DETERMINATION OF HARDNESS OF WELL WATER SUPPLY IN ENUGU METROPOLIS

CHAPTER TWO

1. LITERATURE REVIEW

2.1 CONCEPT OF WATER

Water, common name applied to the liquid state of the hydrogen-oxygen compound H2O. The ancient philosophers regarded water as a basic element typifying all liquid substances. Scientists did not discard that view until the latter half of the 18th century. In 1781 the British chemist Henry Cavendish synthesized water by detonating a mixture of hydrogen and air. However, the results of his experiments were not clearly interpreted until two years later, when the French chemist Antoine Laurent Lavoisier proved that water was not an element but a compound of oxygen and hydrogen. In a scientific paper presented in 1804, the French chemist Joseph Louis Gay-Lussac and the German naturalist Alexander von Humboldt demonstrated jointly that water consisted of two volumes of hydrogen to one of oxygen, as expressed by the present-day formula H2O.

Almost all the hydrogen in water has an atomic weight of 1. The American chemist Harold Clayton Urey discovered in 1932 the presence in water of a small amount (1 part in 6000) of so-called heavy water, or deuterium oxide (D2O); deuterium is the hydrogen isotope with an atomic weight of 2. In 1951 the American chemist Aristid Grosse discovered that naturally occurring water contains also minute traces of tritium oxide (T2O); tritium is the hydrogen isotope with an atomic weight of 3.

2.2PROPERTIES OF WATER (PURE)

Pure water is an odorless, tasteless liquid. It has a bluish tint, which may be detected, however, only in layers of considerable depth. Under standard atmospheric pressure (760 mm of mercury, or 760 torr); the freezing point of water is 0° C (32° F) and its boiling point is 100° C (212° F). Water attains its maximum density at a temperature of 4° C (39° F) and expands upon freezing. Like most other liquids, water can exist in a supercooled state; that is, it may remain a liquid although its temperature is below its freezing point. Water can easily be cooled to about -25° C (-13° F) without freezing, either under laboratory conditions or in the atmosphere itself. Supercooled water will freeze if it is disturbed, if the temperature is lowered further, or if an ice crystal or other particle is added to it. Its physical properties are used as standards to define the calorie and specific and latent heat and in the metric system for the original definition of the unit of mass, the gram

2.3OCCURRENCE OF WATER

Water is the only substance that occurs at ordinary temperatures in all three states of matter, that is, as a solid, a liquid, and a gas. As a solid, or ice, it is found as glaciers and ice caps, on water surfaces in winter, as snow, hail, and frost, and as clouds formed of ice crystals. It occurs in the liquid state as rain clouds formed of water droplets, and on vegetation as dew; in addition, it covers three-quarters of the surface of the earth in the form of swamps, lakes, rivers, and oceans. As gas, or water vapor, it occurs as fog, steam, and clouds. Atmospheric vapor is measured in terms of relative humidity, which is the ratio of the quantity of vapor actually present to the greatest amount possible at a given temperature.

Water occurs as moisture in the upper portion of the soil profile, in which it is held by capillary action to the particles of soil. In this state, it is called bound water and has different characteristics from free water. Under the influence of gravity, water accumulates in rock interstices beneath the surface of the earth as a vast groundwater reservoir supplying wells and springs and sustaining the flow of some streams during periods of drought

2.4FUNCTIONS OF WATER

According to Ikeyi, (2007) water is the predominate chemical component of living organisms. Its unique physical properties are derived from water dipolar structures and capacity to form hydrogen bond.

Water is the major constitutent of living matter. From 50 to 90 percent of the weight of living organisms is water. Protoplasm, the basic material of living cells, consists of a solution in water of fats, carbohydrates, proteins, salts, and similar chemicals. Water acts as a solvent, transporting, combining, and chemically breaking down these substances. Blood in animals and sap in plants consist largely of water and serve to transport food and remove waste material. Water also plays a key role in the metabolic breakdown of such essential molecules as proteins and carbohydrates. This process, called hydrolysis, goes on continually in living cells.

