Heterogeneous ion solution I am a college student and for my chemistry of solutions class, I had a lab where we had to titrate orange juice to check the calcium content. However, the experimental results are 20% off the labelled calcium content, and in my report I have to provide a "Tentative explanation of the discrepancy." 

Is it possible that the orange juice was not completely homogeneous? What I mean is that maybe some of the calcium and other 2+ ions were not well mixed and there were more/less in our sample. Is that possible or are ions always equally dispersed throughout the solvent when in solution?
The calcium amount may change from one fruit to the next one, or from one day to another one, or from one field to another one. 20 % is not a significant difference between such a measurement and another one. And this may happen for any constituant, not specially for calcium.