Unit 4, Lesson 19

Suppose you have a solution whose pH you know, but whose concentration of H+ ions and OH- ions you don't know. There's a simple formula you can use to find any of your missing links, and it is as follows:

pH = -log[ H+]

[ H+] = 10^-pH

The first equation is used to find the pH of the substance if the number of hydrogen ions (which is listed in scientific notation) is known. The second, scientists use to find hydrogen ions by taking the pH, making it a negative number, and writing it in scientific notation.

To find OH- ions, know that the product of hydrogen and hydroxide ions is always equivalent to 1 x 10^-14. If you know one value of ions, divide 1 x 10^-14 by it to find the other value.

Problems:

7.) What is the pH of a 2.5 M HCl solution? The pH of this solution is 0, because the decimal is after the 2, not before. Its H+ concentration is 1 x 10^0.

8.) What is the pH of a 0.256 M NaOH solution? 11. The H+ concentration is 1 x 10^-11, the OH- concentration is 1 x 10^-3.