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pH Concept

pH Concept. Chapter 16. Self-Ionization of Water. Write a reaction showing water interacting with water. H 2 O(l ) + H 2 O(l)  H 3 O + ( aq ) + OH - ( aq ) If the reaction reaches equilibrium, then a constant ratio of products to reactants exists.

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pH Concept

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  1. pH Concept Chapter 16

  2. Self-Ionization of Water • Write a reaction showing water interacting with water. H2O(l) + H2O(l)  H3O+(aq) + OH-(aq) • If the reaction reaches equilibrium, then a constant ratio of products to reactants exists. • The constant ratio can be calculated in the lab by measuring the concentration of each substance in the reaction and setting up an expression. The expression are called “k” expressions. • Since only solutions (NOT pure liquids, solids, or gases) have concentrations, the expression should only consider aqueous solutions. • The expression for this equation is: k = [H3O+] [OH-] • After many lab tests to confirm, the Kwvalue = 1.0x10-14. This means that water reacting with water will always produce a ratio of ions equal to 1.0x10-14.

  3. Applications of Kw • Water is the solvent in all acid and base dissociation reactions. • In a beaker full of pure water: H2O(l) + H2O(l)  H3O+(aq) + OH-(aq) Kw = [H3O+] [OH-] = 1.0x10-14 • Look closely at the K expression. • Make a prediction. Which ion will increase if an ACID is dissolved in the water? How will the concentration of the other ion respond? • Make a prediction. Which ion will increase if a BASE is dissolved? How will the concentration of the other ion respond?

  4. iRespond Question Multiple Choice F Analysis Level Question #1 Which ion will increase if an BASE is dissolved in the water? How will the concentration of the other ion respond? A.) H3O+ will increase. OH- will increase. B.) H3O+ will increase. OH- will decrease. C.) H3O+ will decrease. OH- will increase. D.) H3O+ will decrease. OH- will decrease. E.)

  5. iRespond Question Multiple Choice F Analysis Level Question #2 Which ion will increase if an ACID is dissolved in the water? How will the concentration of the other ion respond? A.) H3O+ will increase. OH- will increase. B.) H3O+ will increase. OH- will decrease. C.) H3O+ will decrease. OH- will increase. D.) H3O+ will decrease. OH- will decrease. E.)

  6. Hydronium & Hydroxide Rule ACIDS = [H3O+] > [OH-] When a substance dissolves in water and causes the H3O+ concentration to increase, then the OH- concentration will decrease. This signals that the substance is an ACID. When a substance dissolves in water and causes the OH-concentration to increase, then the H3O+ concentration will decrease. This signals that the substance is a BASE. BASES = [OH-] > [H3O+]

  7. Using Kw to Calculate Ion Concentrations • NOTE : H+ = H3O+ • Let’s look at the 19-1 Practice Problems in your practice packet. We’ll solve numbers 1 and 2 together. • What is the concentration of OH- ions in saturated limewater if [H3O+] = 3.98x10-13M? Is the limewater acidic, basic, or neutral? • What is the concentration of H3O+ ions in a wheat flour and water solution is [OH-] = 1.0x10-8M? Is wheat flour and water acidic, basic, or neutral?

  8. 19-1 Practice Problems #1 • What is the concentration of OH- ions in saturated limewater if [H3O+] = 3.98x10-13M? Is the limewater acidic, basic, or neutral? • If the problem involves OH- and H3O+ ions, then you’ll use the kw equation to solve. • [H3O+][OH-]=1.ox10-14 • [3.98x10-13][OH-]=1.0x10-14 • [OH-]=0.0251 M • The OH- value is larger so limewater is a base. • H3O+ = 3.98x10-13vs OH-=0.0251

  9. 19-1 Practice Problems #2 • What is the concentration of H3O+ ions in a wheat flour and water solution is [OH-] = 1.0x10-8M? Is wheat flour and water acidic, basic, or neutral? • If the problem involves OH- and H3O+ ions, then you’ll use the kw equation to solve. • [H3O+][OH-]=1.ox10-14 • [H3O+][1.0x10-8]=1.ox10-14 • [H3O+]=1.0x10-6 M • The H3O+ value is larger so wheat flour is acidic.

