Chapter 9 Section 1. D12 - Explain the chemical composition of acids and bases, and explain the...
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Transcript of Chapter 9 Section 1. D12 - Explain the chemical composition of acids and bases, and explain the...
![Page 1: Chapter 9 Section 1. D12 - Explain the chemical composition of acids and bases, and explain the change of pH in neutralization reactions.](https://reader035.fdocuments.us/reader035/viewer/2022062516/56649dbd5503460f94ab0573/html5/thumbnails/1.jpg)
Acids, Bases, and pHChapter 9Section 1
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D12 - Explain the chemical composition of acids and bases, and explain the change of pH in neutralization reactions.
D12
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What do you know about acids? Can you name some acids? Have you ever had lemonade? The juice of
a lemon is an acid. So, this means that not all acids are alike, since you can safely drink lemonade, but not some other acids.
Acids
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Acids are compounds, which means that they are made of more than one type of element.
One of the elements is always HYDROGEN.
Properties:◦Taste sour◦They will turn blue litmus paper red◦They will conduct electric current◦They are corrosive◦They can sting in an open cut (weaker acids),
or can damage your skin (stronger acids)
So, what are acids?
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When dissolved in water, they ionize.
This means that they split apart into the ions that make up the acid. H+ is ALWAYS formed.
HCl H+ + Cl-
One of the ions formed is the Hydrogen or H+ ion
This can attach to the water molecules to form hydronium ions, H3O+
H20 + H+ H3O+
How do acids work?
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Strong acids ionize completely
Each molecule splits into its ionsThis makes a high concentration of hydrogen and hydronium ions in the liquid.
Weak acids do not ionize completely.This makes a lower concentration of hydronium ions in the liquid.
Strong vs. Weak Acids
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Which of the following "molecular" pictures best represents a concentrated solution of
the weak acid HA?
You try …
A B
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Since there is complete ionization in water, this is a strong acid
An electrolyte is a liquid which can conduct electricity
Nitric Acid conducts electricity well, which means it is a strong electrolyte
HNO3 + H2O H3O+ NO3-
Nitric Acid
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This is an example of a weak acid
Weak acids do not conduct electricity well
This means that they are weak electrolytes
CH3COOH + H2O H3O + CH3COO-
Acetic Acid
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Acids are corrosive They can damage living tissues Acidic vapors can be harmful to eyes,
mouth and lungs Wear safety goggles, gloves, lab apron Overall, be careful!
Acid Safety
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Bases!
What’s next?
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What do you know about bases? Can you name some bases? Do you use soaps or detergents? These are
bases. Like acids, not all bases are alike.
Bases
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A base is a compound that increases the number of hydroxide ions (OH-) when mixed with water.
Properties: A basic solution tastes bitter. A basic solution feels slippery. They will turn red litmus paper blue. Strong bases can also damage the skin.
So, what are bases?
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Like acids, when bases dissolve in water, they ionize.
This means that they split apart into the ions that make up the base.
NaOH Na+ + OH-
Note: Not all bases contain OH-. Some will react with water to form the hydroxide ion
NH3 + H20 NH4+ + OH-
How do bases work?
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These work in a way that is similar to acids.
Strong bases cause a high concentration of OH- ions in the solution.
Weak bases cause a low concentration of OH- ions in the solution.
Strong and Weak Bases
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Like acids, bases are corrosive and can damage living tissues
Wear safety goggles, gloves, and a lab apron!
Base Safety
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How do determine if something is an acid or a base?
How do we measure acid and base concentration or strength?
What’s next?
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Read pages 293-297.
Homework
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Using Indicators with Acids and Bases
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You can determine if a substance is an acid or base by using an indicator.
INDICATOR - A substance that changes color in the presence of an acid or a base.
Indicators measure the level of hydronium ions. This level determines if a substance is acidic or basic.
Detecting Acids and Bases
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Cabbage juice can be used as an indicator.
Litmus paper is a common indicator. Litmus strips are small pieces of paper that are treated with a substance that changes color when exposed to acids and bases
An acid turns blue litmus paper red A base turns red litmus paper blue
Indicators
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Litmus papers only function to let you know if a substance is acidic or basic.
They do not indicate strength or weakness of the solution.
To determine how acidic or basic a solution is, we use pH values.
pH is the measure of the concentration of hydronium ions in a solution.
More specific indicators
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0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
ACIDIC BASIC
NEUTRAL
The pH Scale
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0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
ACID BASE
NEUTRAL
The pH Scale
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Ion
Con
cen
trati
on
Ion
Con
cen
trati
on
pH Scale
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Neu
tral
P
ure
H2O
[H+] [OH-]
Acids Bases
Stronger Weaker Weaker Stronger
Acid – substance that produces H+ ions in aqueous
solution
Base – substance that produces OH-
ions in aqueous solution
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Question #1Lemon juice has a pH of 2.2. Is it an acid or a base?
Which does it contain, hydronium ions or hydroxide ions?
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Question #2Detergents such as Tide have a pH of about 10. Is Tide an acid or a base?
Which does it contain, hydronium ions or hydroxide ions?
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Question #3 Seawater has a pH of 8.2. Is seawater an acid or a base?
Which does it contain, hydronium ions or hydroxide ions?
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Question #4The inside of your mouth has a pH of 7. Is it an acid or a base?
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Question #5How do you think we came up with the term “acid rain”?
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Read pages 297-300
Homework