What would you do in the following instance?

Question

Suppose u have a water sample that u want to test for hardness. You titrate the sample but find it so hard that even after u have added all the EDTA in the buret , the endpoint is not reached. Aside from continuing to refill the buret time and time again( which, by the way, is not a good analytical technique), what would u do to perform the analysis? Suggest 2 ways to perform the analysis. Please help me in answering this question related to hardness of water. Thanx in advance

Answer 1

First, I would continue titrating by refilling the buret to obtain an estimate of the volume needed for the sample. This estimate can then be used to determine the factor by which to divide the sample.
Say it took 75 mL of EDTA then you would know that a sample of water one half as large as the previous one would take approximately 37.5 mL (well within the range of a 50 mL buret).
Another technique would be to titrate with a higher concentration of EDTA. Double the concentration and the required volume would be 1/2, triple the concentration and the required volume for titration of the sample would be 1/3 as large as the starting concentration.
These may be time consuming procedures but would give better results than refilling the buret, a practice that a lot of introductory chem courses employ to save time.