Introduction:Hard water is water that has high mineral content.

Hard drinking water is generally not harmful to one's health, but can pose serious problems in industrial settings, where water hardness is monitored to avoid costly breakdowns in boilers, cooling towers, and otherequipment that handles water.

Calcium, in the form of the Ca2+ ion, is one of the major inorganic cations, or positive ions, in saltwaterand freshwater. It can originate from the dissociation of salts, such as calcium chloride or calcium sulfate, in water.

CaCl2/MgCl2 (s) → Mg2+/Ca2+ (aq.) + 2Cl– (aq.)

CaSO4/MgSO4 (s) → Mg2+/Ca2+ (aq.) + SO42– (aq.)

Most calcium in surface water comes from streams flowing over limestone, CaCO3, gypsum, CaSO4•2H2O, and other calcium-containing rocks and minerals. Groundwater and underground aquifers leach even higher concentrations of calcium ions from rocks and soil.

The concentration of calcium ions (Ca2+) in freshwater is found in a range of 0 to 100 mg/L, and usually has the highest concentration of any freshwatercation. A level of 50 mg/L is recommended as the upper limit for drinking water. High levels are not considered a health concern; however, levels above 50 mg/L can be problematic due to formation of excess

calcium carbonate deposits in plumbing or in decreased cleansing action of soaps. If the calcium-ion concentration in freshwater drops below 5 mg/L, it can support only sparse plant and animal life, a condition known as oligotrophic. Typical seawater contains Ca2+ levels of about 400 mg/L.

Objective:To measure the hardness in Drinking Water

(Potable water).

Environmental Significance: Scales are formed as inner coating of pipelines

prevents corrosion. Absolutely soft waters are corrosive and dissolve

the metals. More cases of cardio vascular diseases are reported

in soft water areas. Hard water is useful to growth of children due to

the presence of calcium.

Hard waters cause excessive consumption of soap used for cleaning purpose, Sodium soaps react with multivalent metallic cat-ions to form a precipitate, thereby lose their surfactant properties. Lathering doesn’t take place until all hardness ions precipitate out.

This precipitate adheres to surfaces of tubes, sinks, dish washer and may stain clothing.

Scales formed mainly due to carbonate hardness act as insulations and cause enormous loss of fuel in boiler.

Scales deposited mainly due to increase in pH to 9 at which bicarbonates are converted as carbonates and formed in distribution mains reducing their carrying capacity.

Causes:Multivalent Ions

Ca+2, Mg+2, Fe+2, Al+2e.t.c

Types of Hardness in Drinking Water: 1. Calcium Hardness

2. Magnesium Hardness

Mechanism:a.CO2 emissions to atmosphereb.Formation of acid rainc.Dissolution to Ca+2,Mg+2 e.t.c

d.Formation of CaCO3/CaHCO3 Mg as well

Reagents:o Standard Solution EDTA (Ethylene Diaminetetra

acetic acid) o Buffer solution of pH= 10±0.1o EBT Indicator (Eriochrome Black T Indicator)o Water Sample

PRINCIPLE: The method is based on the reaction of heavy metal

ions and alkaline earth metal ions (mostly Ca+2 and Mg+2). The sample is titrated with EDTA solution of known concentration until the initially obtained wine red color of the solution has turned to sky blue color.

The titration is carried out at a pH of 10, in a NH3/NH4+ buffer, which keeps the EDTA (H4Y) mainly in theform HY3– , where it complexes the Group 2 ions very well but does not tend to react as readily with other cations such as Fe3+ that might be present as impuritiesin the water. Taking H4Y and H3In as the formulas for EDTA and Eriochrome Black T, respectively, the equations for the reactions which occur during the titration are:

Titration reaction:

HY3– (aq.) + Ca2+ (aq.) ––→ CaY2– (aq.) + H+ (aq.)

(also for Mg2+)

End point reaction:

HY3– (aq.) + MgIn- (aq.) ––→ MgY2– (aq.) + HIn2– (aq.)

Wine red Sky blue

Materials and Equipment: Burette with Burette stand and porcelain title. Pipettes with elongated tips. Pipette bulb Conical Flask Graduated cylinders Standard flask Wash Bottle Beaker

Procedure: Take 50 ml sample in flask. Add 2ml buffer solution to it. Add 2 drops of EBT indicator (Eriochrome Black T Indicator).

Fill burette with 0.01 M EDTA solution (Ethylene Diaminetetra acetic acid).

Start titration against EDTA solution. Stop titration at end point (Red to Blue). Note reading of EDTA volume used.

Repeat the procedure for distilled water i.e.titrate distilled water against EDTA solution.

Calculations:Hardness (mg/L as CaCO3) = A×B×1000/vol. of sample

where

A = vol. of EDTA used for sample – Vol. of EDTA for DW

B = Weight of CaCO3 = 1ml of EDTA used

So,

Here B = 1

A = 17.2 – 0.3

= 16.9

Hardness = A×B×1000/vol. of sample

= 16.9×1×1000/50

= 1690 (mg/L as CaCO3)

Results:Hardness = 1690 (mg/L as CaCO3) (Very Hard) Discussion:

From the results of the experiment, it is clear that hardness is 1690 (mg/L as CaCO3) which is above 300 so this is very hard water. Hard drinking water is generally not harmful to one's health, but can pose serious problems in industrial settings, where water hardness is monitored to avoid costly breakdowns in boilers, cooling towers, and other equipment that handles water.

The degree of hardness consumers consider objectionable depends on the degree of hardness to which consumers have become accustomed, as described here:

Water Hardness (mg/Las CaCO3)

Designation

0-75 Soft75-150 Moderate150-300 Hard

Above 300 Very Hard

Precaution: Here we are handling ammonia solution so necessary

precaution should be taken for preventing the inhalation.

It causes irritation if inhaled. Do not pipette out the buffer solution using either

measuring cylinder, automatic pipette (or) pipette with a sucker.

Always store EDTA solution and buffer solution in aplastic or resistant glass container.

Discard the buffer solution if it is turbid or if it is stored for a very long period.