Group 3

Alano, PamelaAlipio, RianneBorromeo, LorenzDe Leon, Jasen EmilDe Sagun, DavidLunas, Louise DianneSan Luis, Rommel Jr.

Instructor: Engr. Jocelyn BalisnomoExperiment No. 3

ESTIMATION OF THE TOTAL HARDNESS OF A WATER SAMPLE USING EDTA

I. Objectives:

Use a complexometrictitrationto determine the total concentration ofcalcium and magnesiumions in a water sample.

II. Materials:

Laboratory Apparatus:Reagents: Graduated Cylinder Hard Water Sample Spatulas for solid indicator Standardized EDTA solution Aspirator Ammonia Buffer Solution (pH 10) Volumetric Flask Distilled Water Beakers Eriochrome Black T Indicator White Card Erlenmeyer Flask Base Burette Iron Stand Burette Clamp Funnel Wash Bottle Acid Pipette

III. Procedures:

1. Wash the pipette, burette and Erlenmeyer flask with deionise/distilled water. Rinse the burette with the EDTA solution and the pipette with the hard water. 2. Using the funnel, fill the burette with the EDTA solution. Open the tap briefly to fill the part below the tap. Remove the funnel. Adjust the level of the solution to the zero mark. Make sure that the burette is vertical.3. Use the pipette to transfer 50ml of the hard water sample to the conical flask.4. Add 0.03g of the solid indicator to the contents of the flask in the following manner: Add gradually to the flask, swirling each addition. A deep wine red color is obtained.5. Carry out one rough titration to find the approximate end point, followed by a number of accurate titrations until two titres agree to within 0.1ml. At the end point, the color should be dark blue, with no tinge of wine-red color.6. From the data, calculate the total hardness of the water sample.

IV. Computations

A. Preparation of CaCO3 concentration of HCl

CHCl= (37g/100g)(1.18g/1ml)(1000ml/1L)(1mol HCl/36.45g HCl)CHCl = 11.98M

Dilution of HCl:11.98M(V1)=(1M)(12ml)V1=0.99ml of 11.98M HCl needed

Reaction: CaCO3 + HCl ---> Ca+2 +CO2 +H2O +2Cl-

Titer Concentration (CaCO3 solution) 250mg CaCO3 /250ml solution = 1mg CaCO3/ml

B. Preparation of EDTA solution

Titer Concentration (EDTA solution) 1000mg CaCO3 /250ml solution = 4mg EDTA/ml

%MgCl2.6H2O (w/w) = 0.01 = (g MgCl2.6H2O/30g + g MgCl2.6H2O)Mass of MgCl2.6H2O = 0.3 g

C. Standardization of EDTA solution

Reaction: Ca+2+ EDTA-4 ------> CaEDTA-2Aliquot: 25ml of CaCO3 (1mg CaCO3/ml)= 25mg CaCO3

Ammonia Buffer (for NH3):20ml(16.5M)=(Cm)(500ml)Cm=0.66M (150ml)(0.66M)=(16.5M)(V)V=6ml

Indicator: 0.5g /100 ml ethanol)(10ml)= 0.05g

Standardization of EDTA SolutionVolume of EDTA used

V0 = 0.00ml

VF = 19.2 ml

VU = VF V0 = 19.2 ml

Aliquot used: 25.00ml of CaCO3 (1mg CaCO3/ml) = 25.00mg CaCO3 needs 19.2 ml of EDTA Solution

Calculations: (EDTA Titer)ET= 25.00mg CaCO3/19.2 ml EDTA solution = 1.302 mg CaCO3 /ml EDTA

V. Results:

Table of ResultsVolume of the Hard Water Sample (VIVA Mineral Water)50ml

Concentration (Titer) of EDTA solution1.302 mg CaCO3/ml EDTA

1st Titration7.3 ml EDTA

2nd Titration7.2 ml EDTA

3rd Titration7.3 ml EDTA

Concordant Value7.3 ml

TOTAL HARDNESS (mg/L CaCO3) = 7.3ml EDTA ()() = () =Viva Mineral Water (Ca+) concentration = () =

*The Viva Mineral Water claims that its calcium ion concentration (Ca+) in mg/L is 54mg/L or 134.85mg CaCO3/L. Based on our analysis, the estimated CaCO3 result was 190.1 mg/L. We can then conclude that the bottled Viva mineral water is quite harder than they claim it to be.

