The pH and pOH Scales

The pH and pOH scales provide a convenient way to express the acidity and basicity of dilute aqueous solutions. The pH and pOH of a solution are defined as 

We are given the value for [H30 j so we take the negative logarithm of this value. Solution 

This answer contains only mo significant figures. The 1 in 1.30 is not a significant figure it comes from the power of ten. 

In a pH value, only the digits after the decimal point are significant figures. 

The pH of a solution is 3.301. What is the concentration of H3O+ in this solution Plan 

---

Because the pH and pOH scales are based on logarithms, a change in 1 pH or pOH unit represents a change in ion concentration of a factor of ten. Coffee with a pH of 5 has approximately 100 times the hydronium ion concentration as tap water with a pH of 7. 

The pH and pOH scales are shorthand notations, in a sense. Instead of writing that the concentration of hydronium ions in a particular solution is 0.00001 M (or, 1 X 10 5 M, in scientific notation), we simply say that the pH of the solution is 5. How do we convert between the concentration of the ions and the pH or pOH scales We simply use the following formulas. 

A little trick that you should learn early on (especially if your calculator lacks a log button) is that when the coefficient in your concentration of hydronium ions is 1, as in 1 x 10 8, the pH is equal to the absolute value of the exponent. The pOH scale is used in a similar way to indicate the concentration of hydroxide ions in a solution. A concentration of hydroxide ions of 1 x 103 would correspond to a 3 on the pOH scale. The following table summarizes the method of converting the concentrations of hydronium ions and hydroxide ions to the pH and pOH scales respectively. 

To develop familiarity with the pH and pOH scales, consider a series of solutions in which [H3O+] varies from 10 M to 1.0 X 10-1 M. Obviously, [OH-] will vary from 1.0 X 10-1 M to 10 M in these solutions. Table 18-3 summarizes these scales. 

A Review of Strong Electroiytes 18-2 The Autoionization of Water 18-3 The pH and pOH Scales 18-4 Ionization Constants for Weak Monoprotic Adds and Bases 18-5 Poly protic Adds 18-6 Solvolysis... 

Sour Patch Kids 14.5 Reactions of Acids 14.9 The pH and pOH Scales ... 

---