The human body consists mostly of water about 90%. Which forms an essential part of all body cells and fluid eg. Blood. Water is a universal solvent, it has the ability to dissolve a wide range of organic and inorganic molecule, it enters into reaction and acts solvent for many ions and molecules. The manner in which water interacts with solvented biomoleculor in fluencies or changes the structures of the biomolecular.

2.5CHEMICAL PROPERTIES OF WATER

Water is one of the best-known ionizing agents. Because most substances are somewhat soluble in water, it is frequently called the universal solvent. Water combines with certain salts to form hydrates. It reacts with metal oxides to form acids. It acts as a catalyst in many important chemical reactions.

2.6STRUCTURE OF THE MOLECULE

A water molecule consists of an oxygen atom and two hydrogen atoms, which are attached at an angle of 105°. Not shown are two pairs of electrons on the bottom that form a similar angle in a plane perpendicular to this view. This asymmetrical arrangement accounts for the many unusual properties of water, such as the fact that it expands when it freezes

1. Water is a dipole – ie a molecule with electrical charge distributed asymmetrical about its structure.
2. Water is a strong dipole and has a high dielectric constant, about 7.85. the dielectric constant enable water to dissolve large quantity of charged compound e.g salts.
3. Water forms hydrogen bonding. This is because of its unshielded hydrogen nucleus covalently bond to an election, with drawing oxygen.

Thus, water interacts through hydrogen bonding, this hydrogen bonding influences physical properties of water and accounts for its high viscosity, surface tensions, boiling points etc. this bond is relatively weak and transient. It also enables water to interact and dissolve many organic molecules that contain functional group, which can participate in hydrogen bonding etc. Aldehydes, ketnoes, alcohols amides etc

Hydrogen Bonding between water and an Alcohol

2.7WATER COMPOSITION

Because of its capacity to dissolve numerous substances in large amounts, pure water rarely occurs in nature. During condensation and precipitation, rain or snow absorbs from the atmosphere varying amounts of carbon dioxide and other gases, as well as traces of organic and inorganic material. In addition, precipitation carries radioactive fallout to the earth's surface.

In its movement on and through the earth's crust, water reacts with minerals in the soil and rocks. The principal dissolved constituents of surface and groundwater are sulfates, chlorides, and bicarbonates of sodium and potassium and the oxides of calcium and magnesium. Surface waters may also contain domestic sewage and industrial wastes. Groundwaters from shallow wells may contain large quantities of nitrogen compounds and chlorides derived from human and animal wastes. Waters from deep wells generally contain only minerals in solution. Almost all supplies of natural drinking water contain flourides in varying amounts. The proper proportion of flourides in drinking water has been found to reduce tooth decay.

Seawater contains, in addition to concentrated amounts of sodium chloride, or salt, many other soluble compounds, as the impure waters of rivers and streams are constantly feeding the oceans. At the same time, pure water is continually lost by the process of evaporation, and as a result the proportion of the impurities that give the oceans their saline character is increased.

2.8HARDNESS OF WELL WATER

Hardness of well water: This is water which will not readily form lather with soap. The effects of this can be seen in everyday life it is different to wash with hard water yet it is wash in rain water.

Hardness is more noticeable in water trickling across and through the ground, dissolving various amounts of chemical compounds like calcium or magnesium tetraoxosulphate (vi) and calcium hydrogen trioxocarbonate (vi). These salts react chemically with soap and the hard water cannot form lather.

The cleaning power of the soap destroyed and a dirty scum is produced.

2 mast(aq)+ Caso4(cq) Na2S04(aq) + Cast2(s)

The dissolved salts in hard water normally react with the soap molecules which are sodium Octadocanote.

