# Is calcium chloride an acidic or basic salt?

What I reason: Calcium chloride is the salt of hydrochloric acid and calcium hydroxide. Calcium hydroxide is usually not considered a strong base, and I believe this is because of it's low solubility. $$\ce{HCl}$$ is a strong acid, and so the salt should be slightly acidic. Wikipedia states the $$\mathrm{p}K_\mathrm{a}$$ of $$\ce{CaCl2}$$ is between 8-9, which is in fact slightly acidic, confirming my theory.

What I've experienced: I've prepared a number of aqueous calcium chloride solutions from distilled water, all of which are purple in the presence of universal indicator and tested with a calibrated $$\mathrm{pH}$$ probe to be basic. I've tried multiple sources of calcium chloride and each is basic.

TLDR: Theoretically and literature values state that $$\ce{CaCl2}$$ is acidic, but my empirical evidence shows that it is basic.

$$\ce{CaCl2}$$ solutions should be very slightly acidic if they were made from pure $$\ce{CaCl2}$$. This might not be the case. In industry calcium chloride is produces by reaction of calcium hydroxide with ammonium chloride, so industrial-grade calcium chloride is likely to be contaminated with calcium hydroxide.
• @AdnanAL-Amleh pH+pOH is roughly 14. For Ca(OH)2 solution [OH] is roughly twice molar concentration of calcium hydroxide, which is roughly 0.025 for saturated solution. $pOH = -log [OH]$; $log_{10} 0.025 = 1.6$; $14-1.6 > 12$. You don't need much base to create a strongly basic solution. – permeakra May 10 '19 at 20:48
• You mean : $\ce{Ca(OH)2_\mathrm{(aq)} <=>Ca(OH)^+_\mathrm{(aq)} + OH^-_\mathrm{(aq)}}$ , so: $$[\ce{OH-}]=[\ce{Ca(OH)2}] = \frac{1.9}{74}=\pu{0.025M}$$ – Adnan AL-Amleh May 10 '19 at 22:27
• @AdnanAL-Amleh Yes. 0.025 M for $[OH-]$ is a low estimate, it is probably higher because $\ce{Ca(OH)+}$ can dissociate too. – permeakra May 10 '19 at 22:55