Everything You Need in One Place

Homework problems? Exam preparation? Trying to grasp a concept or just brushing up the basics? Our extensive help & practice library have got you covered.

Learn and Practice With Ease

Our proven video lessons ease you through problems quickly, and you get tonnes of friendly practice on questions that trip students up on tests and finals.

Instant and Unlimited Help

Our personalized learning platform enables you to instantly find the exact walkthrough to your specific type of question. Activate unlimited help now!

0/3
?
Intros
Lessons
  1. Relating pH, H3O+ and Kw.
  2. Defining pH and pOH.
  3. Antilogs: Using pH and pOH to find [H3O+] and [OH-].
  4. Connecting pH → [H3O+] → [OH-] → pOH → pH
0/2
?
Examples
Lessons
  1. Find the concentration of acidic and basic solutions when given from the pH.
    1. A solution of HCl, a strong acid, has a pH of 1.74. What is the H3O+(aq) concentration of this solution? Give your answer to three significant figures.
    2. A solution of potassium hydroxide, KOH, has a pH of 12.89. Find the concentration of OH-(aq) ions in this solution. Give your answer to three significant figures.
Free to Join!
StudyPug is a learning help platform covering math and science from grade 4 all the way to second year university. Our video tutorials, unlimited practice problems, and step-by-step explanations provide you or your child with all the help you need to master concepts. On top of that, it's fun - with achievements, customizable avatars, and awards to keep you motivated.
  • Easily See Your Progress

    We track the progress you've made on a topic so you know what you've done. From the course view you can easily see what topics have what and the progress you've made on them. Fill the rings to completely master that section or mouse over the icon to see more details.
  • Make Use of Our Learning Aids

    Last Viewed
    Practice Accuracy
    Suggested Tasks

    Get quick access to the topic you're currently learning.

    See how well your practice sessions are going over time.

    Stay on track with our daily recommendations.

  • Earn Achievements as You Learn

    Make the most of your time as you use StudyPug to help you achieve your goals. Earn fun little badges the more you watch, practice, and use our service.
  • Create and Customize Your Avatar

    Play with our fun little avatar builder to create and customize your own avatar on StudyPug. Choose your face, eye colour, hair colour and style, and background. Unlock more options the more you use StudyPug.
Topic Notes
?

In this lesson, we will learn:

  • To recall the expressions for pH and pOH.
  • To use the antilog to relate pH and pOH back to aqueous ion concentration.
  • How pH and pOH are related to the Kw expression.

Notes:

  • We learned earlier in Introduction to acid-base theory , that pH is defined by the concentration of H3O+ ions in solution:

    pH = -log[H3O+]

  • In the same way, pOH can be measured, which is defined by the concentration of OH- ions in solution:

    pOH = -log[OH-]

    Be careful with significant figures – with logarithms, only the values in decimal places are considered significant figures.

  • The reverse of the logarithm is known as the antilog, so the antilog can be used to convert pH into [H3O+] and pOH into [OH-]. The antilog is found by rising 10 to the value for which you are getting the antilog:

    Antilog (x) = 10 x


    Make sure your calculator gives antilogs in scientific notation, or standard form. As stated above, the decimal places are the significant figures in a logarithm value. The first digit represents the order of magnitude. For example, log(10) = 2.0 and log(100) = 3.0; 3 is one greater than 2, so 3 as a logarithm is one order of magnitude (10x) greater than 2 as a logarithm.

    With this, we can show expressions to find [H3O+] and [OH-] using pH and pOH:

    [H3O+] = 10 -pH
    [OH-] = 10 -pOH

  • Because [H3O+] and [OH-] in aqueous solution at 25oC are related to Kw, pH and pOH are related to pKw – which is just the negative log of the Kw constant!
    • pH and pOH give logarithmic expressions of the aqueous ion concentration. Recall that:

      Kw = [H3O+(aq)] [OH-(aq)] = 1.00 βˆ—* 10 -14 at 25oC

      Taking the negative log of these aqueous ion concentrations, we can determine:

      pH + pOH = pKw = 14

      With these we can relate the four expressions in a β€˜grid’ below: