with sodium hydroxide solution using bromothymol blue as indicator. The alkalinity is estimated simply as the difference between the amounts of hydrochloric acid and sodium hydroxide added. 

Sodium hydroxide (pro analyst), 0.015 mol/L Dissolve 20g of sodium hydroxide in 20 mL of distilled water, keep in a closed flask several days and then centrifuge transfer 2 mL of the clear supernatant to 2 L of C02-free distilled water. Hie sodium hydroxide solution should be standardized against hydrochloric acid by carrying out the analysis described in Section S.4.3.2 for a distilled water sample. 

Bromothymol blue indicator. Dissolve 100 mg of indicator in 1.6 mL of 0.1 mol/L sodium hydroxide solution and dilute to 100 mL. 

Reference solution for endpoint determination To 120 mL of seawater add 0.4 mL of bromothymol blue solution and adjust the pH (by measurement with a pH meter) to 6.0 (6.6 for Baltic Sea water) with boric acid. 

---

Other detection methods are based on optical transmittance [228-231], Alcohol sulfates have been determined by spectrophotometric titration with barium chloride in aqueous acetone at pH 3 and an indicator [232] or by titration with Septonex (carbethoxypentadecyltrimethylammonium bromide) and neutral red as indicator at pH 8.2-8.4 and 540 nm [233]. In a modified two-phase back-titration method, the anionic surfactant solution is treated with hyamine solution, methylene blue, and chloroform and then titrated with standard sodium dodecyl sulfate. The chloroform passing through a porous PTFE membrane is circulated through a spectrometer and the surfactant is analyzed by determining the absorbance at 655 nm [234]. The use of a stirred titration vessel combined with spectrophotometric measurement has also been suggested [235]. Alternative endpoint detections are based on physical methods, such as stalag-mometry [236] and nonfaradaic potentiometry [237]. 

In this experiment the neutralizing power of various antacids will be determined. Antacids contain basic compounds that will neutralize stomach acid (stomach acid is HC1). The amount of base in the antacid tablets will be determined by an acid-base titration. It is a back titration method. This method is used because most antacids produce carbon dioxide gas, which can interfere with the titration. By initially adding an excess of acid, one can drive off the C02 by boiling the solution before titrating the excess acid. There are many brands of commercial antacids with various ingredients. A few of the common ones are listed below ... 

In this work, halogens were added across the double bonds of unsaturated fatty acids (commercial available sunflower oil) to form addition compounds and the degree of uptake was measured. A measured excess of iodine monobrontide (IBr) was allowed to react with the oil in the dark. At the end of a timed period, an excess of K1 was added to convert the remaining IBr to The 1 formed was then titrated with standard thiosulfate. This was a back-titration method. A back-titration blank was also required, where the sample was omitted. The uptake of iodine was calculated... 

Because the end point (formation of a permanent brownish coloration) is not very sharp, the back titration method (Ref 4) was used successfully by Dr Fedoroff at the Keystone Ordn Works, Meadville, Pa and improved at PicArsn (Ref 9a). More recently, an electrometric method for detection of the end point was proposed (Refs 5, 6, 7, 8 and 11 Refs 6 7 are discussions of instrumental design and not primarily about FeS04 to detn nitrate). 

The method developed at PicArsn for detn of N in NC is described in detail in Ref 18 In the back titration method an excess of FeS04 is added to the soln of the nitrate and back fitrated with K2Cr207 (Ref 4). In addn to the use of K3Cr207, Kolthoff et al... 

The residues of the organic portion of (he molecule remaining could be oxidized by the potassium dichromate used in (he back titration method and so introduce errors. The dead stop method or the colorimetric method (below) might be preferred in such cases... 

If more accurate results are desired, use the "back titration method described under Cellulose Nitrate, Analytical Procedures,... 

In the back-titration method, a measured amount of an excess standard EDTA solution is added to the sample. The analyte ion combines with EDTA. After the reaction is complete, the excess EDTA is back-titrated against a standard solution of magnesium or zinc ion. Eriochrome Black T or Calmagite is commonly used as an indicator. After all the remaining EDTA chelates with Mg2+ or Zn2+, ary extra drop of the titrant solution imparts color to the indicator signifying the end point. The cations that form stable complexes or react slowly with EDTA can also be measured by the back-titration method. 

