Terms

1
Terms

• Acid
• Base
• Indicator

• Titration
• pH
• pOH

2
Reactions, Acids and Bases

• Chapters 17 19

3
Definitions

• Acid Substance that, when dissolved in water,
  increases the concentration of hydrogen ions.
• Base Substance that, when dissolved in water,
  increases the concentration of hydroxide ions.

4
Definitions

• BrønstedLowry
• Acid Proton donor
• Base Proton acceptor

5
Conjugate Acids and Bases

• Reactions between acids and bases always yield
  their conjugate bases and acids.

6
Conjugate Acids and Bases

• Bases react with water to produce hydroxide ion.

7
Acid and Base Strength

• Strong acids/bases are completely dissociated in
  water.
• Their conjugate bases/acids are relatively weak.
• Weak acids/bases only dissociate partially in
  water.
• Their conjugate bases/acids are relatively strong.

8
pH

• In pure water,
• pH 7.00
• Acid higher H than water, pH lt 7
• Base lower H than water, pH gt7.

9
pH

• pH expresses the acidity of a solution
• pH -log H
• pOH expresses the basicity of a solution
• pOH -log OH-
• NOTE that pH pOH 14.00
• Therefore if you calculate one you can determine
  the other.

10
Calculating H

• Since the pH -log H
• In order to calculate the H you must take the
  antilog
• H antilog (-pH)
• H 10-pH

11
Titration

• Is a method for determining the concentration of
  a solution by reacting a known volume and
  concentration of a solution with the unknown
  solution.

12
Indicator

• Red cabbage contains a molecule called flavin.
• The color of the juice changes in response to
  changes in its hydrogen ion concentration.
• Acids will donate hydrogen ions in a solution and
  have a low pH (pH lt 7).
• Bases accept hydrogen ions and have a high pH (pH
  gt 7).
• Very acidic solutions will turn flavin a red
  color.
• Neutral solutions result in a purplish color.
• Basic solutions appear in greenish-yellow.
• Therefore, it is possible to determine the pH of
  a solution based on the color it turns the flavin
  in red cabbage juice.

13
Group Activity

• Get with your lab partners
• Create some sort of demonstration for the class
  that explains.
• Factors affecting Reaction Rates 17.2 page 536
• It must include the Nature of Reactants,
  Concentration, Surface Area, Temperature and
  Catalysts.
• You must clearly state each topic and give clear
  explanations to receive full credit.
• This will count as a lab grade.

14
Challenge

• Its 1700
• You have an unknown substance
• Want to know if its acidic or basic
• You have 4 known substances to compare
• However, you need some sort of indicator to tell
  you which if it is acidic or basic
• What do you do???
• Go to nature find plants, dissolve your
  substances in them and observe there color!!!

15
Phenolphthalein

• An acid-base indicator is an organic compound
  whose color is sensitive to changes in pH. The
  acid form of the indicator contains an acidic
  hydrogen while the base form
• does not. It is the presence (or absence) of this
  hydrogen atom that determines the color of the
  indicator. Phenolphthalein, a common indicator in
  the chemistry lab, is colorless under acidic
  conditions and bright pink (magenta) under basic
  conditions. The structures of the acidic and
  basic forms of the molecule are shown below
• Phenolphthalein Acidic Form (Colorless)
• Phenolphthalein Basic Form (Magenta)

16
Indicators
Anthocyanin dyes, the organic molecules that give
cabbage its colors, can be used in the chemistry
lab as acid-base indicators. The purpose of this
lab is to prepare a homemade indicator using the
cabbage.
17
Mmol / L M1V1 M2V2 pH pOH 14 pH -log
H pOH -log OH-H 10 -pH OH-
10 -pOH
18
Practice time!!!

• Get out your textbooks and do Practice Problems
• Practice Problem 19 (pg 611)
• Practice Problem 20 (pg 612)
• Practice Problem 21 (pg 614)
• Practice Problem 22 (pg 614)