Hardness with soap solution

Permanent hardness may be determined in the following manner. A quantity of the water measuring 100 ml is boiled gently for 45 minutes, cooled, and made up to its original volume with cold carbon-dioxide-free water. After mixing well, the precipitated temporary hardness is removed by filtration, and the permanent hardness determined in the filtrate by titration with soap solution. The temporary hardness will be the difference between the total and the permanent hardnesses. 

In this experiment you will prepare temporarily hard water study some of the chemical properties of soft, temporarily hard, and permanently hard water and study various processes available for softening hard water. The hardness of different water samples will be tested quantitatively by determining the volume of soap solution that must be added to a given volume of water in order to obtain a lather. Moreover, hard water will be treated by several methods designed to soften it, and the treated water will be titrated with soap solution to test the effectiveness of the methods. A study of the hardness of water, the action of soaps, and methods for softening water will illustrate characteristic chemical reactions and important differences in solubilities of some compounds of alkali metals and the alkaline earth metals. In addition, you will become familiar with a laboratory preparation for and properties of carbon dioxide gas. 

Wet a hard, flat surface, about 10 cm x 10 cm in area, with the soap solution. 

Sometimes people refer to water as being "hard" or "soft." If someone says water is hard, he means that there are a lot of calcium (Ca2+) or magnesium (Mg2+) ions dissolved in it. Hard water causes several problems. First, it can cause scales to form on the inside of pipes, water heaters, or teakettles. These scales occur when the calcium or magnesium precipitates out of solution and sticks to the insides of pipes. The scales build up and eventually the pipes are completely clogged. Hard water also prevents soap from lathering, and it reacts with soap to leave behind a sticky film commonly called soap scum. 

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. 

Standard experiments with permanently and temporarily hard water. Measure the number of drops of soap solution needed to form a permanent lather in 10 cm3 samples of both types of hard water. Boil both types and allow to cool. Then measure the number of drops of soap solution needed to produce a permanent lather in 10 cm3 samples of the treated samples of hard water. The study can be extended... 

Compare soap and soapless detergents. Add soap solution dropwise with shaking to samples of hard and soft water. Repeat using a soapless detergent. 

Hard water reactions. Place about one-third spatula full of the soap you have prepared in a 50-mL beaker containing 25 mL of water. Warm the beaker with its contents to dissolve the soap. Pour 5 mL of the soap solution into each of five test tubes (nos. 1, 2, 3, 4, and 5). Test no. 1 with 2 drops of a 5% solution of calcium chloride (5% CaCl2), no. 2 with 2 drops of a 5% solution of magnesium chloride (5% MgCl2), no. 3 with 2 drops of a 5% solution of iron(III) chloride (5% FeCl3), and no. 4 with tap water. Tube no. 5 will be used for a basicity test, which will be performed later. Record your observations on the Report Sheet. 

Determination of Hardness.—Hardness, whether temporary or permanent, is conveniently estimated by means of Clark s soap test, which consists m adding from a burette small quantities of standard soap solution (vide infra) to 50 c.c. of water which have been carefully measured out with a pipette into a 250-c.c. bottle. After each addition of soap solution the bottle is vigorously shaken, and the titration is complete when the lather remains unbroken for five minutes after laying the bottle on its side at rest. 

Should the water be so hard that 8 c.c. upwards of soap solution are required, a smaller volume than 50 c.c. should be taken and diluted to tins amount with freshly boiled distilled water. Reference to the table indicates the amount of hardness corresponding to each titration. The total hardness is given by this method. If a second sample of water be boiled and after settling or filtering titrated m a similar manner, the permanent hardness is obtained. Subtraction gives the temporary hardness. 

