This document provides information on calculating hydrogen ion concentration ([H+]) from pH. It states that pH = -log[H+] and [H+] = 10-pH. It then provides two examples: 1) A Coke has pH of 3.12, so [H+] = 10-3.12 = 7.6 x 10-4 M, indicating it is acidic. 2) A solution has pH of 8.5, so [H+] = 10-8.5 = 3.16 x 10-9 M, indicating it is a weak base.

1. PH
CALCULATIONS
Objective :
Calculate hydrogen ion concentration when given the PH.

2. WHAT IS THE
PH SCALE?
The pH scale measures how acidic or basic a
solution is.

3. [H+] = 10-PH
when the PH is given, and
you want to find [H+]
hydrogen ion concentration
Use this formula
[H+] = 10-pH

4. SOLVING
FOR [H+]
EX 1 :
If the pH of a Coke is 3.12, [H+] = ???
Because pH = - log [H+]
then
[H+] = 10-pH
[H+] = 10-3.12 = 7.6 x 10-4 M
*** to find antilog on your calculator, look for
“Shift” or “2nd function” and then the log
button
pH = 3.12
It is an acid

5. EXAMPLE :2
A solution has a pH of 8.5. What is the Molarity of
hydrogen ions in the solution [H+]
Note (this example is explained in detail , you can
go directly to the fifth step and find the answer )
pH of 8.5 means , it is a weak base
pH = - log [H+]
8.5 = - log [H+]
-8.5 = log [H+]
Antilog -8.5 = antilog (log [H+])
10-8.5 = [H+]
3.16 X 10-9 = [H+]

6. TRY THESE
[H+] = 10-pH
• [H+] =
Question 1 : If pH = 10
• [H+] =
Questioin 2 : If pH = 4.74

7. PH CALCULATIONS
 pH = - log [H+]
 [H+] = 10-pH

8. HOME-WORK
The letters “pH” represent the French words “pouvoir hydrogene” which means
“hydrogen power”.
•The definition of pH is pH is equal to the negative log (logarithm) of the
____________ ion concentration of a solution.
•The logarithm of a number is the power to which 10 must be raised to
equal that number.
A pH value of less than 7 indicates a(n) _______________ solution. A pH value
of _____ indicates a neutral solution. A pH value of more than 7 indicates a(n)
_______________ solution.

9. PROBLEMS: SHOW ALL WORK AND CIRCLE THE FINAL ANSWER.
1. Determine the pH of a 0.010 M HNO3 solution.
Is this solution acidic or basic? _____________
2.What is the pH of a 2.5 x 10-6 M solution of HCl?
Is this solution acidic or basic? _____________

10. What is the hydrogen ion concentration of an aqueous HCl solution that has
a pH of 3.0?
Is this solution acidic or basic? _____________