Materials: burette, conical flask, ring clamp and stand, 25cm3 of O.O2M EDTA solution, 50 cm3 of Vittel, Contrex and tap water, 12 cm3 of pH 10 buffer solution, 2cm3 of Murexide indicator
Variables
Independent Variables: the amount of EDTA solution needed to change the color of the indicator, the time needed to change the color of the indicator
Dependent variables: the concentration of magnesium and calcium ions in water
Procedure
- add 25cm3 of EDTA into a burette.
- check for air bubbles and leaks
- add 25cm3 of vittel into a conical flask
- Add 2cm3 of pH 10 buffer solution into the conical flask.
- Add 2 drops of Murexide indicator into the conical flask.
- Open the tap of the burette.
- Close the tap if the color change is observed.
- Measure the volume of EDTA solution need ed to change the color of Murexide indicator.
- Record the result.
- Repeat 1- 9 using tap water and Contrex.
- Repeat all the experiments again.
Data Collection
The volume of EDTA needed to change the color of the Murexide indicator
Hypothesis
My results support my hypothesis. Contrex needs the most volume of 0.02mol of EDTA solution to change the color of the Murexide indicator. This is because it has the hightest concentration of Ca2+ and Mg2+ ions. The indicator will change color when all of the Ca+2 and Mg+2 ions have reacted. The reactions of the metal ions are:
Ca+2 + EDTA-2 -----> CaEDTA
Mg+2 + EDTA-2 -----> MgEDTA
For vittel, less volume of 0.02mol EDTA solution is needed as it is less mineralized. Tap water needs the least volume of 0.02mol of EDTA solution because it is not highly mineralized. This is because too much calcium in water can lead to build up that clogs pipes and causes health issues so tap water is softened.
