Water Hardness & EDTA Titration

Water hardness is largely determined by the concentration of dissolved calcium and magnesium ions. Because EDTA forms complexes with these metal ions, complexometric titration can be used to estimate the hardness of a water sample.

The experiment compared two commercially available mineral waters, Evian and Samdasoo, to examine whether differences in their hardness would be reflected in the amount of EDTA required to reach the endpoint.

If a sample contains a greater concentration of calcium and magnesium ions, more EDTA should be required to bind those ions before the titration reaches its endpoint.

Based on the expected hardness of the two mineral waters, the experiment therefore predicted a measurable difference in EDTA consumption between Evian and Samdasoo.

Samples of Evian and Samdasoo were prepared and titrated using an EDTA solution. The amount of EDTA required to reach the endpoint was recorded and used to calculate the hardness of each sample.

Water type served as the independent variable, while the amount of EDTA required during titration was the primary measured outcome. Other experimental conditions were kept as consistent as possible between trials.

The experiment produced measurable differences between the two samples, but the calculated values did not align cleanly with the hardness expected from the mineral waters.

In particular, the calculated hardness of Samdasoo was much higher than expected. This suggested that the discrepancy could not be interpreted simply as a property of the bottled water itself.

Instead, the unexpected result raised a second question: which part of the experimental procedure may have altered the measurement?

One possible source of error was the preparation of the EDTA solution. Tap water had been used during dilution, meaning that additional dissolved calcium or magnesium ions may have been introduced into the experimental system.

Because EDTA reacts with these ions, contamination during solution preparation could influence the amount of EDTA apparently required during titration and therefore distort the calculated hardness.

Other procedural uncertainties could also contribute to the final measurements, making careful control of reagents and solution preparation especially important.

The purpose of the experiment initially seemed straightforward: compare two types of water and determine how hardness affected EDTA consumption.

But the discrepancy between the measured and expected values made the analysis more important than the numerical result itself. It required tracing the procedure backward and considering where uncontrolled ions could have entered the system.

The experiment reinforced that experimental data should not be accepted simply because a calculation produces a number. A result must also make sense in relation to the method that produced it.