Download Reactions, Acids and Bases

Terms
 Acid
 Titration
 Base
 pH
 Indicator
 pOH
Reactions,
Acids and Bases
Chapters 17 & 19
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.
Definitions
 Brønsted–Lowry
 Acid:
Proton donor
 Base: Proton acceptor
Conjugate Acids and Bases:

Reactions between acids and bases always yield
their conjugate bases and acids.
Conjugate Acids and Bases:
Bases react with water to produce hydroxide ion.
Acid and Base Strength

Strong acids/bases are
completely dissociated in
water.

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Their conjugate bases/acids
are relatively weak.
Weak acids/bases only
dissociate partially in water.

Their conjugate bases/acids
are relatively strong.
pH
 In pure water,
pH = 7.00
 Acid = higher [H+] than water,
& pH < 7
+
 Base = lower [H ] than water,
& pH >7.
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.
Calculating [H+]

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Since the pH = -log [H+]
In order to calculate the [H+] you must take
the antilog:
[H+] = antilog (-pH)
[H+] = 10-pH
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.
Indicator

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Red cabbage contains a molecule called flavin.
The color of the juice changes in response to changes
in its hydrogen ion concentration.
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Acids will donate hydrogen ions in a solution and have a low pH (pH
< 7).
Bases accept hydrogen ions and have a high pH (pH > 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.
Group Activity
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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.
Challenge

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It’s 1700
You have an unknown substance
Want to know if it’s 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!!!
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:

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Phenolphthalein – Acidic Form (Colorless)
Phenolphthalein – Basic Form (Magenta)
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.
M=mol / L
M1V1 = M2V2
pH + pOH = 14
pH = -log [H+]
pOH = -log [OH-]
[H+] = 10 ^ -pH
[OH-] = 10 ^ -pOH
Practice time!!!

Get out your textbooks and do Practice
Problems
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Practice Problem 19 (pg 611)
Practice Problem 20 (pg 612)
Practice Problem 21 (pg 614)
Practice Problem 22 (pg 614)