The student determined the total hardness of drinking water samples from the hostel, cafe, and laboratory at Elizade University using complexometric titration with EDTA. The total hardness was calculated to be 82 mg/L for the hostel sample, 84 mg/L for the cafe sample, and 80 mg/L for the laboratory sample, indicating the water sources were moderately hard. As the differences between samples were small, the water sources were likely the same without additional filtration.

1. Adewumi Ezekiel
Computer science

2. 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.

3. Water 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”.

4. Water
 Drinking
 Hard water is better
for drinking because
it contains minerals

5. Water
 Cleaning
 Soft water is better
for cleaning because
it doesn’t form scum
with soap

6. Water
Hardness 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.

7. Water
 Hardness of water
 Ca2+ 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

8. 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.

9. Step by step discussion

10. Apparatus

11. 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.

12. Solution Preparation
 pH 10 buffer
As a rule of thumb,
 The higher the pH (more basic solution), the
sharper the endpoint
 The higher the formation of constant the lower the
minimum pH

13. 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).

14. Experiment

15. 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.

16. Therefore titrate with EDTA from a
50ml burette

17. 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.

18. 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

19. Laboratory
Readings 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

20. 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

21. 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.

23. 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

24. References
 www.academia.edu
 www.slideshare.net
 www.titrations.info
 www.google.com