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 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.

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Presentation on theme: " 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."— Presentation transcript:

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2  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.  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 = [H 3 O + ] [OH - ]  After many lab tests to confirm, the K w value = 1.0x This means that water reacting with water will always produce a ratio of ions equal to 1.0x

3  Water is the solvent in all acid and base dissociation reactions.  In a beaker full of pure water: H 2 O(l) + H 2 O(l)  H 3 O + (aq) + OH - (aq) K w = [H 3 O + ] [OH - ] = 1.0x  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 Which ion will increase if an BASE is dissolved in the water? How will the concentration of the other ion respond? A.) H 3 O + will increase. OH - will increase. B.) H 3 O + will increase. OH - will decrease. C.) H 3 O + will decrease. OH - will increase. D.) H 3 O + will decrease. OH - will decrease.

5 Which ion will increase if an ACID is dissolved in the water? How will the concentration of the other ion respond? A.) H 3 O + will increase. OH - will increase. B.) H 3 O + will increase. OH - will decrease. C.) H 3 O + will decrease. OH - will increase. D.) H 3 O + will decrease. OH - will decrease.

6 When a substance dissolves in water and causes the H 3 O + 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 H 3 O + concentration will decrease. This signals that the substance is a BASE.

7  NOTE : H + = H 3 O +  Let’s look at the 19-1 Practice Problems in your practice packet. We’ll solve numbers 1 and 2 together. 1. What is the concentration of OH - ions in saturated limewater if [H 3 O + ] = 3.98x M? Is the limewater acidic, basic, or neutral? 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?

8  What is the concentration of OH - ions in saturated limewater if [H 3 O + ] = 3.98x M? Is the limewater acidic, basic, or neutral?  If the problem involves OH - and H 3 O + ions, then you’ll use the k w equation to solve.  [H 3 O + ][OH - ]=1.ox  [3.98x ][OH - ]=1.0x  [OH - ]= M  The OH- value is larger so limewater is a base. ▪ H 3 O + = 3.98x vs OH - =0.0251

9  What is the concentration of H 3 O + ions in a wheat flour and water solution is [OH - ] = 1.0x10 -8 M? Is wheat flour and water acidic, basic, or neutral?  If the problem involves OH - and H 3 O + ions, then you’ll use the k w equation to solve.  [H 3 O + ][OH - ]=1.ox  [H 3 O + ][1.0x10 -8 ]=1.ox  [H 3 O + ]=1.0x10 -6 M  The H 3 O + value is larger so wheat flour is acidic.

10 What is the concentration OH - ions in a potato and water solution if [H 3 O + ] = 1.6x10 -6 M? Are potatoes and water acidic, basic, or neutral? A.) [OH - ] = 1.6x ; basic B.) [OH - ] = 1.6x ; acidic C.) [OH - ] = 6.3x10 -9 ; basic D.) [OH - ] = 6.3x10 -9 ; acidic

11 What is the concentration OH - ions in a potato and water solution if [H 3 O + ] = 1.6x10 -6 M? Are potatoes and water acidic, basic, or neutral? A.) [OH - ] = 1.6x ; basic B.) [OH - ] = 1.6x ; acidic C.) [OH - ] = 6.3x10 -9 ; basic D.) [OH - ] = 6.3x10 -9 ; acidic SET UP: [1.6x10 -6 ][OH - ] = 1.0x10 -14

12 What is the concentration of H 3 O + ions in 0.1M ammonia if [OH - ] = 1.26x10 -3 M? Is ammonia acidic, basic, or neutral? A.) [H 3 O + ] = 7.94x ; acidic B.) [H 3 O + ] = 7.94x ; basic C.) [H 3 O + ] = 1.26x ; acidic D.) [H 3 O + ] = 1.26x ; basic

13 What is the concentration of H 3 O + ions in 0.1M ammonia if [OH - ] = 1.26x10 -3 M? Is ammonia acidic, basic, or neutral? A.) [H 3 O + ] = 7.94x ; acidic B.) [H 3 O + ] = 7.94x ; basic C.) [H 3 O + ] = 1.26x ; acidic D.) [H 3 O + ] = 1.26x ; basic SET UP: [H 3 O + ][1.26x10 -3 ] = 1.0x10 -14

14  Complete 5-10 of the 19-1 Practice Problems before class tomorrow.

15  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  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. pH = O 10,000,000x pH = 1 1,000,000x pH = 2 100,000x pH = 3 10,000x pH = x pH = 5 100x pH = 6 10x pH = 7 NEUTRAL pH = 8 10x pH = 9 100x pH = x pH = 11 10,000x pH = ,000x pH = 13 1,000,000x pH = 14 10,000,000x

17  pH = -log[H + ] OR pH = -log[H 3 O + ]  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  Let’s look at the 19-1 Practice Problems in your practice packet again. 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? 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?

19 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 ]=1.0x  [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 12. In a sample of bananas and water, it is found that [H 3 O + ] = 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  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  Complete #13-#20 of the 19-1 Practice Problems before class tomorrow.

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

24  Examples from page in textbook. 32. 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 a. Calculate the pH if pOH= 4.32.

26 b. Calculate the pH if pOH = 8.90.

27 c. Calculate the pH if the pOH = 1.81.

28 d. Calculate the pH if the pOH = 13.1.

29  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. a. [H+] = 1.00x10 -7 M b. [OH-] = 4.39x10 -5 M c. [H+] = 4.29x M d. [OH-] = 7.36x10 -2 M We’ll check answers with the remote in a moment.

30 What is the pH when the [H+] = 1.00x10 -7 M? (pg.590 #33 a)

31 What is the pH is the [OH-] = 4.39x10 -5 M? (pg. 590 #33 b)

32 What is the pOH when the [H+] = 4.29x M? (pg. 590 #33 c)

33 What is the pOH if the [OH - ] = 7.26x10 -2 M? (pg. 590 #33 d)

34  Page  7-12 (skip 11c)  22 a and c  23 a and c  24 b  25 b   34-35


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