2.9 CAUSES OF HARDNESS OF WATER

Hardness of water is caused by the higher percentage of dissolved solid matter which it contains e.g calcium or magnesium tetraoxosulphate (vi) and calcium hydrogen trioxosulphate (iv). According to Ejeogo.C. (2000) hardness of water is also caused when two well water meets underground through soil texture and soil PH.

2.10 TYPES OF HARDNESS OF WATER

There are two types of hardness of water. They ie Temporary hardness and permanent hardness.

2.10.1TEMPORARY HARDNESS

Temporary hardness is the type of hardness that can be removed by boiling. It is caused by the presence of either calcium hydrogen troxocabonate (iv) (Ca(Hc02)2 or mangnesium hydrogen trioxocarbonate (iv) (mg (H­c03)3).

Temporary hardness I sproduced when rain water containing dissolved carbon (iv) oxide flows over or through deposit of

limestone or chalk. The rain water is trioxo carbonate (iv) acid.

H2Co3(aq) + ca co3 Ca (H.C.O3)2

Trioxocarbonate limestone calium hydrogen

(iv) Acid or Chalk Trioxocabonate (iv)

2.10.2 PERMANENT HARDNESS

Permanent hardness is the type of hardness which cannot be removed by boiling. It is caused by the presence of calcium and magnesium ions in the form of soluble tretraoxosulphate (iv) and chlorides.

According to Blake (1999-06)” hard water can be prepared when gypsu or anhydrous calcium tretraoxosulphate (iv) is added to water in a flask. Shake and allow to stand, Decant off the clear liquid which is permanent hard water. In two cases distilled water is used because ordinary well water contained degree of hardness.

2.11 SOFTENING OF HARD WATER

1. These soluble hydrogen trioxocarbonate (iv) are decomposed by boiling to form insoluble trioxocarbonate (iv) which cannot cause hardness because the calcium trioxocarbonate (iv) formed brings calcium ions out of the solution as precipitate.

Once the calcium ions are out of solution, the soap that is added to the water will be available for the formation of lather.

Ca(Hc03)2(aq) Caco3(s) + (02(g)

Soluble insoluble

The same thing happens with mg (Hc03)2

1. Temporal hardness can also be removed by the addition of calculated amount of slaked time (Ca (OH2).

This removes temporal hardness by converting either the calcium hydrogen trioxocarbonate (iv) or magnesium hydrogen trioxocarbonate (iv) to their insoluble trioxocarbonate (iv) ie CaC03 or mgc03

Ca(Hc03)2 + Ca(OH) Caco3 + H20

Mg(Hc03)2 + Ca(OH)2 2mgc03 + 2H20

i.e permutit process.

1. Another method of removing temporary hardness is by addition of sodium trioxocarbonate (iv). This method can also remove permanent hardness.

Na2c03(aq) + Ca(Hco3)2(aq) NaHco3(aq) + Cac03(s)

1. Distillation: Distillation will remove both types of hardness because all the ions are left behind when the water rapour distills.

Distillation is a rarely used because it is expensive to carry out on a large scale. Permanent hardness of water can also be removed by:

1. Addition of washing soda (Na2c03(s) + Na2s04). The addition of washing soda removes the calcium or magnesium ions as the insoluble calcium and magnesium trioxocarbonate (iv).
2. Permanent method of softening water one large scale.

Many water softening is sold for domestic work on this principle. Permatit is a complex substance (hydrated sodium aluminum trioxosiciate (iv)) commonly called a Zcolite. (Na2 YCY. = AL2 Si203. X H20).

When a dissolved calcium salt runs over it ions exchange will occur, that is,the sodium ions will go into solution while the unwanted calcium or magnesium ions takes their place in the complex salt.

Calcium trioxosulphate + sodium zeolite

Soluble permutit

Calcium zeolite + sodium tetraioxosulphate (iv)

Insoluble soluble

C

(insoluble) (soluble)

1. The addition of caustic soda can also remove the calcium or magnesium ions as the insoluble calcium and magnesium hydroxide respectively.

