posted by tan ni .
1.why must MgCl2.6H20 be added to the EDTA solution?
2. why should EDTA solution be stored to the polyethylene container?
3. why should HCl be added to calcium carbonate solution?
4. why is it necessary to buffer the solution at pH 10 during titration?
Isn't all of this explained in your lab procedure? Or your text? You really don't have enough information for us to answer. You don't explain what you are doing.