chapter 17 acids and bases
DESCRIPTION
Chapter 17 Acids and Bases. Necessary Terminology to Begin. Hydronium = H 3 O + ( aq ) or H + ( aq ) Hydroxide = OH - ( aq ) Neutral Water = Equal amounts of above. General Info Bases. Taste Bitter to the taste React with our skin to form soap (so it feels soapy) - PowerPoint PPT PresentationTRANSCRIPT
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Chapter 17 Acids and Bases
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Necessary Terminology to Begin
Hydronium = H3O+ (aq) or H+ (aq)
Hydroxide = OH- (aq)
Neutral Water = Equal amounts of above
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General Info Bases
Taste Bitter to the taste React with our skin to form soap (so it
feels soapy) React with oils and greases (so often
used in cleaning products (ammonia) Can cause dyes to change color. Electrolytes Corrosive
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General Info about Acids
Taste sour Corrosive Electrolytes Attack skin by dissolving fatty acids.
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Common Acids and Bases
Can you name some?
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Common
Sulfuric (Batteries in Car) Nitric (Explosives and Fertilizers
Production) Hydrochloric (Steel Industry (Pickling))
Also called Muriatic
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Common
Aluminum Hydroxide (Deodorant) Magnesium Hydroxide (Laxative) Ammonia (Cleaner) Cough Syrups (taste awful without
flavoring)
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What is an Acid and Base?
3 different definitions that describe what Acids and Bases are Arrhenius Acids and Bases Bronsted-Lowry Acids and bases Lewis Acids and Bases
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Arrhenius Background
His theory defined an acid as any substance that when added to water increases the hydronium ion concentration
Bases as any substance when added to water that increase the hydroxide ion concentration.
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Bronsted Acid and Bases
The Bronsted definition of an acid comes from a man from Denmark who made his proposal in 1923. His theory helped to overcome the shortcomings of the Arrhenius definition by allowing us to describe solutions which were not aqueous.
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Bronsted Acids and Bases
His definition has acids as hydrogen donors and bases as hydrogen acceptors.
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In Summary (Acids)
An Arrhenius acid generates hydronium ions in water.
A Bronsted acid donates hydrogens
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In Summary (Bases)
An Arrhenius base generates hydroxide ions in water
A Bronsted base accepts protons
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Practice Identifying
On the following slides, identify the acid and base (forward reaction) and then whether each acid/base definition works
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Questions
CH3COOH (aq) + H2O (L) CH3COO- (aq) + H3O+ (aq)
HCl (aq) + NH3 (aq) NH4+ (aq) + Cl-
NH3 (aq) + H2O (L) NH4+ (aq) + OH- (aq)
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Amphoteric
A substance that can act as an acid or a base
Water and Ammonia are common examples
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Nomenclature
Throw as many hydrogen’s onto the anion/polyatomic ion and change the ending from ate to ic and ite to ous. With the exception the halogens (Add hydrochloric acid = HCl)
Perchlorate (ClO4-1) becomes
Perchloric Acid (HClO4)
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Nomenclature
Nitrate (NO3-1) becomes Nitric Acid
(HNO3) Sulfite (SO3
-2) becomes Sulfurous Acid (H2SO3)
Also: When writing the formula, if it is an acid, the H is placed at the beginning to denote that the chemical is an acid.
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Major Ideas
Strong and Weak Acids and Bases Conjugate Acids and Bases Bond Strength Acid/Base Equilibrium
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What are Strong Acids/Bases?
Strong acids and bases fully ionize when placed in water.
The Unionized from of the acid is not present. There is no equilibrium, Strong acids and bases are completion reactions in water. HCl (aq) + H2O (l) H3O+ (aq) + Cl- (aq)
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If you take more chemistry, you will need to know these
There are 6 strong acids Nitric Acid (HNO3) Sulfuric Acid (H2SO4) PerChloric Acid (HClO4) HydroBromic Acid (HBr) HydroChloric Acid (HCl) HydroIodic Acid (HI)
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Strong Acids
Every one of those, when placed in water, will ionize and all you will have is Hydronium and the Anion. HCl (aq) + H2O (l) H3O+ (aq) + Cl- (aq) Acid + Water Hydronium + Anion
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Strong Bases
A strong base is any Alkali Metal with a Hydroxide.
Such as: Sodium Hydroxide (NaOH), Potassium Hydroxide (KOH),
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Big Idea behind Strong Acids
If 1,000,000 moleculesof HCl are placed into 1.0 L of water, the Concentration of Hydronium is equal to the concentration of the Strong Acid placed into the solution.
The concentration of Hydronium is 1,000,000 molecules in 1.0 L in this example.
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Conjugate Acids/Bases
When an Acid gives up its proton, the molecule left (minus a hydrogen) is called a conjugate base.
The conjugate base has a negative charge and, being negative, has the ability to attract a nearby hydrogen (which is positive) to bond to it.
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Conjugate Acids/Bases
When a Base receives a proton, the molecule (plus a hydrogen) is called a conjugate acid.
The conjugate acid has a positive charge and is looking to give up its positive charge to another molecule.
