hint: it has to do with chemistry!. ever wonder why water is perfectly neutral? how can we determine...
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HINT: It has to do with chemistry!
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Ever wonder why water is perfectly neutral?
How can we determine it is neutral?
Why is this fact so important for our studies of acids and bases?
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Part I: Water Self IonizesWater acts as both an acid AND a base!
Craziness…I know.
Even when alone, water breaks molecules into ions.
H2O(l) + H2O(l) ↔ H3O+1(aq) + OH-1
(aq)
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The Wonders of HydroniumHydronium ion (H3O+)…water with H+
Can also be written as…H+ which is the same as a proton
4 different ways to write/say the same thing
We LOVE chemistry!
Now let’s eat some marshmallows…and think about where
that H+ comes from…
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Self-Ionization of Water Activity
MaterialsPaper towel2 Large Marshmallows4 Small Marshmallows2 toothpicks
Procedure1. Lay a paper towel on your bench with your seat partner. Lay
the food on it to be sanitary.
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Self-Ionization of Water Activity
Procedure
2. Break the 2 toothpicks in halves to make 4 “bonds.”
3. Make 2 water molecules using the small marshmallows as
“H” and the large marshmallows as “O.” The toothpicks are
the “bonds.”
Remember water’s VSEPR shape.
4. Answer questions #1-2 on your notes.
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Self-Ionization of Water Activity
Procedure5. Now, create the products of the self ionization of water.
6. Answer questions #3-4 on your notes.
7. After answering all questions and participating in the discussion, you may eat your marshmallows …dispose of any waste in the trash can.
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Self-Ionization of Water Activity Answers
Answers to the Discussion Questions1. Reactants and/or left side of the equation2.
3. Hydronium and hydroxide ions.
4. They rearrange to create two water molecules again.
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Side Note!
Anything in the brackets means the “concentration of…” for example…
[“?”]= concentration of tea cup Chihuahuas
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Part II: Kw CalculationsPure water
[H3O+1] = [OH-1]Through experimentation, scientists discovered the concentrations of
both ions
[H3O+] = 1.00 x 10-7 M
[OH-] = 1.00 x 10-7 M* only under room temperature (25°C or 298K)
Multiply these together to discover the equilibrium constant for water (Kw)
Kw=[H3O+]•[OH-]=(1.00x10-7M) • (1.00x10-7M)=1.00x10-14
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To summarize…[H3O+] = 1.00 x 10-7 M
[OH-] = 1.00 x 10-7 M
Kw= 1.00 x 10-14 M
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Kw FormulaKw = [H3O+] • [OH-] = 1.00 x 10-14
Kw formula allows scientists to solve for [H3O+] or [OH-], as long as you know one or the other.
Chemistry is AWESOME!
1.00 x 10-14= [H3O+] • [OH-]
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Part III: Labeling Acids and BasesConcentrations of H+ or OH- determine the type of
solution:
Soln has higher [H3O+] (or [H+]) Acidic
Soln has [H3O+] = [OH-] Neutral
Soln has more [OH-] Basic
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Picture Time!Draw a picture to depict an acidic, basic, and neutral solution.
Only use [H+] and [OH-] in your picturesSee “Neutral” example below.
Acid Neutral Base
H+ H+ OH - H + H+
H+ H+
OH - OH - OH -
OH - OH-
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Example 1The H+ concentration of an aqueous solution is 1.0 • 10-4M,
A. What’s the [OH-]?
B. Is the solution acidic, basic, or neutral?
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Example 2The concentration of a LiOH solution is 2.56 • 10-5M,
A. What’s the [H+]?
B. Is the solution acidic, basic, or neutral?
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HomeworkMake new problems!