Magnesium ions in hard water

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. 

Soaps react with the calcium and magnesium ions in hard water to produce soap curd that greatly reduces its effectiveness. The curds are actually insoluble calcium and magnesium salts. Synthetic laundry detergents have replaced soap for cleaning clothes in the last half century. Synthetic detergents are made from petroleum. They work like soap except they do not react with magnesium and calcium ions to form insoluble precipitates and salts. 

Interest in detergent products derived from renewable resources and with better biodegradability has driven evaluation of oxidized sugars and starches as builders or co-builders in detergents.113 Builders and co-builders complex calcium and magnesium ions in hard water to prevent sealing or deposits due to precipitation of insoluble carbonate salts. In current powder detergents, the builders are usually zeolites used in combination with polycarboxylate polymers derived from synthetic acrylic-maleic acid copolymers.114... 

Such a molecule can cause particles of grease or oil to mix somewhat with water and to be washed from a dirty article. Calcium and magnesium ions in hard water react with stearate ions to form a solid, yielding soap scum. To avoid this problem, chemists developed synthetic detergents that do not form insoluble salts with calcium and magnesium ions. Synthetic detergents are similar to soaps in that they have an ionic end and a large hydrocarbon-like end. 

For example, hard water is caused by the presence of calcium and magnesium ions in solution. Sodium aluminosilicate is a water softener which replaces the calcium and magnesium ions in hard water with sodium ions ... 

Permutit A compound that can soften water. It does this by exchanging its sodium ions for the calcium and magnesium ions in hard water. It consists of sodium aluminum silicate. It is a zeolite. The sodium ions do not form insoluble salts with soap and therefore do not prevent the formation of a lather. The Permutit can be returned to its original state by soaking in brine. 

To avoid these undesirable effects, some people install water softeners in their homes. These devices are charged with sodium ions, usually from sodium chloride, that exchange with the calcium and magnesium ions in hard water. Sodium ions do not form scaly deposits as calcium and magnesium do, and they do not react with soap. However, sodium does increase the risk of high blood pressure and must therefore be avoided by those who have high blood pressure or heart problems. 

Certain impurities often found in tap water reduce the effectiveness of soap. Particularly troublesome are the calcium and magnesium ions in hard water. These ions react with soap molecules to form a slimy, gray scum called curd that deposits on skin when bathing or on the sides of the bathtub producing bathtub ring ... 

Water is softened by removing calcium and magnesium ions from hard water in exchange for sodium ions at sites on cation-exchange resin. Water softeners typically use a gel polystyrene sulfonate cation-exchange resin regenerated with a 10% salt brine solution (25). 

Multimedia filters, which consist of a top layer of coarse and low density anthracite, layers of silica, and then dense finest medium vitreous silicate, remove about 98% of particulates >20 tm. These filters are regularly back-washed to avoid buildup of particulates. Finer filters (S-lO tm) are used to remove suspended matter and colloidal materials. To prevent scaling due to water hardness, sodium ions generated from brine are exchanged with calcium and magnesium ions in the water. Activated carbon or metabisulfite is used to remove chlorine. 

A) Titration with calcium chloride. As was indicated above, these phosphates are widely used in laundry operation and in soap powders, to prevent the calcium and magnesium ions of hard water from giving a precipitate with the soap. The value of a particular phosphate for this purpose depends not only on the amount of calcium or magnesium the phosphate can take up to form a complex ion but also on the stability of this complex. In the procedure to be described, the amount of calcium salt needed to destroy a lather of soap and water containing phosphate is measured. This procedure gives an estimate of the calciumbinding power of the phosphate for this particular application. 

Fignre 6 provides another clear example of the interaction between otherwise harmless water qnahty characteristics and toxicant effects. The toxicity of zinc to rainbow front is clearly correlated in a negative way with water hardness. Similar correlations between metal toxicity and water hardness have been noted for a variety of toxic metals. The mechanism responsible for the correlation is not well understood, and considering the wide range of metals for which the effect has been observed, it is unlikely that exactly the same mechanism is operative in all cases. Water hardness, which is a measnre of the concentration of calcium and magnesium ions in the water, tends to be correlated with a number of other water quality characteristics such as pH and alkalinity. Therefore it is possible that at least in some cases the observed negative correlation between metal toxicity and water hardness actually reflects a cause-and-eflfect relationship with one of these other covariates. 

The primary functions of builders in laundry detergent formulations is to remove hardness ions to protect the surfactant. Calcium and magnesium ions in wash water can react with surfactants to form insoluble or nonfunctional complexes. Builders reduce water hardness by three main mechanisms. Sequestration forms a soluble complex between builder and hardness ions. Precipitation forms an insoluble complex with hardness ions. Ion exchange removes calcium and magnesium ions by replacing them with soluble sodium ions. 

Effects of ethoxylation of alkyl ether sulfates on solubility, surface properties, and detergency have been discussed in the literature. Ethoxylation of alkyl surfactants not only increases solubility, but also helps reduce the tendency for precipitation and decrease in foam volume in the presence of calcium and magnesium ions from hard water. 

When the divalent ions, here are of calcium or magnesium, as in hard water, they are sufficiently com-plexed ( sequestered ) by the EDTA" " ligands to render the water softer. ... 

A commercial water softener, (o) The calcium and magnesium ions of hard water are trapped in an ion-exchange resin or a zeolite and are replaced by sodium ions. 

Sodium carbonate is soluble, but calcium carbonate and magnesium carbonate are not (see the solubility rules in Table 4.1). Consequently, the carbonate anions react with dissolved Mg and Ca ions in hard water to form solids that precipitate from (or come out oO solution ... 

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