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Conjugate Acids/Bases
Summarized Conjugate Acid An acid that forms
when a base gains a proton Conjugate Base A base that forms
when an acid loses a proton
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Example
Acid Base HC2H3O2 (aq) + H2O C2H3O2
- (aq) + H3O+ (aq) Conj. Base Conj. Acid
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Example
Base Acid NH3 (aq) + H2O (l) NH4
+ (aq) + OH- (aq) Conj. Acid Conj. Base
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Practice
Questions What is the conjugate Base of the
following Acids? HCl H2SO4
Hydronium Ammonium (NH4+)
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Practice
Label the following as Acid/Base/CB/CA
HF + H2O F- + H3O+
CH3O- +H2O CH3OH +OH-
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What are Weak Acids/Bases?
Weak acids and bases partially ionize when placed into water. An equilibrium is established where the Hydrogens are fought over (who gets to have the hydrogen?).
Acetic acid (HC2H3O2) when placed into water partially ionizes.
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Weak Acid/Base Example
Weak Acid HC2H3O2 (aq) + H2O C2H3O2
- (aq) + H3O+ (aq) Weak Base
NH3 (aq) + H2O (l) NH4
+ (aq) + OH- (aq)
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How weak is weak?
If 100 weak acid molecules were put into a solution of water, only about 5 would react.
Most weak acids are found with their hydrogen
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New Ideas
The pH Scale Calculating the Hydronium
Concentration
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pH Scale: Before we start…
Quick Math: The Logarithm Scale On a logarithmic scale, a change in 1
represents a change in 10, a change in 2 represents a change of 100. The Richter Scale (Earthquakes) An
earthquake that registers a 5.0 is 1000x stronger than an earthquake that registers 2.0
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The pH Scale
Is a measure of how many Hydroniums are in the water.
The pH means: Powers of Hydrogen On the Log Scale
A pH of 7 means the concentration of Hydronium is 0.0000001 or 1x10-7
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pH Scale
pH pOH [H3O+] [OH-] 0 14 1 1 x10-14
1 13 0.1 1x10-13
2 12 0.01 1x10-12
3 11 1x10-3 1x10-11
4 10 1 x10-4 1 x10-10
5 9 1 x10-5 1 x10-9
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pH Scale
pH pOH [H3O+] [OH-] 6 8 1 x10-6 1 x10-8
7 7 1 x10-7 1 x10-7
8 6 1 x10-8 1 x10-6
9 5 1 x10-9 1 x10-5
10 4 1 x10-10 1 x10-4
11 3 1 x10-11 1 x10-3
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Hydronium in Distilled WaterpH: Why it adds up to 14
Water self ionizes (to a very small extent)
2 H2O (l) H3O+ (aq) + OH- (aq)
Kw = [H3O+][ OH-] Kw = 1.0 x10-14 (This is a constant)
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The pH scale
When acids are added to water, they add to the hydronium concentration (decreasing the hydroxide concentration)
When bases are added to water, they add to the hydroxide concentration (decreasing the hydronium concentration).
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The pH Scale at neutral
Kw = [OH][H] Kw = (1E-7)(1E-7) = 1E-14 pH = 7 A pH of 7 is considered Neutral (it
contains just as much base as acid)
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Question
Can you have a pH less than 0 and greater than 14?
Yes, a 10.0 Molar HCl solution has a pH of -1
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What is the pH?
A solution has a hydronium concentration of 0.001?
A solution has a hydroxide concentration of 0.00001?
A solution has equal concentrations of hydronium and hydroxide?
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Carbonic Acid Our Blood Buffer
Carbon Dioxide in blood Reacts with water forming Carbonic Acid Same as pop
More Carbon Dioxide = More Acid = Lower pH
After a marathon, many runners have lower pH’s then 7.4. This is because of high carbon dioxide concentrations in the blood.
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Breathing Rate
When you hyperventilate, what happens to the blood pH?
When you breath into a brown bag, what happens to the blood pH?
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Neutralization
Acids and Bases react to neutralize each other Produce a salt and water
HCl + NaOH Water and NaCl
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What is a Titration?
A way to determine the acidity or baseness of a solution You have an unknown solution, you can
use a known concentration of acid to find out what the base concentration is
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What is a Titration?
Let’s say a student puts an unknown amount of NaOH into some water.
You can determine how much NaOH was added by titrating the solution against a known concentration of acid
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Equivalence Point
At the equivalence point, equal amounts of acid and base have been added together, so there are no reactants left.
In the case of adding HCl (a strong acid) to NaOH (a strong base), at the equivalence point, there is only water and salt.
HCl + NaOH NaCl + H2O
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Indicators
Indicators change color at different pH’s and are useful for knowing what the pH of the solution is (they won’t give exact, but they will let you know more or less acidic than some number)
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During a titration, you place indicators into the solution to let you know when the pH has crossed a certain point.
Different titrations have different equivalent points, so choosing an appropriate one is important.
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For a SA and SB reaction, indicator isn’t important.
For WA and WB reactions, it is more important
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Phenolphthalein
The two main differences are the extra H (in acidic solution) in the top left of the molecule, and the bonding of the central carbon