This may not even be a valid question, as I may have misunderstood; but here goes... At 25C, the KW of water is 1 x 10-14 If you increase the amount of hydogen ions present, why does the concentration of hydroxyl ions present alter in such a way that the KW is maintained (i.e. the product of the concentrations of hydrogen and hydroxyl ions)? If you introduce protons, then they may associate with water to form hydroxonium ions, or they may associate with hydroxyl ions; in the first there will be an incraese in the hydrogen ion concentration, in the second there will be more water formed, which decreases the hydroxyl concentration but does not alter the hydrogen ion concentration. If it was a mixture of the two (that is, if the protons introduced interact with water both water and hroxyl ions), I still can't see how the two concentrations would be balanced so that the KW is maintained. No textbooks seem to give a reason, which suggests I've misunderstood. Can someone help me with this?