Determination alkalinity

Alkalinity. The alkalinity of a water sample is its acid-neutrali2ing capacity. Bicarbonate and carbonate ions are the predominant contributors to alkalinity in most waters, and their chemical equiUbria generally maintain the pH of 5—9. The presence of enough hydroxide ion to affect the alkalinity determination in natural waters is rare. SiUca, borate, or phosphate do contribute to the overall alkalinity if present in large enough quantities. 

The maintenance of lime-treated muds consists of monitoring the calcium content, i.e., the proper lime solubility. Since the lime solubility is controlled by the amount of caustic soda present in the mud, the proper alkalinity determination is of great importance. The recommended value of is 5 to 8, and it is maintained with caustic soda the recommended value of P is 25 to 40, and it is maintained with excess lime. The amount of excess lime should be from 5 to 8 Ib/bbl. 

Among the possible analytical methods for alkalinity determination, Gran-type potentiometric titration [2] combined with a curve-fitting algorithm is considered a suitable method in seawaters because it does not require a priori knowledge of thermodynamic parameters such as activity coefficients and dissociation constants, which must be known when other analytical methods for alkalinity determination are applied [3-6],... 

Ben Yaakov and Lorch [8] identified the possible error sources encountered during an alkalinity determination in brines by a Gran-type titration and determined the possible effects of these errors on the accuracy of the measured alkalinity. Special attention was paid to errors due to possible non-ideal behaviour of the glass-reference electrode pair in brine. The conclusions of the theoretical error analysis were then used to develop a titration procedure and an associated algorithm which may simplify alkalinity determination in highly saline solutions by overcoming problems due to non-ideal behaviour and instability of commercial pH electrodes. 

Pore waters were analyzed for pH, alkalinity, salinity, and sulfate concentration following centrifugation. pH was measured with a Ross combination electrode standardized with commercial NIST traceable buffers. Alkalinity determinations were made by a single addition of 0.01 N HCL (5). Salinity was determined with a refractometer, and with an accuracy of +/- 0.5 o/oo. Sulfate was determined turbidimetrically (6). 

Ammonium phosphates usually are manufactured by neutralizing phosphoric acid with ammonia in which control of the pH (acidity/alkalinity) determines which of the ammonium phosphates will be produced. 

Bound H20 and OH". Spectral data (2 11-13. 18, 21) thermodynamic data (e.g. 86, 87), alkalinity determinations (16), DTA (23). NMR (21), and X-ray diffraction data (21, 23) have all indicated the presence of bound H20 and OH in many carbonate skeletons, particularly high I g calcites. Lowenstam (88)) has reported monohydrocalcite and amorphous hydrated CaCO in some mollusk and arthropod samples. 

When the data for both photometric and titrimetric results are fitted, the corresponding values by alkaline determinations range from 50 to 80% of the neutral reagent result. 

These simple equations and ideas provide the basis for describing the carbonate system in terms of the/coj, DIG, pH, and alkalinity of seawater. We will build up a plot similar to that in Fig. 4.1 for the important acids and bases in seawater. These are listed along with their concentrations and apparent equihbrium constants in Table 4.1. It will then be demonstrated how the constraint of charge balance (called alkalinity) determines the pH of seawater. 

It means the sum of organic acids in wine determined by HPLC have to be lower than the sum total acidity and wine ashes alkalinity determined by titration. 

Dissolved organic carbon (determined by combustion at 680 °C on a Shi-rnadzu TOC-500 instrument) was about 3.5 mg/L and varied little in samples from different depths and times. Alkalinity (determined by Gran plot titrations) was 3-4 mmol/L, and pH varied with depth and time in the range 7.5-8.5 (21). Dissolved phosphate and silicate were measured in filtered samples by standard automated (Auto-Analyzer) methods (25). 

