This reminds me of that topic where I got into trouble suggesting to a beginning chem student that NaCl was slightly basic:http://www.chemicalforums.com/index.php?topic=35427.msg135549#msg135549
The best answer is that CaCl2
is neither basic nor acidic (it's a salt).
If you were pressed to explain why the CaCl2
solution would be "slightly basic" then you can "rationalize it" I suppose by the fact that for every one calcium ion that is released you release two chloride ions. These chloride ions are VERY weakly basic and so they can liberate OH-
ions to some extent. The problem there as before is that Cl-
is simply very weak. So much so that the acidic byproduct of the reaction of Ca2+
with water actually competes with it. In fact, you can argue as Borek did before that the final result should be the other way around. So it is best to classify CaCl2
as neither acidic or basic if you possibly can.
In reality, I think the basic pH of 8-9 that can be observed when CaCl2
is added to solution probably arises in a complex way. For example, after dissolving calcium chloride in water it can form calcium hydroxide as shown by blue ray above. Calcium hydroxide can further react with CO2
in the air to form calcium carbonate which in water will dissolve to some extent to form bicarbonate ion (HCO3-
). The presence of this ion would also contribute to a slightly raised pH. The extent of all of the above depends on the concentrations of the species involved as well. For instance, the wiki also lists that CaCl2
can be present at a slightly acidic pH (see the wiki for the hydrated compound which can be between 6.5-8) depending on the circumstances. Saying CaCl2
is neither acidic or basic is still the best answer.