Determination of the total hardness of water of the drinking water in

Elizade UniversityAdewumi Ezekiel

Computer science

Purpose To determine the “total hardness” of drinking

water in Elizade University using Complexometric titration.

To learn and practice quantitative techniques for determining the concentrations of solutions.

IntroductionWater is said to be “hard” when it contains Ca2+ and Mg2+ ions. These ions react with soap to form an insoluble substance called “soap scum”.

WaterDrinking

Hard water is better for drinking because it contains minerals

WaterCleaning

Soft water is better for cleaning because it doesn’t form scum with soap

WaterHardness of water is a measure of the total

concentration of the calcium and magnesium ions expressed as calcium carbonate.

There are two types of hardness 1. Temporary hardness 2. Permanent hardness Temporary Hardness is due to the presence of

bicarbonates of calcium and magnesium. It can be easily removed by boiling.

Permanent Hardness is due to the presence of chlorides and sulphates of calcium and magnesium. This type of hardness cannot be removed by boiling.

WaterHardness of waterCa2+ and Mg2+ ions along with other metal ions

such as Fe3+ and Pb2+ can be removed from hard water by the addition of EDTA (ethylenediaminetetraacetic acid).

EDTA has a greater affinity for Ca2+ and Mg2+

when it is in the form of the dihydrogen anion H2EDTA2-. This is the ionic form of EDTA at pH 10

Safety Considerations

Keep the pH 10 buffer in the hood. Avoid breathing ammonia vapours from the buffer.

Eriochrome Black T will stain skin and clothes.

All waste materials can be safely rinsed down the sink.

Experimental DetailsStep by step discussion

Apparatus

Reagents 1. Buffer (pH 10): mixture of ammonia and

ammonium chloride solutions in water. 2. EDTA (Disodium Salt of EDTA) for precise end

point. 3. Erichrome Black T.

Solution PreparationpH 10 buffer

As a rule of thumb,The higher the pH (more basic solution), the

sharper the endpointThe higher the formation of constant the lower

the minimum pH

Using apparatus

Clean the apparatus with a brush, water, and a small amount of detergent. Rinse it twice with water. Be sure to drain water through the tip

Rinse the apparatus again with two 10 mL portions of the titrant (EDTA in this experiment).

Experiment

I added a 50ml sample of tap water (cafe,hostel,lab)and 5ml of buffer solution, and a pinch of Erichrome BlackT as the indicator into the cornical flask.

Therefore titrate with EDTA from a 50ml burette

I noted when the color changes from red to blue. Repeated the titration two more times to get the accurate measurement of the total of Mg2+ and ca2+concentration in experiment.

Readings Trial 1 Trial 2 Trial 3

Initial(ml) 0.00 0.00 0.00

Final(ml) 3.90 4.10 3.90

Net volume(ml)

3.90 4.10 4.10

Hostel

Average volume of titrant=4.10ml

LaboratoryReadings Trial 1 Trial 2 Trial 3

Initial (ml) 0.00 0.00 0.00

Final(ml) 4.30 4.00 4.00

Net volume(ml)

4.30 4.00 4.00

Average volume of titrant= 4.00ml

Cafeteria

Readings Trial 1 Trial 2 Trial 3

Initial( ml) 0.00 0.00 0.00

Final(ml) 4.20 4.20 4.70

Net Volume(ml)

4.20 4.20 4.70

Average volume of titrant=4.20ml

Total water hardness of the water samples Hostel

cafeteria

laboratory

Total water hardness (mg/l) = average title value ✕ 20.0

82.0 84.0 80.0

INTERPRETATION OF RESULTS The Total Hardness of the samples (hostel, café, and lab) of drinking water are 82 mg/L,84 mg/l and 80mg/l respectively showing that they are moderately hard.

Conclusion

The total water hardness of the hostel, cafe, and laboratory samples was determined using complexometric titration. The total hardness was determined by using the equation total water hardness as CaCO3 (mg/L) = (titrant volume) ✕ 20.0 respectively. As expected, drinking water from different sources are different. The difference between the samples of the drinking water on the Elizade university campus is not significantly different but likely indicating that they come from the same source without further filtration but no harm involved but since the hardness hasn’t exceeded 250 mg/l no harm involved in any way but in this case the water is moderately hard and it might be freshwater cause the Total hardness in freshwater is usually in the range of 15 to 375 mg/L as CaCO3

Referenceswww.academia.eduwww.slideshare.netwww.titrations.infowww.google.com