Question

The ph scale is a way of comparing...?

Answer 1

Acidity..........specifically `[H_3O^+]`

Explanation:

AS you know in water the following equilibrium operates...

`2H_2O(l)rightleftharpoonsH_3O^+ + HO^-`

Which is certainly measurable....and under standard conditions...

`K_w=10^-14=[HO^+][H_3O^+]`

ANd we may take `log_10` of both sides to get,,,,

`underbrace(-log_10[H_3O^+])_(pH)+underbrace(-log_10[HO^-])_(pOH)` `=` `-log_10K_w`

Now `K_w=10^-14`, and thus we get our working relationship....

`pH+pOH=14`

And so when `[H_3O^+]` is high, `pH` is low, and when `[HO^-]` is high, `pH` is high, and `pOH` low....