Estimation of total hardness and calcium hardness in water sample

 ESTIMATION OF TOTAL HARDNESS AND CALCIUM HARDNESS IN THE SAMPLE WATER

AIM:- To determine the total hardness, calcium and magnesium hardness in the given sample water.

APPARATUS:- Glassware.

THEORY:- Hardness of water is mainly caused by divalent cations. They are capable of reacting with soap to form precipitates and with certain an ions to form scales. Calcium and magnesium ions are the principal hardness causing ions in natural water, even through irons, manganese, strontium and ferrous can contribute to some extent, ferric and aluminum ions can cause hardness but their solubility at the PH of natural waters are so small that they can be considered as insignificant.

            Hardness in water is derived largely from contact with soil and rocks which leads to the solubilization of limestone and other materials. Hardness is normally expressed as mg/l of CaCo₃. Hard waters are not associated with any health hazards. However, they have comparatively higher dissolved solids and cause problems of left out residues on kitchen utensils and glassware and are unfit for bathing and laundry purposes due to high consumption of soap. Hard waters are unfit for certain industries like textiles and beverages and are not suitable for boiler feed.

Hardness is classified in two ways.

i)                    With respect to the metallic ions and

ii)                  With respect to anions associated with metal ions. Calcium and magnesium are, as mentioned earlier, the principal ions associated with hardness. In some cases, it is necessary to know ca⁺² and mg⁺²  hardness individually. In such cases, total hardness and hardness associated with either calcium (or magnesium) are determined. Then,

Total harness – calcium hardness = magnesium hardness.

            The part of total hardness associated with carbonate and bicarbonate alkalinities present in water is considered as carbonate hardness or temporary hardness, as they can be caused to precipitate by prolonged boiling. Since alkalinity and hardness are expressed as mg/l caco₃, the carbonate alkalinity can be obtained as follows.

Case 1:- When total hardness is greater than alkalinity, then calcium

Hardness = alkalinity, and

Case 2:- When total hardness is greater than or equal to alkalinity then carbonate Hardness = total hardness and non – carbonate hardness = 0

            Non carbonate hardness is also called permanent hardness as they cannot be removed by boiling and are associated with sulphates, chlorides and nitrates anions. Hardness can be measured directly by titration with ethylene diamine tetra acetic acid(EDTA) using eriochrome black T(EBT) as indicator. The EBT reacts with the divalent metallic ions, forming a complex that is red in colour. The EDTA replaces the EBT in the complex and when the replacement is complete, the solution changes from red to blue. This is shown by the reactions shown below.

 __           __                                             __            __

│   Ca++    │              +      EBT       =   │  Ca EBT   │

│                │                                          │                  │  complex. (wire red)

│_ Mg++ _│                                          │_ Mg      __│

 __           __                                                _                _

│ Ca EBT  │                                             │ Ca EDTA │

│                │ Complex + EDTA =           │                  │  complex EBT (pale blue

│_ Mg     _│                                             │  Mg         _│                           endpoint)

RELAVENCE:- Hard waters are not associated with any health hazards. However they have comparatively higher dissolved solids and cause problem of left out residues on kitchen utensils and glassware’s and unfit for bathing and laundry purposes due to high consumption of soap. Hard waters are unfit for certain industries like textiles and beverage and not suitable for boiler use. The permissible limit of total hardness for domestic use is upto 300 ppm. The scale of hardness showing different levels of hardness of water is as follows.

         Range (mg/l)                                          Hardness Level

         

         0-50                                                        Soft

         50-100                                                    Moderately soft

         100-150                                                  Slightly soft

         150-250                                                  Slightly hard

         Above 250                                             Hard

CHEMICAL REAGENTS:-

1. BUFFER 1 (for total hardness): To 50ml distilled water, add 1.179 grams disodium salt of EDTA and 780mg. Mgso₄.7H₂o. To this solution, add 16.9 grams ammonium chloride and 143 ml. concentrated ammonium hydroxide and dilute it to 250ml using distilled water.
2. BUFFER 2 (for calcium hardness):- Dissolve 40 grams NaoH in a small quantity of distilled water and make it to 1 lit.
3. EDTA ( Disodium salt) solution 0.01N:- Dissolve 3.723 grams EDTA (Disodium salt) in distilled water and make it to 1 lit.
4. Standard Hard water(0.01N):- Take 1.0 gram caco3 (calcium carbonate) and dissolve it in 1+1 Hcl. Add 200ml distilled water and boil it for a few minutes. After cooling, add distilled water and make it to 1 lit.
5. Eriochrome Black T(EBT) for total hardness.
6. Muroxide (for calcium hardness)

PROCEDURE:-

1. Standardization of EDTA using standard hard water of 0.01N:- Take 25ml standard hard water and make it to 50 ml by adding distilled. Add 1-2ml buffer (1), so as to adjust the PH above 10. then, add a pinch of EBT indicator. The solution turns to wine red. Titrate the solution with given EDTA solution till the colour turns to pale blue. Note down the volume of EDTA consume, and determine the normality of EDTA using the relation

N₁V₁ = N₂V₂

Where

N₁ = normality of EDTA (unknown)

V₁ = volume of EDTA consumed

N₂ = normality of standard hard water = 0.01

V₂ = volume of standard hard water = 25ml

Adjust the normality of EDTA to 0.01N using the relation N₁V₁ = N₂V₂

2. Determination of total hardness in the sample water:- Take 50ml sample water in a conical flask and add 1-2ml buffer (1) solution. Add a pinch of EBT indicator. The sample turns to wine red. Titrate the sample with 0.01N EDTA till the colour turns to pale blue. Note down the volume of EDTA consumed.
3. Determination of calcium hardness in the sample water:- Take 50ml sample water in a conical flask and add a suitable amount of buffer (2) so as to increase PH to 12-13, add a pinch of muroxide indicator. Titrate with 0.01N EDTA till colour turns to pale purple. Note down the volume of EDTA consumed.

OBSERVATIONS:-

S.No	Burette Readings		Vol. of Titrant used
	Initial	Final

CALCULATIONS:-

Total Hardness in mg/lit as caco₃ =   A * B * 1000

                                                         ml of sample water

Calcium Hardness in mg/lit as caco₃ =        A *  B___

                                                               ml of sample water

where

A = ml of EDTA consumed

B = ml of EDTA equivalent to 1mg of caco₃ = 1

(since 1mg of caco₃ is equivalent to 1ml of 0.01N EDTA)

Magnesium Hardness = Total Hardness – Calcium Hardness.

RESULT:-

Total Hardness             =

Calcium Hardness        =

Magnesium Hardness   =

INTERPRETATION OF RESULTS:-