With the eye dropper, add some soap solution, drop by drop, to test tube No. 1, shaking the tube very hard between drops. Count how many drops are needed to make suds and record the number. To test tube No. 2, add some soap solution in the same manner and count again. To test tube No. 3, add some soap solution in the same way. Take test tube No. 4 from the rack and boil the liquid over the alcohol flame. Add some soap solution after it has cooled, and count the drops needed to form suds. To test tube No. 5 add soap solution only, shake, count the drops, and record the result. To test tube No. 6 add 1 teaspoonful of sodium tetraborate or potassium carbonate, then add some soap... 

The presence of salts of calcium or magnesium in solution can be most undesirable in many finishing processes. These salts are responsible for hardness of water and they lead to the formation of insoluble precipitates with soaps which may be deposited on the goods, causing discoloration. Calcium and magnesium compounds are commonly present as sulphates and chlorides. Bicarbonates produce what is known as temporary hardness sulphates and chlorides are the cause of permanent hardness. 

The most important characteristic of hard water is its reaction with soap. If distilled or soft water be shaken with a solution of soap a lather or foam is formed immediately. If, however, a dilute solution of soap be added drop by drop to some hard water in a bottle which is stoppered and shaken after each addition, it will be found that no lather is formed at first. The water, at the same time, assumes a turbidity owing to the formation of an insoluble precipitate. Finally, after sufficient soap has been added, a lather will appear. Soaps are sodium salts of fatty acids of high molecular weight, such as sodium oleate CuHggCOONa. The salts of sodium are soluble in water, but those of calcium and magnesium are not and, in hard water, the ions of these elements displace the sodium, giving precipitates of their insoluble fatty acid salts ... 

Total hardness is the faetor which is most commonly required in routine testing. The simplest method is based on titration with a standard soap solution whieh depends upon the reaetion ... 

It may be mentioned that the stearate above i 5 normal is hardly a solution, 1 5N sodium stearate at 90° is a viscid gum On the other hand, 2 oN potassium laurate solution with a similarly shaped curve is a clear oily liquid The form of the curve is thus due to the constituents in the system and is not due to mechanical effects, eg gel formation, skins on the surface, or other changes of state The effect is also not due to hystensis, as is the case m the dehydration of certain gels, for it is independent of the age or method of preparation of the soap solution or whether water may have been previously added or taken away It will be pointed out later that the existence of the minimum m the boiling pomt nse is due to dehydration of the colloidal constituents, thereby releasing a quantity of solvent which effectively dilutes the solution and thus produces a diminished nse in the boiling point Were it not for this, the boiling point would nse steadily all the way with increase m concentration... 

Adjust the castile soap solution so that 2.4 mL of it will give a permanent lather with 40 mL of solution (b). When adjusted, 2.4 mL of soap solution is equivalent to 220 parts per million of hardness (as CaCOj) for a 40 mL sample. See also Soap solution. Brucke s reagent (protein precipitation). See Potassium iodide-mercuric iodide. 

Soap solution (reagent for hardness in water). Dissolve 100 g of dry castUe soap in 1 L of 80% alcohol (5 parts alcohol to 1 part water). AUow to stand several days and dUute with 70% to 80% alcohol untU 6.4 mb produces a permanent lather with 20 mb of standard calcium solution. The latter solution is made by dissolving 0.2 g of CaCO in a small amount of dUute HCl, evaporating to dryness and making up to 1 L. 

To determine the hardness, 70 c.c. of the water to be tested are placed in a glass-stoppered bottle of 250 c.c. capacity, and the soap solution gradually added from a burette. After each addition of soap solution the bottle is shaken, and alloAved to lie upon its side five minutes. This is continued until at the end of five minutes a kather remains upon the surface of the liquid in the bottle. At this time the haidness is indicated by the number of c.c. of soap solution added, minus one. If more than 16 c.c. of soap solution are added the liquid in the bottle must be diluted with 70 c.c. of distilled water. 

Hardness of water is usually expressed by assuming that all the hardness is due to dissolved calcium carbonate, which is present as ions. It can be estimated by titration with a standard soap solution or with edta. See also water softening. 

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