Hi, For school we are currently working with heterogeneous equilibria. I am given a salt that will be solved in water and I have to calculate the concentrations of the ions. I have to use the solubility product for this. In the Netherlands we are provided with a reference book that has all common values and constants of physics and chemistry in it. I have both the old 5th edition and newest 6th edition of this reference book, which is the only one we are allowed to use in exams. So I look up the Ksp for calcium fluoride. The 6th edition tells me 3,5 * 10^-11. After having calculated the concenstrations, it turns out my answers were wrong. In my answers booklet a value of 1,5*10^-11 was used for the Ksp instead of 3,5. I knew my chemistry book is old, so I checked on the 5th edition for the chemistry references. And here it told me a value of 1,5*10^-11... Okay, obviously my old chemistry book was matched up with the older reference book. But still, why was it changed? I got confused and I checked on the internet and I am seeing different values of the salt everywhere... 3,9*10^-11, 5,9*10^-9... I mean, how can a constant of physics and chemistry not be clear? Am I missing something here? I checked for other salts and I am finding very different Ksp's for them too. Most match up between my 5th and 6th edition reference books and the internet as well, but some of them are completely different everywhere!