Chapter 14 Acids and Bases 14.6 The pH Scale Learning Goal Calculate the pH from [H3O+]; given the pH, calculate the [H3O+] and [OH−] of a solution. © 2014 Pearson Education, Inc.

is used to indicate the acidity of a solution The pH Scale The pH of a solution is used to indicate the acidity of a solution has values that usually range from 0 to 14 © 2014 Pearson Education, Inc.

pH of Common Substances © 2014 Pearson Education, Inc.

Identify each solution as acidic, basic, or neutral. Learning Check Identify each solution as acidic, basic, or neutral. A. HCl with a pH = 1.5 pancreatic fluid [H3O+] = 1 × 10−8 M C. soft drink pH = 3.0 D. pH = 7.0 [OH−] = 3 × 10−10 M [H3O+ ] = 5 × 10−12 © 2014 Pearson Education, Inc.

Identify each solution as acidic, basic, or neutral. A. HCl with a pH = 1.5 acidic pancreatic fluid [H3O+] = 1 × 10−8 M basic C. soft drink pH = 3.0 acidic D. pH = 7.0 neutral [OH−] = 3 × 10−10 M acidic [H3O+ ] = 5 × 10−12 basic © 2014 Pearson Education, Inc.

The pH of solutions is determined by using a pH meter pH paper, or Testing for pH The pH of solutions is determined by using a pH meter pH paper, or indicators that have specific colors at different pH values © 2014 Pearson Education, Inc.

For a solution with [H3O+] = 1.0 × 10−4 M pH = −log [1.0 × 104 ] Calculating pH pH is defined as the negative logarithm (log) of the hydronium ion concentration. pH = −log[H3O+] For a solution with [H3O+] = 1.0 × 10−4 M pH = −log [1.0 × 104 ] pH = −[−4.00] pH = 4.00 © 2014 Pearson Education, Inc.

pH, Significant Figures When expressing pH values, the number of decimal places is equal to the number of significant figures in the coefficient of [H3O+]. coefficient decimal places [H3O+] = 1 × 104 pH = 4.0 [H3O+] = 2.4 × 108 pH = 7.62 © 2014 Pearson Education, Inc.

Guide to Calculating pH © 2014 Pearson Education, Inc.

Learning Check Acetylsalicylic acid, known as aspirin, was the first nonsteroidal anti-inflammatory drug used to alleviate pain and fever. If a solution of aspirin has a [H3O+] = 1.7 × 10−3 M, what is the pH of the solution? © 2014 Pearson Education, Inc.

Step 1 State the given and needed quantities. Solution If a solution of aspirin has a [H3O+] = 1.7 × 10−3 M, what is the pH of the solution? Step 1 State the given and needed quantities. Given Need Know [H3O+] = 1.7 × 10−3 M pH pH = −log[H3O+] © 2014 Pearson Education, Inc.

Solution If a solution of aspirin has a [H3O+] = 1.7 × 10−3 M, what is the pH of the solution? Step 2 Enter the [H3O+] into the pH equation. pH = −log[H3O+] = −log[1.7 × 10−3 ] Procedure: Enter 1.7, press Enter 3, press to change sign. EE or Exp /−+ © 2014 Pearson Education, Inc.

Solution If a solution of aspirin has a [H3O+] = 1.7 × 10−3 M, what is the pH of the solution? Step 3 Press the log key and change the sign. Procedure: Press Calculator display Adjust the number of SFs on the right of the decimal point. pH = 2.77 log +/− 2.769551079 © 2014 Pearson Education, Inc.

Calculate the pH of a solution with [OH−] of 4.0 × 10−5 M. Learning Check Calculate the pH of a solution with [OH−] of 4.0 × 10−5 M. © 2014 Pearson Education, Inc.

Calculate the pH of a solution with [OH−] of 4.0 × 10−5 M. Step 1 State the given and needed quantities. Given Need Know [OH−] = 4.0 × 10−5 M [H3O+] pH Kw = [H3O+] [OH−] pH = −log[H3O+] © 2014 Pearson Education, Inc.

Calculate the pH of a solution with [OH−] of 4.0 × 10−5 M. Step 2 Enter the [H3O+] into the pH equation. pH = −log[2.5 × 10−10] = 2.5 10 EE or Exp +/− = © 2014 Pearson Education, Inc.

Solution Calculate the pH of a solution with [OH−] of 4.0 × 10−5 M. Step 3 Press the log key and change the sign. Press Calculator display 9.60205 Adjust the number of SFs on the right of the decimal point. pH = 9.60 log +/− © 2014 Pearson Education, Inc.

a high [OH−] have low pOH values a low [OH−] have high pOH values The pOH scale is similar to the pH scale, except that pOH is associated with the OH− concentration of an aqueous solution. pH = −log[OH−] Solutions with a high [OH−] have low pOH values a low [OH−] have high pOH values © 2014 Pearson Education, Inc.

In any aqueous solution, pH + pOH = 14.00 and pOH = 14 − pH In a solution with a pH of 3.50, we can calculate the pOH from the pH. pOH = 14 − 3.50 = 10.50 © 2014 Pearson Education, Inc.

pH and pOH © 2014 Pearson Education, Inc.

pH and pOH © 2014 Pearson Education, Inc.

Calculating [H3O+] from pH Given the pH of a solution, [H3O+] can be calculated: [H3O+] = 10−pH If the pH of a solution is 3.0: [H3O+] = 1 × 10−3 M For pH values that are not whole numbers, the 10x key on your calculator can be used. © 2014 Pearson Education, Inc.

Guide to Calculating [H3O+] from pH © 2014 Pearson Education, Inc.

Calculate [H3O+] for a solution of baking soda with a pH of 8.25. Learning Check Calculate [H3O+] for a solution of baking soda with a pH of 8.25. © 2014 Pearson Education, Inc.

Calculate [H3O+] for a solution of baking soda with a pH of 8.25. Step 1 State the given and needed quantities. Given Need Know pH = 8.25 [H3O+] [H3O+] = 10−pH © 2014 Pearson Education, Inc.

Calculate [H3O+] for a solution of baking soda with a pH of 8.25. Step 2 Enter the pH value into the inverse log equation and change the sign. 8.25 = −8.25 Press the 2nd function key and then the 10x key. = 5.623413252−09 +/− 2nd 10x © 2014 Pearson Education, Inc.

Solution Calculate [H3O+] for a solution of baking soda with a pH of 8.25. Step 3 Adjust the SFs in the coefficient. [H3O+] = 5.6 × 10−9 M © 2014 Pearson Education, Inc.