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CHEM

UNIT – IWATER Q1) What is hard water? Explain with example.A1) Hard Water is water that contains a required quantity of dissolved minerals (like calcium and magnesium) As rainwater falls, it is naturally soft. However, as water flows through the ground and into waterways, it picks up minerals like chalk, lime and mostly calcium and magnesium and becomes hard water. Since hard water contains essential minerals, it is essentially used as drinking water. Not only because of the health benefits, but also the flavor. Water that does not produce lather with soap readily is called hard water. Water hardness is usually measured as calcium hardness in milligrams per liter (mg/l) OR parts per million (ppm) OR in grains per gallon (GPG).For e.g.: sea water, river water, spring water, lake water and well water. Q2) What is soft water? Explain with example.A2) Water that shows the absence of dissolved salts of such metals as magnesium, iron, or calcium, which are known to form insoluble deposits such as appear as scale in boilers or soap curds in bathtubs and laundry equipment, soft water is neither healthy nor desirable to drink. Water that readily produces lather with soap is called soft water.For e.g.: Rain water, distilled water, demineralized water. Q3) Explain impurities in water in brief.A3) Hardness can be defined as a soap consuming capacity of water sample. soaps are sodium salts of fatty acids like oleic acid, palmetic acid and stearic acid. they dissolve readily .in water to form lather due to which it has cleansing property.

But compounds of fatty acids with other metals done dissolve in water.
If water contains other metal ions like calcium and magnesium ions they react with sodium salts of long chain fatty acids to form in soluble soap which we observe as curd.

(calciumstearate)

If water contains other metal ions like calcium and magnesium ions they react with sodium salts of long chain fatty acids to form in soluble soap which we observe as curd

These other metal ions are responsible for the hardness of water most important metal of ions which cause hardness to water are calcium and magnesium ions.

The hardness of water along can be calculated from the amount of calcium and magnesium ions present in water along with bicarbonates, sulphates chlorides and nitrates.

TYPES OF WATER	HARDNESS
Soft	0 – 75
Moderately hard	75 – 150
Hard	150 – 300
Very hard	Above 300

Q4) Explain turbidity in water quality parameters.A4) Turbidity is the cloudiness present in water. It is a measure of the ability of light to pass through water. It is caused by suspended materials such as silt, clay, plankton, organic material, and other particulate materials present in water.Turbidity in drinking water is aesthetically unacceptable, which makes the water look unappetizing. The impact of turbidity can be summarized in the following points:It can increase the cost of water treatment for various uses.The particulates can shelter harmful microorganisms and thereby protect them from the disinfection process.Suspended materials can clog or damage fish gills, decreasing its resistance to diseases, reducing its growth rates, affecting egg and larval maturing, and affecting the efficiency of fish catching method.Suspended particles provide a medium of adsorption for heavy metals such as cadium, lead, chromium, mercury, and many hazardous organic pollutants such as polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), and many types pesticides.The amount of available food is reduced because higher turbidity raises water. Consequently, the concentration of the dissolved oxygen (DO) can be decreased since warm water carries less dissolved oxygen compared to cold water.Turbidity can be measured by an instrument called Nephelo metricturbidi meter, the instrument expresses turbidity in terms of NTU or TU. A TU is equivalent to 1 mg/L of silica in suspension.Turbidity that is more than 5 NTU can be visible to the average person while turbidity in muddy water, it exceeds 100 NTU. Groundwater normally has very low turbidity because of the natural filtration that occurs as the water penetrates through the soil. Q5) What is alkalinity? Explain its determination process.A5) A natural water may be alkaline due to presence of hydroxide bicarbonates and carbonates compound dissolve in water.Hydroxides

OH, NaOHBicarbonates Ca (HCO3)2Carbonates MgCO3, FeCO3 Hydroxides and carbonates and stronger bases than bicarbonates.

When an alkaline water is titrated with a strong acid first all OH get neutralized then all the caco3 – ions are half neutralized + OHCo3- .

Till this stage, ph of mixture decreases to about 8.2 and completion of this stage is indicated by change in color of phenolphthalein.

