Analysis of Hard Water

Analysis of hard water Introduction Hard water is water that has high mineral content (in contrast with soft water). Hard water has high concentrations of calcium, magnesium and iron ions. These ions are called hardening ion. In low concentrations, these ions are not considered harmful for domestic use, but when present in higher concentrations these ions interfere with the cleansing action of soaps and accelerate the corrosion of steel pipes, especially those carrying hot water Soaps are sodium or potassium salts of higher fatty acids such as stearic acid, C17H35COOH . Soaps such as C17H35COONa+ are very effective cleansing agents so long as they remain soluble in water. They react with Ca2+ and Na2+ ions present in hard water and form an insoluble sticky precipitate of calcium and magnesium salts of fatty acids known as scum and thus interfere in the cleansing action of soap. C17H35COONa+ (aq) + Ca2+ (aq)

C17H35COOCa2+ +2Na+

Hardness of water can be defined as the soap – consuming capacity of water, or the capacity of precipitation of soap as a characteristic property of water that prevents the lathering of soap. It is responsible for the formation of boiler scales on tea kettles and vessels used for heating water. The boiler scale reduces the efficiency of transfer of heat because it is a bad conductor of heat. Formation of boiler scale in the pipes carrying hot water reduces the rate of flow of water in them. On extreme cases due to overheating the boiler or the pipes may break due to overheating. The boiler scale consists of primarily of the carbonates of hardening ions. Ca2+ (aq) + 2HCO3-(aq)

CaCO3(s)+CO2(g)+H2O(l)

The hardening ions enter into water as a result of reaction between slightly acidic rain water and mineral deposits. Ground water becomes hard as it flows through underground lime – stone deposits. The water from the deep wells has higher degree of hardness as compared with water from shallow wells because of greater interaction with the lime – stone deposits.CO2 dissolved in water, makes it slightly acidic and helps in dissolved lime-stone deposits. CO2 (aq) + CaCO3(s) + H2O(l) (aq)

Ca2+ (aq) + 2HCO3-

Types of hard water Hard water can be classified into two: 

Temporary Hard water Permanent Hard water

Temporary hardness Temporary hardness is caused by a combination of calcium ions and bicarbonate ions in the water. it can be removed by boiling the water or by the addition of lime (calcium hydroxide). Boiling promotes the formation of carbonate from bicarbonate and precipitates calcium carbonate out of the solution, leaving water that is softer upon cooling. The following is the equilibrium reaction when calcium carbonate (CaCO3) is dissolved in water. CaCO3(s) + CO2(g) +H2O(l)

Ca 2+ (aq) + 2HCO3-

(aq) Upon heating, less CO2 is able to dissolve into the water. Since there is not enough CO2 around, the reaction cannot proceed from left to right, and therefore the CaCO3 will not dissolve rapidly. Instead, the reaction is forced to the left to re-establish equilibrium, and solid CaCO3 is formed. Boiling the water will remove hardness as long as the solid CaCO3 that participates out is removed. After cooling, if enough time passes, the water will pick up CO2 from the air and the reaction will again proceed from left to right ,allowing the CaCO3 re-dissolve into the water. Permanent hardness Permanent hardness is hardness that cannot be removed by boiling. It is usually caused by the presence of calcium and magnesium sulphates and or chlorides which become more soluble as the temperature rises. Despite the name, permanent hardness can be removed using a water softener or ion exchange column, where the calcium and magnesium ions are exchanged with the sodium ions in the column. Hard water causes scaling, which is the left – over mineral deposits that are formed after the hard water had evaporated .this is also known as

lime scale the scale can clog pipes , ruin water heaters , coat the inside of tea and coffee pots and decrease the life of toilet flushing units. Hardening must be constantly monitored to avoid costly breakdowns in contact with water. Hardness is controlled by the addition of chemicals and by large-scale softening with zeolites (Na2Al2SiO8.xH2O) and ion exchange resins. Effects of hard water These are advantages and disadvantages for people who live in hard water areas. Disadvantages of hard water  It is difficult to form lather with soap.  Scum may form in a reaction with soap thus wasting soap.  Lime scale (a hard crust) forms inside kettles. This wastes energy whenever you boil a kettle.  Hot water pipes fur up. Lime scale starts to coat the inside of the pipes which can eventually can get blocked up. Advantages of hard water  Some people prefer the taste.  Calcium ions in the water are good for children’s teeth and bones.  It helps to reduce heart disease.  A coating of lime scale onside copper pipes or especially old lead pipes sops poisonous salts dissolving into water EFFECTS ON SKIN Some confusion may arise after a first experience with soft water. Hard water does lather well with soap and leaves a “clean feeling”. Soft water lathers better than hard water but leaves a “slippery feeling” on the skin after use with soap. Some providers of water softening equipment claim that the “slippery feeling” after showering in soft water is due to “clean skin” and absence of friction causing soap scum. However, the chemical explanation is that softened water, because of its sodium content, has a much reduced ability to combine with the soap film on the body; therefore, the soap is much more difficult to rinse off. Solution are to use less soap or a synthetic liquid body wash. SOFTENING

