Magnesium ions, in water

Hardness of water This is caused by the presence of calcium (or magnesium) ions in water, which form a scum with soap and prevent the formation of a lather. There are two types of hardness ... 

Hardness of a water sample is a measure of its capacity to precipitate soap. The presence of calcium and magnesium ions in water essentially contributes to its hardness. Other polyvalent ions, such as aluminum, also cause hardness. Their effect, however, is minimal, because these polyvalent ions occur in water often in complex forms and not as free ions. As a result, they cannot precipitate soap. Although calcium is not the only cation causing hardness, for the sake of convenience, hardness is expressed as mg CaC03/L. Similarly, anions other than carbonate, such as bicarbonate, also cause hardness in water. To distinguish the contributions of such anions from carbonates, hardness is sometimes termed as carbonate hardness and noncarbonate hardness. This can be determined from alkalinity. The relationship is as follows ... 

Hardness Concentration of cations in water that will react with a sodium soap to precipitate an insoluble residue. Total hardness is a measure of the concentration of calcium and magnesium ions in water, usually expressed as mg/L CaC03. Volume 1(10). 

In equation 2, M is the total amount of Mg leached out, V5 volume of the bulk liquid phase, Q time, and K a characteristic constant which is dependent on the concentration of magnesium at the solid surface, total surface area of glass, temperature, and dlffusivity of magnesium ion in water. In logarithmic form. Equation 2 becomes (Cb Mg concentration in bulk liquid phase.)... 

The molar conductance and equivalent conductance of the magnesium ion in water at 25 °C extrapolated to infinite dilution are respectively... 

If S moles of CaCC>3 dissolve in a liter of water, then S moles each of calcium ion and carbonate ion form. With these ion concentrations equal to S, the solubility of CaCC>3 is calculated as 9.3 x 10 5 M. The higher solubility of magnesium carbonate in water, 6.3 x 10 3 M, results from the larger solubility product constant. Nevertheless, both of these carbonate salts are rather insoluble, and the excess carbonate anions provided by the sodium carbonate effectively precipitate the calcium and magnesium ions from solution. 

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. 

The contents of tap water vary among communities. In some areas, the water is hard. Hard water is water that contains large amounts of calcium or magnesium ions. Hardness can be measured in milligrams per liter (mg/L) of calcium or magnesium ions. Hard water makes it difficult to get hair, clothes, and dishes clean. In this lab, you will learn how hard water is softened and how softening water affects its ability to clean. You will also collect, test, and classify local sources of water. 

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. 

Vermiculites are formed by the decomposition of mica. They contain layers of water and magnesium ions in place the potassium ions. When heated to 800°C-1100°C, vermiculite expands because of the conversion of the water to gas. The expanded vermiculite has a low thermal conductivity and density, and is used as a thermal and sound barrier as well as an aggregate in lightweight concrete. It is also used as a moisture-retaining soil conditioner in planting. 

There is some evidence that one potential effect of the release of fluoride is for it to act as an antimicrobial agent. It is known that millimolar concentrations of fluoride ion in water will affect a variety of activities in several types of cell [38]. It does this by denaturing the enzymes. In bacteria, the most important enzyme which can be affected is enolase, and this is responsible for the conversion of 2-P-glycerate to 2-enol pyruvate in the glycolic pathway. Enolase is a magnesium-containing... 

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. 

Self-Test 11.13B The solubility product of magnesium ammonium phosphate, MgNH4P04, is 2.5 X 10 l3. Estimate the molar solubility of the salt, which forms Mg24", NH41, and P043- ions in water. 

Bases that produce hydroxide ions in solution turn phenolphthalein red. Calcium and magnesium produce hydroxide ions in water. The following equations symbolize the reactions ... 

The sheets formed by the apices of the tetrahedra are completed by hydroxyls and magnesium ions in octahedral coordination link the sheets. The one structural arrangement has nine octahedral sites and the other only eight. Both structures have channels on both sides and top and bottom of each ribbon which contains water molecules (zeolitic water). Additional water is bound to the edge of the ribbons and hydroxyls occur in the structure proper. 

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. 

FIGURE 10.2 Concentrations of calcium and magnesium ions in equilibrium with the calcium carbonate and magnesium hydroxide solids, respectively. (From Powell, S. T. (1954). Water Conditioning for Industry. McGraw-Hill, New York. With permission.)... 

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