Some pH, pOH, [H+], [OH-], and Kw Relationships

Chemistry Tutorial

Some pH, pOH, [H+], [OH-], and Kw Relationships

Intro

When dealing with acid/base chemistry some of the quantities can seem difficult to comprehend and even redundant. Try your hand at some of these relations!

Sample Problem

Express these quantities using the others:
Keeping in mind that [H+] * [OH-] = Kw = 10^-14

Solution

Some definitions first:
pH = -log[H+] and pOH = -log[OH-]

Math concepts:
if y = log(x), then x = antilog(y), where antilog(y) is merely 10^y
log(x) + log(y) = log(xy)

Using these definitions and some algebraic manipulation (multiplying both sides by -1), we get: -pH = log[H+] and -pOH = log[OH-], this might seem trivial but by undoing the log we can directly solve for [H+] and [OH-] by taking the antilog, giving us:
[H+] = antilog(-pH) = 10^-pH and [OH-] = antilog(-pOH) = 10^-pOH

Next we can further exploit logarithms even more:
We know [H+] * [OH-] = 10^-14 and by taking -log of both sides we get:
-log([H+] * [OH-]) = -log(10^-14) and by using the mathematical concept above we get:
-log[H+] + -log[OH-] = -log(10^-14) and by using definitions above and solving the right hand side log we get: pH + pOH = 14

So we now have knowledge that:
pH = -log[H+] and pOH = -log[OH-]
[H+] = antilog(-pH) = 10^-pH and [OH-] = antilog(-pOH) = 10^-pOH
[H+] * [OH-] = 10^-14 –> [H+] = (10^-14)/[OH-] and [OH-] = (10^-14)/[H+]
pH + pOH = 14 –> pH = 14 – pOH and pOH = 14 – pH

I hope this was clear enough, and that some of you get some milage out of seeing all these quantities in one place.



About The Author

Efficient Math And Science Tutoring
My love for teaching and mentoring comes from seeing how ineffective teachers can make students not want to be engaged. Once I entered college, I began to see how effective teachers could make the difference for the students. This example made me want to teach later in life. I have experience workin...
Send Email
10 Subjects
KnowRo Tutor
3 Tutorials
$25
Lawrence, KS
Learn

Suggested Tutors for Chemistry Help

Ad

Varsity Tutors

(855) 475-5132 - Award-Winning Academic & Test Prep Tutors

Ad

Air Tutors

One-on-One Ivy Tutoring Partners 24/7

Ad

Link Educational Institute

Link Educational Institute

Siddarth C

Vienna, VA

All Subjects

Leave a Comment

Your email address will not be published. Required fields are marked *

^