VI. Answers to Questions:

1. Why is it important that the reaction between the EDTA and the metal ions in solution is (i) rapid and (ii) go to completion?These are general requirements of any titrimetic reaction. If the reaction is not almost instantaneous the colour change of the indicator will lag behind the end point and too large a titre would be recorded. If the reagents do not react completely, no conclusion about the concentration of one of the solutions can be obtained from the volume of it that reacts with a known concentration and volume of the other.

2. The water sample could contain metal ions other than Ca2+ and Mg2+. How would the reliability of the result be affected if this were the case? Suggest two other metal ions that could be present in the water. Since alkali metal ions such as sodium or potassium ions do not complex withedta reagent, the results would be unaffected by their presence in the water sample. If, however, there were, for example, iron or aluminium ions present, the value recorded for total hardness by this method would be expected to be too high.

3. This reagent cannot distinguish between temporary and permanent hardness, List the compounds of calcium and magnesium that cause hardness, and indicate those which cause temporary hardness.MgSO4, MgCl2, Mg(HCO3)2, CaSO4, CaCl2 and Ca(HCO3)2 are the water-soluble compounds of magnesium and calcium that cause hardness. Mg(HCO3)2 and Ca(HCO3)2 cause temporary hardness.

4. Suggest a method of establishing the amount of permanent hardness in a water sample.A known volume of hard water is boiled to precipitate the temporary hardness-causing hydrogencarbonate compounds as carbonates. These are removed by filtration. The filter paper is washed with deionised water. The filtrate is made up to an exact volume with deionised water and the edta titration carried out again. The result is used to calculate the permanent hardness of the water sample.

5. What is the function of the buffer solution?All reactions between metal ions and EDTA are pH dependent. For divalent ions, solutions must be kept basic (buffered) for the reaction to go to completion. Eriochrome black T indicator requires a pH of 8 to 10 for the desired color change.

VII. Conclusion

Determination of Hardness of Water Hard water is due to metal ions(minerals) that are dissolved in the ground water. These minerals include Ca2+, Mg2+, Fe3+, SO42-, and HCO3-. This is due to rain moving through the vast amount of limestone, CaCO3 that occurs in our area to the aquifer. This is why we measure hardness in terms of CaCO3; The concentration of the Ca2+ions is greater than the concentration of any other metal ion in our water. Environmental Levels and Human Exposure

Water

Concentrations of up to 100 mg of calcium per litre are fairly common in natural sources of water; sources containing over 200 mg of calcium per litre are rare. Magnesium salts are soluble, natural water sources typically containing concentrations of up to 10 mg/litre. Such sources rarely contain more than 100 mg of magnesium per litre, and it is usually calcium hardness that predominates. In drinking-water, hardness is in the range 10500 mg of calcium carbonate per litre. Estimated daily intakes of 2.3 and 52.1 mg of magnesium in soft- and hard-water areas, respectively, have been reported, based on adults drinking 2 litres of water per day.

Food

Virtually all foods contain calcium and magnesium, and dietary intake is the principal route of exposure. Typical diets provide about 1000 mg of calcium per day and 200400 mg of magnesium per day. Dairy products are a particularly rich source of calcium, whereas magnesium tends to be associated more with meat and foodstuffs of plant origin. Estimated total exposure and relative contribution of drinking-water. The typical dietary contribution of calcium and magnesium is over 80% of the total daily intake. Of this, approximately 30% of calcium and 35% of magnesium will be absorbed. For calcium and magnesium, the typical contribution from water is 520%.

Effects on HumanThere does not appear to be any convincing evidence that water hardness causes adverse health effects in humans. In contrast, the results of a number of epidemiological studies have suggested that water hardness may protect against disease. However, the available data are inadequate to prove any causal association.