General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.1 The pH Scale

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.2 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  is acidic when the values are less than 7  is neutral with a pH of 7  is basic when the values are greater than 7

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.3 pH of Everyday Substances

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.4 Identify each solution as A) acidic, B) basic, or N) neutral ___ 1) HCl with a pH = 1.5 ___ 2) pancreatic fluid [H 3 O + ] = 1 x 10 −8 M ___ 3) Sprite soft drink, pH = 3.0 ___ 4) pH = 7.0 ___ 5) [OH − ] = 3 x 10 −10 M ___ 6) [H 3 O + ] = 5 x 10 −12 M Learning Check

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.5 Identify each solution as A) acidic, B) basic, or N) neutral A 1) HCl with a pH = 1.5 B 2) Pancreatic fluid [H 3 O + ] = 1 x 10 −8 M A 3) Sprite soft drink pH = 3.0 N 4) pH = 7.0 A 5) [OH - ] = 3 x 10 −10 M B 6) [H 3 O + ] = 5 x 10 −12 Solution

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.6 Testing the pH of Solutions The pH of solutions can be determined using  a pH meter  pH paper  indicators that have specific colors at different pH values

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.7  Mathematically, pH is the negative log of the hydronium ion concentration pH = −log [H 3 O + ]  For a solution with [H 3 O + ] = 1 x 10 −4, pH = −log [1 x 10 −4 ] pH =  [  4.0] pH = 4.0 Calculating pH

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.8 Significant Figures in pH When expressing log values, the number of decimal places in the pH is equal to the number of significant figures in the coefficient of [H 3 O + ]. coefficient decimal places [H 3 O + ] = 1 x 10 −4 pH = 4.0 [H 3 O + ] = 8.0 x 10 −6 pH = 5.10 [H 3 O + ] = 2.4 x 10 −8 pH = 7.62

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.9 Guide to Calculating pH

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.10 Find the pH of a solution with a [H 3 O + ] of 1.0 x 10 −3. STEP 1 Enter the [H 3 O + ] value: Enter 1 x 10  3 (press 1 EE 3, then change sign) The EE key gives the exponent of 10. STEP 2 Press log key and change the sign:  log (1 x 10 −3 ) =  [  3] STEP 3 Make the number of digits after the decimal point (2) equal to the number of significant figures in the coefficient (2): [H 3 O + ] = 1.0 x 10 −3 pH is 3.00 Example of Calculating pH

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.11 Learning Check What is the pH of coffee if the [H 3 O + ] is 1 x 10 −5 M? 1) pH = 9.0 2) pH = 7.0 3) pH = 5.0

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.12 Solution What is the pH of coffee if the [H 3 O + ] is 1 x 10 −5 M? STEP 1 Enter the [H 3 O + ] value: Enter 1 x 10  5 (press 1 EE 5, then change sign ) STEP 2 Press log key and change the sign:  log (1 x 10 −5 ) =  [  5] STEP 3 Make the number of digits after the decimal point (1) equal to the number of significant figures in the coefficient (1): [H 3 O + ]= 1 x 10 −5, pH is 5.0 (3)

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.13 The [H 3 O + ] of tomato juice is 2 x 10 −4 M. What is the pH of the solution? 1) 4.0 2) 3.7 3) 10.3 Learning Check

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.14 The [H 3 O + ] of tomato juice is 2 x 10 −4 M. What is the pH of the solution? STEP 1 Enter the [H 3 O + ] value: Enter 2 x 10  4 (press 2 EE 4, then change sign ) STEP 2 Press log key and change the sign:  log (2 x 10 −4 ) =  [  3.7] STEP 3 Make the number of digits after the decimal point (1) equal to the number of significant figures in the coefficient (1): [H 3 O + ] = 2 x 10 −4, pH is = 3.7 (2) Solution

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.15 The [OH − ] of a solution is 1.0 x 10 −3 M. What is the pH? 1) ) ) –11.00 Learning Check

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.16 The [OH − ] of a solution is 1.0 x 10 −3 M. What is the pH? STEP 1 Enter the [H 3 O + ] value: Use the K w to obtain [H 3 O + ] = 1.0 x 10 − 11 M Enter 1.0 x 10 − 11 (press 1 EE 11, then change sign) STEP 2 Press log key and change the sign:  log (1.0 x 10 − 11 ) =  [  11] STEP 3 Make the number of digits after the decimal point (2) equal to the number of significant figures in the coefficient (2): [H 3 O + ] =1.0 x 10 −11, pH is = (2) Solution

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.17 [H 3 O + ], [OH - ], and pH Values

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.18 Example 1: Calculating [H 3 O + ] from pH Calculate the [H 3 O + ] for a pH value of 8.0. [H 3 O + ] = 1 x 10 − pH For pH = 8.0, the [H 3 O + ] = 1 x 10 − 8 STEP1 Enter the pH value, change sign: –8.0 STEP2 Convert  pH to concentration: Use 2 nd function key and then10 x key or inverse key and then log key 1 − 08 STEP 3 Adjust the significant figures in the coefficient (1 digit following decimal point = 1 digit in the coefficient): [H 3 O + ] = 1 x 10 − 8 M

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.19 Example 2: Calculating [H 3 O + ] from pH Calculate the [H 3 O + ] for a pH of STEP1 Enter the pH value, change sign: –3.80 STEP2 Convert  pH to concentration: Use 2 nd function key and then10 x key or inverse key and then log key − 06 STEP 3 Adjust the significant figures in the coefficient (2 digit following decimal point = 2 digit in the coefficient): [H 3 O + ] = 1.6 x 10 − 6 M

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.20 What is the [H 3 O + ] of a solution with a pH of 10.0? 1) 1 x 10 − 4 M 2) 1 x M 3) 1 x 10 − 10 M Learning Check

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.21 What is the [H 3 O + ] of a solution with a pH of 10.0? STEP1 Enter the pH value, change sign: –10.0 STEP2 Convert  pH to concentration: Use 2 nd function key and then10 x key or inverse key and then log key 1 − 10 STEP 3 Adjust the significant figures in the coefficient (1 digit following decimal point = 1 digit in the coefficient): [H 3 O + ] = 1 x 10 − 10 M (3) Solution

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.22 What is the [H 3 O + ] of a solution with a pH of 2.85? 1) 1.0 x 10 − 2.85 M 2) 1.4 x 10 − 3 M 3) 8.5 x 10 − 2 M Learning Check

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.23 What is the [H 3 O + ] of a solution with a pH of 2.85? STEP1 Enter the pH value, change sign: –2.85 STEP2 Convert  pH to concentration: Use 2 nd function key and then10 x key or inverse key and then log key = x 10 − 03 STEP 3 Adjust the significant figures in the coefficient (2 digits following decimal point = 2 digits in the coefficient): [H 3 O + ] = 1.4 x 10 − 3 M (2) Solution