Magnesium ions, soap precipitation

MetaUic ions are precipitated as their hydroxides from aqueous caustic solutions. The reactions of importance in chlor—alkali operations are removal of magnesium as Mg(OH)2 during primary purification and of other impurities for pollution control. Organic acids react with NaOH to form soluble salts. Saponification of esters to form the organic acid salt and an alcohol and internal coupling reactions involve NaOH, as exemplified by reaction with triglycerides to form soap and glycerol,... 

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. 

There are two solutions to soften water that is too hard. First, the water could be filtered to remove all of the calcium and magnesium ions. But this can be very expensive, so most people use a water softener instead. A water softener is a piece of equipment that can be attached to the water pipes that run into a house. This way, all the household water goes through the water softener before going into the other pipes in the house. Inside a water softener are small plastic beads. These beads have sodium ions (Na+) stuck on them. As the water flows over the bed of beads, the magnesium and calcium ions get replaced with the sodium ions. Since sodium is easily dissolved in water, it does not precipitate out in pipes like calcium and magnesium ions do. As a result, no scales form inside the pipes. Sodium ions do not react with soap to form soap scum, either, and they allow the soap to lather properly. 

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). 

Another common precipitation product is soap scum. Soap scum generally floats on water rather than raining out, so it is normally not thought of as a precipitate—but that is a matter of semantics. Scum can form in bathtubs when soap mixes with hard water that is, water that contains calcium and magnesium ions. Water that contains calcium and magnesium ions is called hard because these ions tend to form insoluble precipitates (that is, little rocks) in the water. 

Sodium lauryl sulfate reacts with cationic surfactants, causing loss of activity even in concentrations too low to cause precipitation. Unlike soaps, it is compatible with dilute acids and calcium and magnesium ions. 

For soap to work, its anions must stay in solution. Unfortunately, they tend to precipitate from solution when the water is hard. FFard water is water that contains dissolved calcium ions, Ca, magnesium ions, Mg +, and often iron ions, Fe or Fe. These ions bind strongly to soap anions, causing the soap to precipitate from hard water solutions. 

Originally, the hardness of water was understood to be a measure of the capacity of the water for precipitating soap. Soap is precipitated chiefly by the calcium and magnesium ions commonly present in water but can be precipitated by other polyvalent ions such as aluminum, iron, manganese, strontium, and zinc. 

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. 

Water that contains dissolved calcium and magnesium salts is called hard water. Ordinary soap does not lather well in hard water the soap reacts with the calcium and magnesium ions to form an insoluble greasy scum. However, synthetic soaps, known as detergents, have excellent cleaning qualities and do not form precipitates with hard water. Hard water is also undesirable because it causes scale to form on the walls of water heaters, tea kettles, coffee pots, and steam irons, which greatly reduces their efficiency. 

Soap has been used for over two millennia, as people discovered long ago that soap could be made by heating animal fat together with wood ashes, which contain alkaline substances. Nevertheless, the usefulness of soap is diminished in the presence of water that contains high concentrations of calcium ions (Ca ) or magnesium ions (Mg ). When soap is used with such water, called hard water, a precipitate is formed as a result of the following ion exchange reaction. 

As a result of the solvent properties of water, the naturally occurring Uquid always contains dissolved matoials, particularly ionic substances. Hard water contains certain metal ions, such as Ca and Mg". These ions react with soaps, which are sodium salts of stearic add and similar organic acids, to produce a curdy precipitate of calcium and magnesium salts. This precipitate adheres to clothing and bathtubs (as bathtub ring). Removing Ca " and Mg ions from hard water is referred to as water softening. 

---