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Posted: Fri Jan 18, 2019 1:35 am
I don't really understand what the autoprotolysis constant is and what it's function/use is
Posted: Fri Jan 18, 2019 2:47 am
The autoprotolysis constant of water allows us to easily find out the concentration of H3O+ and OH- when we have one or the other. By comparing the concentrations of hydronium and hydroxide ions, we can see if it is an acidic or basic solution. Additionally, Kw connects to Ka, Kb, pKa, pKb, and pH through several formulas that allow us to easily switch between acids/bases, find concentrations, and pH. Hope this helps!
Posted: Fri Jan 18, 2019 3:24 pm
When water goes through autoprotolysis, it produces a small amount of H30+ and OH-.
H20 (l) goes to form OH - (aq) and H30+ (aq). If you write the K expression, it is K = [OH-][H3O+]. When measuring these values in pure water, [OH-] and [H3O+] both equal 1 x 10^-7 and K equals 1 x 10^-14. We call this K Kw because it is the equilibrium constant of water at 25 degrees celsius and always equal 1 x 10^-14 at this temperature. Kw is very useful because typically things are dissolved in water and we can use this fact to solve for the hydroxide and hydronium concentrations in a solution if one is known.