On continued addition of acid during titration all the HCO3 in the titration mixture (produce by half neutralization of CO3 and present from beginning ) get neutralized and completion of this stage is indicated by methyl orange color change at about3.7 ph.

O ( PH = 8.2 )

+ H+ H2O + CO2 ( PH = 3.7 0)

Procedure :- The alkalineties due to the three type of ions can be easily determined by neutralisation titration.

Take V ml ( generally 25 ml ) of the alkaline water in conical flask and add 2 drops of phenopthalein indicator in it .

Titrate this sample against standard strong acid solution ( x n ) from burette till pin k colour changes to colourless . klet the burette be V 1 ml .

Add few drops of methyl orange indicator into the same titrarting mixture changes to orange .

Note the burette reading as V 2 ml ( from initial ) Calculations :- P = phenolphthalein alkalinity =

= PPM Caco3 equivalent M = methyl orange alkalinity = total alkalinity =

ppm Caco3 equivalent The possible combinatuions of alkalinites in water are:-

Only OH-

Only HCO3-

ONLY CO3-

OH- and CO3 – Togther Q6) Explain dissolved oxygen. A6) Adequate dissolved oxygen concentrations are critical during all phases of striped bass and hybrid culture. Low dissolved oxygen concentrations can result in slower growth and induce the stress response predisposing the animals to infectious disease. Monitoring of dissolved oxygen concentrations is complicated by the rate at which they can change. In heavily stocked raceways, tanks, or flow-through systems, for example, an interruption of oxygenation may result in critically low dissolved oxygen concentrations within minutes due to consumption by the culture animals. Management of dissolved oxygen concentrations in ponds must also consider the daily rhythms of concentrations characteristic of ponds. Striped bass and its hybrids have different dissolved oxygen requirements at different stages in their lives. Striped bass also appear to require higher concentrations of dissolved oxygen relative to other temperate species. Generally, dissolved oxygen concentrations should be maintained as close to saturation as possible for best survival and growth. Q7) Explain temporary hardness.A7) Temporary hardness ( carbonate) :-

When water containing calcium and magnesium bicarbonates is heated , bicarbonate decompose and from insoluble carbonate and form hydroxide.

On filtering such water , soft water is obtained.

The hardness which can be removed by more boiling is referred as ‘temporary hardness ’ or bicorbonate hardness.

Mg Mg + 2 CO

(Bicarbonates)

Q8) Explain carbonate hardness.A8) Like all carbonate and bicarbonate, calcium and magnesium carbonate and bicarbonate are alkaline. Then hardness due to the carbonate and bicarbonate is called alkaline hardness or carbonate hardness. The alkalinity can be measures by titration with standard mineral acid using methyl orange and or phenol phthalein as an indicator. As the sulphate and chloride are neutral salts , the hardness caused by presence of calcium and magnesium sulphate , chlorides and nitrates is termed as non alkaline hardness or non carbonate hardness. Q9) Explain EDTA.A9)

Hardness of water can be determined more accurately by EDTA method.

In this method 100ml of water sample is taken in titration flask to this 3ml of buffer an 08 ph 10 is added.

Then it is titrated against 0.01m EDTA using electron black T as an indicator.

At the end point wine red color changes to blue color.

From barrette reading, total hardness of water sample can be calculated using the formula.

1000ml of 1MEDTA = CaCO3 = 100 get CaCO3 6. Suppose barrette reading is xml for 100 ml of water sample. Then for one liter of sample 10x ml EDTA is required.As , 100 ml 1MEDTA = Caco3 = 100 get Caco3 1 ml 0.01 EDTA = 1 mg Caco3 10 x ml 0.01m EDTA = 10 x mg Caco37. Hardness can be expressed as mg of Caco3 present in 10 mg ( 1 liter ) of water i.e. ppm .Hardness of such water sample will be 10 x ppm8. If titration is carried out after boiling the water sample for 30 min the reading will correspond to permanent hardness corresponds to temporary hardness of water sample.9. Ethylene- diamineteracetic acid (EDTA) IS PRACTICALLY Insoluble in water it is represented as H4Y.

