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10.4 the p_h_scale

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  • 1. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 1 Chapter 10 Acids and Bases 10.4 The pH Scale
  • 2. 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
  • 3. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 3 pH of Everyday Substances
  • 4. 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 [H3O+ ] = 1 x 10−8 M ___ 3) Sprite soft drink, pH = 3.0 ___ 4) pH = 7.0 ___ 5) [OH− ] = 3 x 10−10 M ___ 6) [H3O+ ] = 5 x 10−12 M Learning Check
  • 5. 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 [H3O+ ] = 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) [H3O+ ] = 5 x 10−12 Solution
  • 6. 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
  • 7. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 7  Mathematically, pH is the negative log of the hydronium ion concentration pH = −log [H3O+ ]  For a solution with [H3O+ ] = 1 x 10−4 , pH = −log [1 x 10−4 ] pH = −[−4.0] pH = 4.0 Calculating pH
  • 8. 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 [H3O+ ]. coefficient decimal places [H3O+ ] = 1 x 10−4 pH = 4.0 [H3O+ ] = 8.0 x 10−6 pH = 5.10 [H3O+ ] = 2.4 x 10−8 pH = 7.62
  • 9. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 9 Guide to Calculating pH
  • 10. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 10 Find the pH of a solution with a [H3O+ ] of 1.0 x 10−3 . STEP 1 Enter the [H3O+ ] 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): [H3O+ ] = 1.0 x 10−3 pH is 3.00 Example of Calculating pH
  • 11. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 11 Learning Check What is the pH of coffee if the [H3O+ ] is 1 x 10−5 M? 1) pH = 9.0 2) pH = 7.0 3) pH = 5.0
  • 12. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 12 Solution What is the pH of coffee if the [H3O+ ] is 1 x 10−5 M? STEP 1 Enter the [H3O+ ] 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): [H3O+ ]= 1 x 10−5 , pH is 5.0 (3)
  • 13. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 13 The [H3O+ ] 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
  • 14. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 14 The [H3O+ ] of tomato juice is 2 x 10−4 M. What is the pH of the solution? STEP 1 Enter the [H3O+ ] 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): [H3O+ ] = 2 x 10−4 , pH is = 3.7 (2) Solution
  • 15. 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) 3.00 2) 11.00 3) –11.00 Learning Check
  • 16. 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 [H3O+ ] value: Use the Kw to obtain [H3O+ ] = 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): [H3O+ ] =1.0 x 10−11 , pH is = 11.00 (2) Solution
  • 17. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 17 [H3O+ ], [OH- ], and pH Values
  • 18. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 18 Example 1: Calculating [H3O+ ] from pH Calculate the [H3O+ ] for a pH value of 8.0. [H3O+ ] = 1 x 10−pH For pH = 8.0, the [H3O+ ] = 1 x 10−8 STEP 1 Enter the pH value, change sign: –8.0 STEP 2 Convert −pH to concentration: Use 2nd function key and then10x 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): [H3O+ ] = 1 x 10−8 M
  • 19. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 19 Example 2: Calculating [H3O+ ] from pH Calculate the [H3O+ ] for a pH of 3.80. STEP 1 Enter the pH value, change sign: –3.80 STEP 2 Convert −pH to concentration: Use 2nd function key and then10x key or inverse key and then log key 1.584893 −06 STEP 3 Adjust the significant figures in the coefficient (2 digit following decimal point = 2 digit in the coefficient): [H3O+ ] = 1.6 x 10−6 M
  • 20. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 20 What is the [H3O+ ] of a solution with a pH of 10.0? 1) 1 x 10−4 M 2) 1 x 1010 M 3) 1 x 10−10 M Learning Check
  • 21. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 21 What is the [H3O+ ] of a solution with a pH of 10.0? STEP 1 Enter the pH value, change sign: –10.0 STEP 2 Convert −pH to concentration: Use 2nd function key and then10x 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): [H3O+ ] = 1 x 10−10 M (3) Solution
  • 22. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 22 What is the [H3O+ ] 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
  • 23. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 23 What is the [H3O+ ] of a solution with a pH of 2.85? STEP 1 Enter the pH value, change sign: –2.85 STEP 2 Convert −pH to concentration: Use 2nd function key and then10x key or inverse key and then log key 0.0014125 = 1.4125 x 10−03 STEP 3 Adjust the significant figures in the coefficient (2 digits following decimal point = 2 digits in the coefficient): [H3O+ ] = 1.4 x 10−3 M (2) Solution