It is often considered desirable to soften hard water. This is because the calcium and Magnesium ions block the oil emulsifying action of soap due to the formation of insoluble scum. Large amount of soap have to be used to counteract this. Most modern soaps and detergents contain ingredients that at least partly prevent this effect and detergents are available that are chemically completely unaffected by the hardness. This makes hardness removal/softening an optional rather than a necessary water treatment except possibly in the case of extremely hard water. Where softening is practiced it is often recommended to soften only the water sent to domestic hot water systems so as to prevent damage due to scale formation in water heaters. Another reason for this is to avoid adding sodium or potassium from the softener to cold water taken for human consumption while still providing softening for hot water used in washing and bathing. PROCESS A water softener works on the principle of cation or ion exchange in which hardening ions are exchanged for Sodium or Potassium ions, effectively reducing the concentration of hardness to tolerable levels and thus making the water softer and giving it a smoother feeling. The most economical way to soften household water is with an ion exchange water Softener. This unit uses Sodium Chloride (NaCl) to recharge beads made of the ion exchange resins that exchange hardness mineral ions for sodium ions. Artificial or natural zeolites can also be used. As the hard water passes through the beads, the hardness mineral ions are preferentially absorbed, displacing the sodium ions. This process is called ion exchange. When bead or sodium zeolite has a low concentration of sodium ions left, it is exhausted, and can no longer soften water. The resin is recharged by flushing with salt water. The high excess concentration of sodium ions alter the equilibrium between the ions in solution and the ions held on the surface of the resin, resulting in replacement of the hardness mineral ions on the resin or zeolite with sodium ions. The resulting saltwater and mineral ion solution is then rinsed away, and the resin is ready to start the process all over again. This cycle can be repeated many times. Potassium chloride may also be used to regenerate the resin beads. It exchanges the hardness ions for potassium. It also will exchange naturally occurring sodium for potassium resulting in sodium-free soft water. Some softening processes in industry use the same method, but on a much larger scale. These methods create as enormous amount of salty water that is costly to treat and dispose of.

MEASUREMENT The simple way to determine the hardness of water is the lather/froth test: When agitated, lathers easily in soft water but not in hard water. More exact measurements of hardness can be obtained through a wet titration. Although water hardness usually measures only the total concentrations of Calcium and Magnesium (the two most prevalent, divalent metal ions), iron, Aluminium, and Manganese may also be present at elevated levels in some geographical locations. The degree of hardness in water depends on the extent of hardening ions present in water. The concentration of hardening ions is a water sample is generally expressed as though the hardness is due exclusively to CaCO3. The units or hardness is mg CaCO3/litre which is same as parts per million (ppm) CaCO3.

A General Classification Of Hard Water is given below: Hardness (ppm CaCO3)

Classification

200ppm

Very soft water Soft water Medium hard water Hard water Very hard water

Experiment Aim To determine the hardness of a water sample

Requirements 250ml conical flask , funnel , beaker , burette , pipette. Standard EDTA(Na2H2Y)solution ,buffer solution(pH=10),Erichrome Black T(EBT) indicator

Theory The concentration of hardening ions in water can be determined by a titration technique, the titrant is the disodium salt of ethylenediaminetetraaceticacid

In aqueous solution Na2H2Y dissociates into Na+ and H2Y2- ions.Ca2+ and Mg2+ react with H2Y2- to form stable complexes in a solution having pH of about 10.a buffer solution containing ammonia and ammonium ions is used to maintain the pH of the solution around 10. For the detection of the end point Erichrome Black T (EBT) is used as indicator EBT forms complex ions with Ca2+ and Mg2+, but binds more strongly to Mg2+ ions. Since only a small amount of EBT is added, only a small amount of Mg2+ ions is used in the formation of complex and no Ca2+ ions are used. EBT indicator is sky-blue in solution but its complex with Mg2+ ions, [MgEBT]2+, is wine red Mg2+(aq) + EBT(aq) Sky-blue

[Mg-EBT]2+ (aq) wine red

Thus, during titration when indicator is added to hard water ,the initial colour is wine red. When the titrant is added, H2Y2- complexes with free Ca2+ and Mg2+ present in water and finally removes Mg2+ ions from the [Mg-EBT]2+ complex ions. As a result the colour of the solution from wine red to sky blue. [Mg-EBT]2+ (aq) + H2Y2-(aq) + EBT(aq) Wine red

MgY2- + 2H+(aq) sky blue

It may be mentioned here that for the end point to appear, Mg2+ ions must be present in the solution. Therefore, a small amount of Mg2+ (as same salt) is added to the buffer solution and an equivalent amount of Na2H2Y is also added so that the added Mg2+ ions do not affect the amount of H2Y2- used during titration.