  10. iRespond Question Multiple Choice F Application Level Question #3 What is the concentration OH- ions in a potato and water solution if [H3O+] = 1.6x10-6M? Are potatoes and water acidic, basic, or neutral? A.) [OH-] = 1.6x10-20; basic B.) [OH-] = 1.6x10-20; acidic C.) [OH-] = 6.3x10-9; basic D.) [OH-] = 6.3x10-9; acidic E.)

  11. iRespond Question Multiple Choice F Application Level Question #3 What is the concentration OH- ions in a potato and water solution if [H3O+] = 1.6x10-6M? Are potatoes and water acidic, basic, or neutral? A.) [OH-] = 1.6x10-20; basic B.) [OH-] = 1.6x10-20; acidic SET UP: [1.6x10-6][OH-] = 1.0x10-14 C.) [OH-] = 6.3x10-9; basic D.) [OH-] = 6.3x10-9; acidic E.)

  12. iRespond Question Multiple Choice F Application Level Question #4 What is the concentration of H3O+ ions in 0.1M ammonia if [OH-] = 1.26x10-3M? Is ammonia acidic, basic, or neutral? A.) [H3O+] = 7.94x10-12; acidic B.) [H3O+] = 7.94x10-12; basic C.) [H3O+] = 1.26x10-17; acidic E.) D.) [H3O+] = 1.26x10-17; basic

  13. iRespond Question Multiple Choice F Application Level Question #4 What is the concentration of H3O+ ions in 0.1M ammonia if [OH-] = 1.26x10-3M? Is ammonia acidic, basic, or neutral? A.) [H3O+] = 7.94x10-12; acidic B.) [H3O+] = 7.94x10-12; basic SET UP: [H3O+][1.26x10-3] = 1.0x10-14 C.) [H3O+] = 1.26x10-17; acidic E.) D.) [H3O+] = 1.26x10-17; basic

  14. Individual AssignmentPracticing Kw Calculations • Complete 5-10 of the 19-1 Practice Problems before class tomorrow.

  15. pH Concept • Acidic and basic are two extremes that describe a chemical property chemicals. Mixing acids and bases can cancel out or neutralize their extreme effects. A substance that is neither acidic nor basic is neutral. • The pH scale measures how acidic or basic a substance is. The pH scale ranges from 0 to 14. A pH of 7 is neutral. A pH less than 7 is acidic. A pH greater than 7 is basic.

  16. pH Scale • The pH scale is logarithmic. • As a result, each whole pH value below 7 is ten times more acidic than the next higher value. • For example, pH 4 is ten times more acidic than pH 5 and 100 times (10 times 10) more acidic than pH 6. • The same holds true for pH values above 7, each of which is ten times more alkaline (another way to say basic) than the next lower whole value. • For example, pH 10 is ten times more alkaline than pH 9 and 100 times (10 times 10) more alkaline than pH 8.

  17. Calculating pH • pH = -log[H+] OR pH = -log[H3O+] • pH is defined as the negative logarithm of the hydrogen ion (a synonym for hydronium ion) concentration. • We learned to calculate these concentrations using Kw. Therefore, a pH problem might give me the [H+] concentration directly OR indirectly via [OH-].

  18. Calculating pH Examples • Let’s look at the 19-1 Practice Problems in your practice packet again. • Analysis of a sample of maple syrup reveals the concentration of OH- ions is 5.0x10-8 M. What is the pH of this syrup? Is it acidic, basic, or neutral? • In a sample of bananas and water, it is found that [H3O+] = 2.51x10-5 M. What is the corresponding pH value, and are the bananas and water acidic, basic, or neutral?

  19. 19-1 Practice Problems #11 • Analysis of a sample of maple syrup reveals the concentration of OH- ions is 5.0x10-8 M. What is the pH of this syrup? Is it acidic, basic, or neutral? • Shoot! You need [H+] to calculation pH, but the problem is giving me [OH-] instead. • Use the kw equation to get [H+] from [OH-]. • [H+][5.0x10-8]=1.0x10-14 • [H+]=2.0x10-7 • Then, use the pH equation. • pH= -log[H+] • pH=-log[2.0x10-7] • pH = 6.7; Maple syrup is slightly acidic since 6.7 is less than 7.

