How do you determine pH from molarity?

1 Answer
Mar 6, 2014

Molarity is also known as the concentration. The concentration can be converted to #"pH"#.

Take a sample of nitric acid #"HNO"_3# with a molarity of #"0.0032 M"#.

The molarity becomes the #["H"^+]# concentration of #3.2 xx 10^(-3)#.

We know this is the #["H"^+]# concentration because #"HNO"_3# is a strong acid, since the acid will completely dissociate into #"H"^+# and #"NO"_3^-#.

To find the #"pH"# calculate #- log["H"^+]#

#-log[3.2xx 10^(-3)] = 2.49 = "pH"#

To find the #"pOH"# take the #"pH"# value and subtract it from #14#.

#14 - 2.49 = 11.51 = "pOH"#

To convert #"pOH"# to #["OH"^-]# calculate #["OH"^-]=10^(-"pOH")#

#10^(-11.51)= 3.09 xx 10^(-12)=["OH"^-]#