Determination permanent hardness

The permanent hardness of a sample of water may be determined as follows. Place 250 mL of the sample of water in a 600 mL beaker and boil gently for 20-30 minutes. Cool and filter it directly into a 250mL graduated flask do not wash the filter paper,... 

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. 

Permanent hardness can also be estimated by the alkalimetric method of Wartha and Pfeifer. A measured volume (200 e.e.) of the water is boiled with 50 c.e. of a mixture of decmormal solutions of sodium carbonate and hydroxide in equal amounts after restoring to the original volume and allowing the solution to settle, the residual alkali is determined by titration with standard acid. As the bicarbonates do not cause any consumption of alkali, there is a direct proportionality between the quantity of alkali which disappears and the total amount of sulphates and chlorides of calcium and magnesium. Sodium carbonate alone does not efficiently precipitate magnesium salts from solution, but precipitation as the hydroxide is complete if excess of sodium hydroxide is present it is for this reasoii that a mixture of sodium carbonate and hydroxide is applied 3 (see also p. 211). 

The methods most widely used in determining the hardness of metals are the static indentation methods. These involve the formation of a permanent indentation in the surface of the material under examination, the hardness being determined by the load and the size of the indentation formed. Because of the importance of indentation methods in hardness measurements a general discussion of the deformation and indentation of plastic materials is given in Chapter 2. 

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. 

There are two types of hardness test static tests that involve the formation of a permanent indentation on the surface of the test material and dynamic tests in which a pendulum is allowed to strike the test material from a known distance. Vickers and Brinell tests, two examples of static methods, are the most commonly used methods for determining the hardness of pharmaceutical materials. In the Brinell test, a steel ball of diameter D is pressed on to the surface of the material, and a load F is applied for 30 sec and then removed. The diameter dj of the indentation produced is measured, and the Brinell Hardness Number (BHN) calculated by... 

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 ... 

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. 

One of the most significant advances in chemical analysis as applied to pharmaceuticals during the last decade is undoubtedly the introduction and development of the complexometric titration. The ability of certain amino-polycarboxylic acids to react stoichiometrically and instantaneously with certain metal ions was first recognised and described by Schwarzenbach in 1945. Later, the same author, together with co-workers, described the first metal indicator, murexide, and then, perhaps the most important of all, Eriochrome Black T (usually referred to in this country as solo-chrome black). This was followed quite shortly by the first description of the now classic use of the complexometric titration for the determination of temporary and permanent hardness in water. It was some time, however, before metal indicators capable of functioning at an acid pH were developed with the availability of such indicators a rapid increase in the application of complexometric titrations took place and there are now few metal ions that are not capable of determination by this means. In the present book reference will be found to the use of complexometric methods for determination of aluminium, bismuth, calcium, copper, iron, lead, magnesium, manganese, mercury and zinc. In addition, indirect methods are described for the determination of certain anions such as fluoride, phosphate and sulphate. 

Determination of Permanent Hardness using a Mixture of Na2CO and NaOH An aliquot of the hard water sample is boiled with a known excess of al kali mixture (Na2C03 + NaOH). This precipitates permanent hardne.ss due to Ca and Mg " ... 

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. 

DETERMINATION OF THE TOTAL HARDNESS (PERMANENT AND TEMPORARY) OF WATER... 

Hardness measures the resistance of a material to a permanent change of shape. That is, the resistance to shear deformation (not the resistance to a volume change). The precursor to a permanent shape change is a temporary elastic shape change, and a shear modulus determines this. Therefore, the first necessity for high hardness is a high shear modulus. 

The optimum cure of such a stock is quoted as 45 mts at 138°C. The above details on optimum cure are related only to natural rubber and do not apply to SBR in which case hardness and modulus continue to increase beyond the optimum cure point. However this gives an insight into the cure state after all of the vulcanizate in general. Tear resistance and cut growth and permanent set, however, have been used to determine the optimum cure of SBR. 

A No known as Diamond Pyramid Hardness. Indcnter is a square-hased diamond pyramid with included angle between faces of 136°. Loads may vary1 from 1 to I 20 kilograms with 10. 30. and 50 kilograms in common use. Hardness is equal to load (kilogramsi divided hy surface area (square millimeter) of the permanent indentation, ll is determined directly from oplical measurements of the diagonals of the indentation, which appear square at Ihe surface of the metal. 

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