HINT: It has to do with chemistry!

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?

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)

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…

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.

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.

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.

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.

Side Note!

Anything in the brackets means the “concentration of…” for example…

[“?”]= concentration of tea cup Chihuahuas

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

To summarize…[H3O+] = 1.00 x 10-7 M

[OH-] = 1.00 x 10-7 M

Kw= 1.00 x 10-14 M

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-]

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

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-

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?

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?

HomeworkMake new problems!