On the pH scale, which numbers indicate a basic solution? An acidic solution? Why?

On the ##pH## scale in aqueous solution, values of ##pH>7## indicate a basic solution………

And of course values of ##pH<7## indicate an acidic solution. ##pH##, literally ##”pouvoir hydrogen”##, measures the concentration of ##H_3O^+##, conceived to be the acidic entity in aqueous solution. Extensive measurement has confirmed the following equilibrium in water under standard conditions:

##2H_2O(aq) rightleftharpoons H_3O^+ + HO^-##

And this reaction can be quantified by taking the ion product:

##[H_3O^+][HO^-]=10^(-14)##

If we take ##-log_10## of both sides we get,

##-log_10[H_3O^+]-log_10[HO^-]=14##

But under our standard defintion of ##pH## and ##pOH##,

##pH+pOH=14##

And thus values of ##pH>7## indicate a preponderance of hydroxide ions, and ##pH<7## indicates a preponderance of hydronium ions.

What is ##pH## at neutrality? Why?


Posted in Uncategorized