I think, and I am not sure, but HClO3 is produced which is a strong acid. This would lower the pH of the solution.
I don't know how advanced you class is but I would offer two or three suggestions.
1. The temperature of the water was not 25 C where Kw for H2O is 1.008E-14.
2. The ionic strength of the solution was not taken into account.
3. The water used for the experiment had CO2 (from air) dissolved in it. It doesn't take much to drop the pH from 7.0 to 6.0.
4. You didn't calibrate the pH meter before use (or it wasn't calibrated properly).
I would discount the HClO3 theory. KClO3 is the salt of a strong acid (HClO3) and a strong base (KOH). Neither K ion nor ClO3- are hydrolyzed so the pH should be 7.0. The USUAL reason why so-called pure water is not 7.0 is because of dissolved CO2. Did you know that the pH of 0.1M NaCl is not 7.0. You can work out the activity of the H^+ and OH^- in 0.1M NaCl with the Debye-Huckel theory and the pH turns out not to be 7.0 (because of the ionic strength of the solution).
I made a grammatical error in my post above. I should have written "Neither K ion nor ClO3^- IS hydrolyzed......" Ten whacks with a wet noodle for me.
I know that KClO3 is a salt or a strong acid and strong base, but if the salt was isolated, and added to water
The reaction should be
2(KClO3) + H2O --> K2O + 2(HClO3)
Thus decreasing the pH.
I initially thought KClO3 + H2O----> KOH +HClO3, but I am getting the reaction above, which is why I suggested the HClO3 theory, but again I am not sure.
I don't think so.
1. There is nothing to drive the reaction that way. I found delta H formation for K2O, KClO3, and H2O but couldn't find dHf for HClO3. If you can find dHf for HClO3 you can calculate the dHf reaction you've proposed and see there is nothing to drive it.
2. K2O is a base and HClO3 an acid; they can't exist separately in solution. You get K^+ and ClO3^- ions and that's it.
I was looking for info. to prove the HClO3 theory or otherwise, and I can not find any information. To be honest, your third theory sounds like it would be the most plausible.