# Calculating pH

Course:
Chemistry

pH is a way to measure the relative strengths of acids and bases. We start this video with a quick review of the definition of acid and base, consider whether water is an acid or a base, and then work 3 examples of using the equation for pH. Make sure to watch to the end so you can see the surprising pH of some of our everyday liquids!

What is pH? Historically, as written in older chemistry papers, pH stands for "potential of Hydrogen" (some sources say it might have been "potenz" or "power of Hydrogen" or "pondus or quantity of hydrogen")—but what does that actually mean? What do we use this for?

pH is a way to measure the relative strengths of acids and bases. In general, acids increase the concentration of H+ ions in a solution, while bases decrease the concentration of H+ ions in a solution. If you’re concerned about safety, what you really want to know is the pH.  The pH scale runs from 0 to 14.  Acids have a pH less than 7. Bases have a pH greater than 7. The farther you are from 7, the stronger the acid or base is.

The equation to calculate pH from the concentration of hydrogen ions is

pH = -log[H+]

It's a base 10 logarithmic scale, where something with pH 5 is 10 times more acidic than something with pH 6. pH7 is neutral, and anything with a pH greater than 7 is considered basic (or alkaline), and anything with a pH less than 7 is considered acidic.

We start this video with a quick review of the definition of acid and base, consider whether water is an acid or a base, and then work 3 examples of using the equation for pH.
The second video about pH is a look at the pH of common household liquids. You may be surprised!

Video 1: Calculating pH

Video 2: Household pH

Handout: Calculating pH Video Notes Worksheet

Handout: Household pH Video Notes Worksheet

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Our Chemistry Lessons playlist gives you practical help for the topics that chemistry students often struggle with. Each video has multiple example problems worked out in full. Topics covered include: Balancing Chemical Equations, the MOLE, Gas Laws, Molar Mass, and more.