Why is 1.0x10^-7 considered neutral?

[506200887]

Today in lecture we went from multiplying (1.0x10^-7) (1.0x10^-7) and getting the value 10^-14. I do not understand why you would assume that although the concentrations have to be equal for OH- and H3O+ why would it be 1.0x10^-7. Also it seems counter intuitive to start with the concentrations to prove that 7 is neutral on the pH scale.

[Holly Hadsall 2H]

1*10^-7 is considered a neutral concentration of either H+ or OH- because the pH/pOH of both solution would be equal to 7.

[Andrew Rizk]

The reason we were able to start off with multiplying (1.0x10^-7) (1.0x10^-7) and getting the value 10^-14 is because we were working with pure water. In pure water, the concentration of hydronium and hydroxide ions must be equal. We also know the pH of pure water is 7. Thus, using the formulas to convert pH to hydronium concentration, we know that its concentration is 1.0x10^-7 and thus the same must be true for the hydroxide concentration. You do not start with the concentrations to prove 7 is neutral, you know 7 is the pH of water and thus work backwords to figure out its H3O and HO concentrations.