What pH level is considered to be acidic and basic?

1 Answer
anor277
Dec 6, 2016

In aqueous solution, for #pH# #<# #7#, an acidic solution is specified...........

Explanation:

And for #pH# #># #7#, a basic solution is described. For #pH=7#, we describe a NEUTRAL solution.

But what is #pH#?

#pH# is a measure of the concentration of hydronium ion, #[H_3O^+]#, i.e. #pH=-log_10[H_3O^+]#. Equivalently, #pH=-log_10[H_^+]#. #H_3O^+# and #H^+# are used to represent the #"acidium ion"# in aqueous solution.

The use of logarithms is a bit old-fashioned, but back in the day A level students used to used log tables, before the advent of cheap electronic calculators.

For water:

#pH# #=# #-log_10[H_3O^+]#

#pOH# #=# #-log_10[HO^-]#

Now #K_w# #=# #[H_3O^+][HO^-]# #=# #10^(-14)" at 298K"#.

Thus #-log_10K_w=-log_10[H_3O^+] -log_10[HO^-]#

#=-log_10(10^-14)# #=# #+14#

And thus #pOH+pH=14# under standard conditions.

You should review the logarithmic function if you have any problem with this treatment. You should review it anyway, because I might have made a mistake.

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