INaqueous solution ionises as Na2H2Y

2Na+ + H2Y2-It forms 1:1 complex with Ca++ and Mg++ metal ions present in water sample when indicators is added to water sample colored ( red ) metal indicator complex is formed When this is titrated with EDTA solutionH2Y²- ions react with Ca++ or Mg++ ions from metal indicators complex because these two have more affinity towards EDTA. So more stable metal EDTA complex is formed .at the same time HIn² -ve ions oxygenare set free ( blue ).So, at the end point color changes from red to blue. Q10) Explain the formation of scales.A10) Scale is the hard and strongly adhered coating to the inner surface of boiler and it is a bad conductor of heat. It is the main source of boiler trouble.It is caused due to :-

Decomposition of bicarbonates :-

At high temprature bicarbonates decompose into sticky water insolube material.Ca ( HcO3)2 --------------- CaCO3 + H2O + CO2Mg ( HCo3)2 - - ------------ Mg (Oh)2 + 2CO2 2. Hydrolsis of magnesium salts :- At higher temprature magnesium salts undergo hydrolysis.MgCl2 + 2H2O -------------------- mg ( OH)2 + 2HCl3. Presence of silica :- The source of ssilica is ( form) from sand and filter .silica may be in the form of colloidal particles. And it can be deposite as calcium silicate or magnesium silicate as firmly adhering materials. 4. Decreased solublity of CaSO4 :- CaSO4 has lesser solublity at higher temprature hence at high temprature CaSO4 present in boiler feed water will precipitate as hard scale forming materials.

Q11) Explain Ion Exchange Process. A11) Ion exchange process: Ion exchange technology is a proven method of producing high purity softened and demineralized water. It is used in most industries that require high purity water and to reclaim water from processes. The Ion exchange process involves the exchanging of contaminant ions for Na+ ions in a softening application and H+ and OH- ions in pure water application. Cations and anions can be removed by the cation and anion exchange resins. Resins containing –COOH, SO3H are capable for exchanging their H+ ions to cationic portion of minerals then it is called as cation exchanger while the resins containing –NH2, NHCH3 are capable for exchanging the anionic portion of the minerals then it is termed as anionic exchanger.

On supplying the hard water in first chamber which consists of Ca2+ or Mg2+ then the cation exchanger exchange it with H+ hence the cation exchanger absorbs the Ca2+ ions the left water are free from cations are passed to another chamber by the help of pump this water consists of anions such as Cl or SO4 on sprinkle up of these water at anion exchanger bed then it exchanged the anions and hence release the demineralise water. The absorbed cation and anion are sinked out through the outlet present in chamber. Q12) What is reverse osmosis?A12) Reverse osmosis is a process where the water is separated from the salts in the source water by pressure-driven transport through a membrane. This process uses semi-permeable membrane and applied pressure to preferentially induce water permeation through the membrane while rejecting salts. The RO plant uses less energy than thermal desalination process. This process uses thin-film composite membrane that too comprises of ultra thin aromatic polyamide thin film. The used polyamide film gives the transparent properties while the remaining part provides the mechanical supports. The polyamide films are very dense void free polymer with high surface area allowing for its high permeability. RO desalination plant include source water intake system, pre treatment facilities and high pressure feed pumps, RO membrane trains, energy recovery and desalinated water conditioning system. The intake system may be the open surface water intake or series of seawater beach wells. The pretreatment system may be the screening, chemical conditioning, sedimentation or filtration that totally depends on the used quality water further the filtered water is conveyed by transfer pump from filtrate water storage tank through cartridge filter and into the suction pipe of high pressure RO feed pumps. The cartridge filters are designed in such a manner that can retain 1 to 20 microns particles which remained in the source water after pretreatment. The high pressure feed pumps are designed to deliver the source water to the RO membranes at pressure required for membrane separation of the fresh water from the salts. The actual required feed pressure is site-specific and is mainly determined by the source water salinity and the configuration of the RO system.

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