Indicator Erichrome Black T(EBT)

End point Wine red to sky blue colour.

Wine red to sky blue

Procedure  Take about 100ml of the water sample to be analyzed. If the water sample contains suspended impurities, it should be subjected to simple filtration. If the water sample is acidic to litmus, add 1M NH3 drop wise until it becomes basic to litmus.  Rinse the burette with Na2H2Y solution and then fill it with the solution. Record the initial reading.  Pipette out 25.0ml of the given sample of water in the conical flask. Add 1ml of the buffer (pH=10) solution and 2 drops EBT indicator. The colour of the solution becomes wine red at this stage.  Titrate the above solution with standard Na2H2Y solution. At the end point the wine red colour disappears and the solution becomes blue(or purple) in colour. Note the final reading of the

burette. Repeat the titration 3 to 4 times to get a concordant reading.

Observations Morality of the standard Na2H2Y solution =0.01M. Volume of water taken for each titration = 20.0ml.

Burette readings  tap water S no. 1 2 3

Initial reading 0.0 4.4 8.9

Final reading 4.4 8.9ml 13.4ml

Volume of Na2H2Y used 4.4ml 4.5ml 4.5ml

Final reading 6.3 12.7 19.1

Volume of Na2H2Y used 6.3ml 6.4ml 6.4ml

Final reading 79.9 80.0ml 80.0ml

Volume of Na2H2Y used 79.9ml 80.0ml 80.0ml

Concordant readings – 4.5ml  pool water S no Initial reading 1 0.0 2 6.3 3 12.7 Concordant readings – 6.4ml  sea water S no 1 2 3

Initial reading 0.0 0.0 0.0

Concordant readings – 80.0ml

Calculations 

tap water

Let the volume of titrant used be Morality of titrant solution

= 4.5 ml = 0.01M

Moles of titrant used

=MxV 1000 =0.01 x 4.5 1000 = 45 x 10-6

Mass of Na2H2Y 10-6

=

Moles of Ca2+

= 0.01 x 4.5 = 45 x 1000

Mass of equivalent CaCO3 = 45x10-6x102

= 0 .01 x 4.5 x100g 1000 =45x10-4 mg

Mass of CaCO3 per litre = 45 x 10-4 x 1000 20 =50 x 45 x10-4 =225 x 10-3mg/l Hardness = 106

= 225 x 10

-3

x

= 225 x 10 103

-3

x 106

= 225 ppm

Calculations 

Pool water

Let the volume of titrant used be Morality of titrant solution

= 6.4 ml = 0.01M

Moles of titrant used

=MxV 1000 =0.01 x 6.4 1000 = 64x 10-6

Mass of Na2H2Y

=

Moles of Ca2+

= 0.01 x 6.4= 45 x 10-

6

1000 Mass of equivalent CaCO3 64x10-6x102

= 0 .01 x 6.4x100g = 1000 =64x10-4 mg

Mass of CaCO3 per litre = 64 x 10-4 x 1000 20 =50 x 64 x10-4 =320 x 10-3mg/l Hardness = 106

= 320 x 10 = 320x 10 103

-3

-3

x

x 106

= 320 ppm

Calculations  Sea water Let the volume of titrant used be Morality of titrant solution

= 80 ml = 0.01M

Moles of titrant used

=MxV 1000 =0.01 x 80 1000 = 80 x 10-5

Mass of Na2H2Y 10-5

=

Moles of Ca2+

= 0.01 x 80 = 80 x 1000

Mass of equivalent CaCO3 80x10-5x102

= 0 .01 x 80 x100g = 1000 =80x10-3 mg

Mass of CaCO3 per litre = 80 x 10-3 x 1000 20 =50 x 80 x10-3 =4000 x 10-3mg/l Hardness = 106

= 4000 x 10

-3

x

= 4000 x 10

-3

x

106 103

= 4000 ppm

Result The degree of hardness of the following water samples are: Tap water  Pool water  Sea water

-

225ml 320ml 4000ppm

Index

 Certificate  Acknowledgements  Introduction  Aim, theory and procedure  Observations and calculations  Result

Certificate

This is to certify that Eben Mathew of class XII has completed the investigatory project as per the

requirement of CBSE practical work during the year 2010-2011

…………………….. ……………………….. Signature

of

teacher

Signature of examiner

Acknowledgements

I would like to express my gratitude to my teacher Mrs. Rajasree karnavar for providing us with an opportunity to perform this experiment.

I would like to express my appreciation to Mrs. Mary Thomas our lab assistant for her guiding support throughout the experiment.

Lastly a sincere thanks to my partners Rahul Mahajan and Nabeel for the great deal of effort put into this experiment.

Chemistry Project Analysis of hard water

BY: Eben Mathew Clas s: XII-K