  20. 19-1 Practice Problems #12 • In a sample of bananas and water, it is found that [H3O+] = 2.51x10-5 M. What is the corresponding pH value, and are the bananas and water acidic, basic, or neutral? • pH= -log[H+] • pH=-log[2.51x10-5] • pH = 4.6; Bananas are acidic since 4.6 is less than 7.

  21. Additional Example of pH • A solution of HCl is prepared by dissolving 1.2 g of HCl in water to make 350 mL of solution. Determine the pH of this solution. • You’ll need the concentration of the [H+] to calculate the pH. Get this by calculating the MOLARITY of the HCl solution. • Molarity = 0.094M • pH=-log[0.094] • pH=1.03

  22. Individual PracticeCalculating pH Values • Complete #13-#20 of the 19-1 Practice Problems before class tomorrow.

  23. pH’s sister - pOH • pOH = -log[OH-] • pH + pOH = 14 • Example 16.6 (pg. 575) • Calculate the pH and pOH for each of the following solutions. • 1.0x10-3M OH- • 1.0 M H+ NOTE: There are multiple ways to calculate these answers.

  24. Individual PracticeCalculating pOH and pH • Examples from page 590-591 in textbook. • Calculate the pH corresponding to each of the pOH values listed. a. pOH = 4.32 b. pOH = 8.90 c. pOH = 1.81 d. pOH = 13.1 Solve the four problems here, and we’ll use the remotes to check your work.

  25. iRespond Question Fill-In F Application Level Question # 5 pg 590 #32 a a. Calculate the pH if pOH= 4.32. A.) 9.68;9.7; B.) C.) D.) E.)

  26. iRespond Question Fill-In F Application Level Question #6 pg 590 #32 b b. Calculate the pH if pOH = 8.90. A.) 5.1;5.10; B.) C.) D.) E.)

  27. iRespond Question Fill-In F Application Level Question #7 pg 590 #32c c. Calculate the pH if the pOH = 1.81. A.) 12.19;12.2; B.) C.) D.) E.)

  28. iRespond Question Fill-In F Application Level Question #8 pg 590 #32 d d. Calculate the pH if the pOH = 13.1. A.) 0.9;.9; B.) C.) D.) E.)

  29. Individual PracticeMore Calculating pOH, pH, & ions • Solve the following. (pg 590 #33) • For each [H+] or [OH-] listed, calculate the concentration of the other ion, the pH, and the pOH of the solution. • [H+] = 1.00x10-7 M • [OH-] = 4.39x10-5 M • [H+] = 4.29x10-11 M • [OH-] = 7.36x10-2 M We’ll check answers with the remote in a moment.

  30. Application Level Question #9 pg.590 #33 a iRespond Question Fill-In F What is the pH when the [H+] = 1.00x10-7 M? (pg.590 #33 a) A.) 7;7.0;7.00 B.) C.) D.) E.)

  31. iRespond Question Fill-In F Application Level Question #10 pg. 590 #33 b What is the pH is the [OH-] = 4.39x10-5M? (pg. 590 #33 b) A.) 9.64;9.6; B.) C.) D.) E.)

  32. iRespond Question Fill-In F Application Level Question #11 pg. 590 #33 c What is the pOH when the [H+] = 4.29x10-11M? (pg. 590 #33 c) A.) 3.63;3.6; B.) C.) D.) E.)

  33. iRespond Question Fill-In F Application Level Question #12 Pg. 590 #33 d What is the pOH if the [OH-] = 7.26x10-2M? (pg. 590 #33 d) A.) 1.13;1.1; B.) C.) D.) E.)

  34. Suggested Individual Practice • Page 589-591 • 7-12 (skip 11c) • 22 a and c • 23 a and c • 24 b • 25 b • 30-31 • 34-35

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