The TBN values obtained for the fresh, unused, lubricating oil additive package components show results from conductometric and IP 177 (potentiometric) methods being 90% to 98 % and 85% to 90%, respectively, of the corresponding IP 276 (potentiometric) values. The TBN values for some selective products such as zinc dialkyl-dithiophosphate (ZDDP) was observed as an inflection point using the IP 276 (potentiometric) back titration method and also the conductometric method. 

Method C The calorimetric back titration method, the sample of engine oil was dissolved in a mixture of toluene-isopropanol-water (50 49.5 0.5,v/v) and 0.25 M HC104 in isopropanol-toluene (1 1) was used as the titrant the excess acid was titrated by 1 M (CH3)4NOH in isopropanol. Method D The determination of the TAN and AH was performed by direct calorimetric titration. (CH3)4NOH in isopropanol was used as the titrant and a toluene-isopropanol-water (50 49.5 0.5,v/v) was used as the solvent... 

Testing Compounds for Antiviral Activity Using a Back Titration Method... 

The calculation of the content of resorcinol in the solution is identical to the back titration method explained above for lithium carbonate. Consequently, the volume of added bromate is modified by the bromate factor and the thiosulfate titre volume is modified by the thiosulfate factor. A blank titration is not required for this assay since no heating or cooling of the reaction is involved. 

In case of materials showing some degree of solubility the problem how to subtract the blank" is not trivial. Schulthess and Sparks proposed a back titration method to determine the surface charge density of such materials [45]. In this method a series of solutions of different pH is prepared and the solid is added to each solution. After certain time necessary to reach equilibrium a sample of supernatant is taken from each suspension and it is titrated back to the original pH value (before addition of solid). This method was designed to distinguish between surface charging and uptake/release of protons by soluble species. The volume of titrant is then substituted to Eq. (3.1) to obtain (Tq as discussed above for the pH and cip results, and the results obtained by back titration method are listed as pH and cip in Table 3.1. 

In classical potentiometric titration, soluble species produced by dissolution of the solid may contribute to the consumption of an acid or base and induce an error in the calculated Oq. This error is not corrected for in back titrations of an inert electrolyte (Figure 2.6). The back-titration method was designed to avoid the error induced by the dissolution of the solid phase, and it has been used for solids that show appreciable solubility. For solids that are practically insoluble, the... 

The total acidity of the different samples were measured by back titration method [8] and the results are shown in Table-2. 

Ethylenediaminetetraacetic acid can be used as a reagent for the titration of Ti(lV). However, the reaction proceeds slowly, and the Ti(IV) species tend to hydrolyze during the titration, so that a back-titration method is necessary to make the complexometric method work properly [26]. 

Some however prefer to work at low temperature (e.g. 77 K) to ensure that a complete monolayer remains on the metal and that spillover is absent. It is then necessary to estimate the amount of physical adsorption that has to be subtracted from the total, either by measuring the adsorption isotherm for the support alone, or, more reliably the isotherm on the catalyst, following the first adsorption and a short evacuation. This method is referred to as the back titration method (Eigure 3.13), and even at ambient temperature the second isotherm often reveals some weak adsorption , the nature of which may vary from one system to another, and which needs to be taken from the total in order to isolate the amount of the strong form . This often leads to an isotherm that is flatter in the high-pressure... 

Figure 3.13. Measurement of hydrogen chemisorption isotherm by the back-titration method (1) first isotherm, (2) second isotherm measured after short evacuation, (3) the difference.

Back-titration method for the determination of "free, dissolved carbon dioxide"... 

Acid and base concentrations in back titration method, mol/L Carbonate contribution to Ht... 

A potentiometric back-titration method of excess barium ions following precipitation as BaS04 (Mucci, 1991) is outlined in Section 11.2.5.6. 

Magnesium oxide is not very soluble in water, and is difficult to titrate directly. Its purity can be determined by use of a back titration method. 4.08g of impure magnesium oxide was completely dissolved in lOOcm of 2.00 mol dm aqueous hydrochloric acid. The excess acid required 19.7cm of 0.200moldm aqueous sodium hydroxide for neutralization. Work through the following steps to find out what the purity of the impure magnesium oxide is. 

---