2.12 EFFECTS OF HARD WATER

2.12.1 EFFECT ON MATERIALS

Carbonate hardness is the most common. It is responsible for deposition of calcium carbonate scale in well water and other equipment Anon. (2013).

In addition calcium carbonate produces carbonate (iv) oxide, resulting from this reaction can combine with water to give carbonate acid which causes corrosion of ion or steel equipments.

Non-carbonate hardness is the culprit in forming soap which is unpleasant. Furry of kettles and boilers is a result of boiling hard water, when they are used to boil hard water for some time, the inner surface becomes coated with a white far-like layer. Shimizu, T (2004) this layer is due to the gradual deposition of calcium hydrogen trioxocarbonate (iv).

Stalagmites and stalactites are also as a result of decomposition of hard water calcium trioxocarbonate (iv) structures growing down wards from the roof is known as stalactites while the one growing upwards from the floor is known as stalagmite, commenges (2003).

2.12.2 HEALTH EFFECT OF HARD WATER CONSUMPTION

Finding show that people that are taking hard water suffer less from heart disease than these taking soft water because the calcium and magnesium in hard water reduces the risk of heart attacks and stroke. Also adequate calcium and magnesium in hard water are instruments in lowering blood pleasure and cancer mortality rate. Commenges (2003).

Furthermore, calcium and magnesium is needed in the diet of young children and pregnant women because it helps to develop strong bones and teeth. Rylander .V. (2010)

2.12.3 EFFECT ON AQUATIC LIFE

Hard water influences aquatic organisms concerning meter toxicity Soft water membrane permeability in the gills is increased.

Also calcium complete with other ions for binding spots in the gills. Calcium and magnesium in water helps to develop strong shalls in aquatic organism. Pocock (2003). Various calcium compounds may be toxic to aquatic life. The LD50 of rats for calcium arsenate forms is 20mgl kg body weight. Calcium, carbide forms filmable ethyne when it comes in contact with water and is therefore considered as hazardous. (Franisek 2003).

2.13 THE CONCEPT OF EDTA METHOD OF WATER ANALYSIS

Ethylenediaminetracetic acid (EDTA) is the most widely used complexing agent for complaxomatric titration or analysis of water hardness and other applications. EDTA has the wildest application because of its powerful complexing action and commercial availability with severalmeter ions it chelation and

the reagents is called challon) EDTA is also as versene, and it is an aminopoly carbonylic acid containing four carbosyl and amino groups.

EDTA behave like a tatrabasic (tetraprotic) acid dissociating in four stages. It is written as H4Y to its tatraproplytic character. The acid is sparingly soluble in water. So its dixodium salt that is, dihydrogene ethylain diamine acetate (written as Na2 H2Y) that is reactively more soluble and commercially available is used in titrimetric work.

In general, that one mole of complex forming ion react with one mole of the metal ion in each case and two moles of ions are formed. Hence, the dissociation of the resultant of the complex depends on concentration pH. The formation of ion as a reaction product will decrease the pH of solution and the reverse reaction may start taking place. This can be prevented by adding a buffer to regulate the pH of the solution at a desired value. The only condition is that buffer itself should no t take part in the chemical reaction. This is reason why most metal-EDTA titration are carried out in neutral or alkaline solution.

INDICATOR SOLUTION: several indicator are used in complexometric titrations. Since these indicators brightly coloured complexes with most metal ions, these are called meterllochromic indicator. This metal ion indicator is a compound whose colour changes when it bind to a metal ion. For an indicator to be useful, it most bind metal less strongly than EDTA. One of the most widely indicators Erichrome Black T which acts as a triprotic acid and can the reform be represented as acid and can therefore be represented as H3 in. This indicator dissociates in three stages giving H2 In, Hln2- and in3- species which are red, blue and orange respectively.