Determination calcium hardness

Determining calcium levels normally does not identify hardness breakthrough because the calcium salt simply reacts with phosphate precipitant (or similar treatment) and is lost as a sludge. It does, however, produce an immediate and noticeable reduction in alkalinity. (Calcium bicarbonate breaks down to calcium carbonate and carbonic acid.)... 

EDTA titrations are routinely used to determine water hardness in a laboratory. Raw well water samples can have a significant quantity of dissolved minerals that contribute to a variety of problems associated with the use of such water. These minerals consist chiefly of calcium and magnesium carbonates, sulfates, etc. The problems that arise are mostly a result of heating or boiling the water over a period of time such that the water is evaporated, and the calcium and magnesium salts become concentrated and precipitate in the form of a scale on the walls of the container, hence the term hardness. This kind of problem is evident in boilers, domestic and commercial water heaters, humidifiers, tea kettles, and the like. 

To calculate the soda ash requirement for the calcium noncarbonate hardness by-product, let M gca represent the mass of the magnesium species that precipitates and results in the production of the additional calcium hardness cation, where the Ca, again, is written as a reminder. Refer to Eqs. (10.17), (10.18), and (10.19) to see how the calcium hardness is produced from the precipitation of noncarbonate magnesium. The number of equivalents of the calcium hardness produced is equal to the number of equivalents of the noncarbonate hardness of magnesium precipitated [which is equal to MMgCa/(Mg/2), where Mg/2 is the equivalent mass of Mg as obtained from Eqs. (10.17), (10.18), and (10.19)]. Because this is calcium hardness, we aheady have the method of determining the amount of soda ash needed to remove it as shown in Equation (10.25). Letting this amount be is... 

These complexes are weak enough that, in the complexometric titration determination using EDTA, they break and are included in the total calcium hardness reported. Thus, the total calcium hardness is composed of the legitimate cation, Ca, plus the complex ions as shown in the previous equations. This total calcium hardness must be corrected by the concentrations of the complexes in order to determine the correct activities of the calcium ions. Let the total concentration of the calcium species as determined by the EDTA titration be [Car]. Thus, the concentration of the calcium ion [Ca a )] is... 

Numerous tertiary amines that also contain carboxylic acid groups form remarkably stable chelates with many metal ions. Ethylenediamine tetra-acetic acid (EDTA) can be used for determination of 40 elements by direct titration using metal-ion indicators for endpoint detection. Direct titration procedures are limited to metal ions that react rapidly with EDTA. Back titration procedures are useful for the analysis of cations that form very stable EDTA complexes and for which a satisfactory indicator is not available. EDTA is also used for determining water hardness the total concentration of calcium and magnesium expressed in terms of the calcium carbonate equivalent. 

The determination of hardness is a useful analytical test that provides a measure of the quality of water for household and industrial uses. The test is important to industry because hard water, on being heated, precipitates calcium carbonate, which clogs boilers and pipes. 

The formation constants of the EDTA complexes of calcium and magnesium are too close to differentiate between them in an EDTA titration, even by adjusting pH (see Figure 9.4). So they will titrate together, and the Eriochrome Black T end point can be used as above. This titration is used to determine total hardness of water, (Ca " plus Mg " —see Experiment 9). Eriochrome Black T cannot be... 

This hardness, which can be removed by heating, is called temporary or carbonate hardness. Temporary hardness is derived from contact with carbonate (limestone and dolomite). Hardness which cannot be removed by boiling is called permanent or non-carbonate hardness and it is due to anions, such as chloride, nitrate, sulfate and silicate. This hardness does not contribute to scale formation. Contact with gypsum would result in permanent hardness. Calcium hardness is that due to Ca only, while magnesium hardness is due to Mg only. Magnesium hardness can be calculated from a determination of total and calcium hardness ... 

Alkalinity and calcium hardness of circulating water build up to a level determined by allowable operating concentrations. System pH usually plateaus in the stabilization range of pH8 to 9. So long as the Lange-lier Saturation Index of concentrated cooling water can be kept below +2.0 by bleedoff, supplemental acid feed is not required for scale control. 

The LSI deals with the conditions at which given water is in equilibrium with calcium carbonate and provides a qualitative indication of the tendency of calcium carbonate to deposit or dissolve. The index is determined by subtracting from the actual pH of the water sample (pHA) a computed value (pHS) based on the ppm of calcium hardness as CaCOa, alkalinity hardness as CaCOa, and total solids, as shown in Figure 4.4. If the index is positive, calcium carbonate will tend to deposit. If it is negative, calcium carbonate will tend to dissolve. 

If the calcium complex is dissolved in a less polar medium, such as decanol, then all divalent cations are indicated with virtually no selectivity [127]. This exchange system is used as the active phase in electrodes used to determine water hardness. 

It is thus important to determine the relative amounts of calcium and magnesium, for addition of too much lime means that calcium ions are reintroduced into the water, i.e. it becomes hard again, the hardness being permanent. 

The ash content of furnace blacks is normally a few tenths of a percent but in some products may be as high as one percent. The chief sources of ash are the water used to quench the hot black from the reactors during manufacture and for wet pelletizing the black. The hardness of the water, and the amount used determines the ash content of the products. The ash consists principally of the salts and oxides of calcium, magnesium, and sodium and accounts for the basic pH (8—10) commonly found in furnace blacks. In some products potassium, in small amounts, is present in the ash content. Potassium salts are used in most carbon black manufacture to control stmcture and mbber vulcanizate modulus (22). The basic mineral salts and oxides have a slight accelerating effect on the vulcanization reaction in mbber. 

The most important property of the dissolved solids in fresh waters is whether or not they are such as to lead to the deposition of a protective film on the steel that will impede rusting. This is determined mainly by the amount of carbon dioxide dissolved in the water, so that the equilibrium between calcium carbonate, calcium bicarbonate and carbon dioxide, which has been studied by Tillmans and Heublein and others, is of fundamental significance. Since hard waters are more likely to deposit a protective calcareous scale than soft waters, they tend as a class to be less aggressive than these indeed, soft waters can often be rendered less corrosive by the simple expedient of treating them with lime (Section 2.3). 

The hardness of water is generally due to dissolved calcium and magnesium salts and may be determined by complexometric titration. 

The sum of calcium and magnesium ions in the mud determines the total hardness. These ions are analyzed with complexometric titrations using EDTA (versenate). 

A very important ligand (or chelating agent) for titrimetric analysis is the ethylenediaminetetraacetate (EDTA) ligand. It is especially useful in reacting with calcium and magnesium ions in hard water such that water hardness can be determined. The next section is devoted to this subject. 

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