The protonation of organic acid anions during alkalinity titration can cause serious errors in alkalinity determination and the use of the data for carbonate speciation and equilibrium chemical modeling. Errors in alkalinity depend on the same factors as for anion-cation balance and may vary from negligible values to as much as 1270% error as documented by Beck et (1974). Accurate values for alkalinity and carbonate speciation can be determined by direct measurement of CO2 evolved from acidified water samples. 

This is probably the simplest method of testing for carboxyl groups which, since they are a product of alkaline oxidation, will be present as —COONa. A sample is steeped in n/10 sulphuric acid for 1 hour, and next washed twelve times with distilled water. The material is then steeped in fresh distilled water for 3 hours, rinsed and dried. In this way all the alkaline ash-forming constituents, other than the —COONa groups, are removed. After this treatment the sample is weighed and then ignited in a silica crucible and heated until all the carbon has gone. The residue is dissolved in water and the alkalinity determined by titration with N/10 sulphuric acid. 

Gieskes, J. M., and Rogers, W. C. (1973). Alkalinity determination in interstitial waters of marine sediments. J. Sediment. Petrol. 43, 272-277. 

The technical description of this method for alkalinity determination is shown in reference (Radojevic Bashkin, 1999, 180-189). 

The three principal contributors to alkalinity are hydroxide (OH ), carbonate (C03 ) and bicarbonate (HC03 ) ions. It is possible to calculate the contribution of each of these to the alkalinity on the basis of the alkalinity determination, if it is assumed that other species do not contribute to the alkalinity and if is assumed that OH and HCO3 cannot coexist. The following alkalinity conditions are then possible in the sample (a) hydroxide alone, (b) hydroxide and carbonate, (c) carbonate alone,... 

Lenz, A.T. (1944). Estimation of stream-flow from alkalinity determinations. Trans. AGU 25(6) 1005-1011. 

Generally, in freshwaters total alkalinity determinations are carried out using additions of strong acids (either H2SO4 or HCl in the concentration ranges 0.02-0.1 mol 1 ) to an end point pH of 4.2-5.1, using an appropriate indicator or potentiometer. For accurate analysis determination a two-point or multi-point Gran plot method may be employed. 

About 7-8 grammes of the sample are dissolved in water, and made up to 100 c.c., and the total alkalinity determined by titrating 20 c.c. with N/1 acid, using methyl orange as indicator. To another 20 c.c. is added barium chloride solution (10 per cent.) until it ceases to give a precipitate, the precipitate allowed to settle, and the clear supernatant liquid decanted off, the precipitate transferred to a filter paper and well washed, and the filtrate titrated with N/1 acid, using phenol-phthalein as indicator. The second titration gives the amount of caustic alkali present, and the difference between the two the proportion of carbonate. 

The acidity (or alkalinity, as the case may be) of water is very important because H (aq) and OH (aq) ions play crucial roles in many reactions in aqueous solutions. For example, the acidity (or alkalinity) determines the ability of water to sustain fish and plant life it also determines the solubility of many materials in water. 

Barbiturates in micro amounts determined by shift in spectrum going from pH 10.5 to strongly alkaline determined in extracts from blood at 260 m in 1 AT NaOH before and after addition of ethylenediamine dihydrochloride Chloral hydrate in admixture with trichloroacetic acid and trichloroethanol used reaction with pyridine Strychnine (252 m/i) mixed with brucine (262 m ) [ ]. Theobromine and caffeine in cocoa powders (after separa-tion)[ ]. 

By convention, acidity is defined as milligrams KOH required to bring 1 g of sample to the pH of the phenolphthalein end point. Alkalinity is equivalent milligrams KOH neutralized by addition of acid to reach the end point. This gives a value which can be used directly to correct the hydroxyl number determination (section B.l). This measurement is easily performed and gives an indication of consistency and impurity level for quality control purposes. The pitfalls of acidity and alkalinity determination are discussed in Chapter 1 with the analysis of anionic surfactants. The same procedures are used as for the analysis of anionics. 

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