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Acids and Bases
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Solutions• homogeneous mixtures in which
one substance is dissolved into another
• the “solute” dissolves in the “solvent”
• example: Kool-Aid - water is the solvent, the drink mix is the solute
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Molarity• Molarity of a solution is equal to the
number of moles of solute divided by the number of liters of solution
• M = mol/L• New symbol [square brackets]
[H+] = molarity of H+ ions• The larger the molarity, the more
concentrated the solution
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Concentrated• In a concentrated solution, the
amount of solute is large compared to the amount of solvent it is dissolved in
• Ex: juices, detergents
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Dilute• In a dilute solution, there is
much more solvent than solute• Solutions are “diluted” by
adding more solvent• 0.5M HCl is more dilute than
2.0M HCl
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Electrolytes• Substances that, when dissolved in
water, produce aqueous solutions that will conduct electricity
• Strong electrolytes release many ions• Many ionic compounds
• Weak electrolytes release few ions
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Properties of acids• React with most metals to produce
H2(g)
• react with carbonates to produce CO2
• taste sour• damage living tissues• pH 0 - 7• neutralize bases
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Common acids• Acid formulas – start with H• HCl – hydrochloric acid• H2SO4 – sulfuric acid• HNO3 – nitric acid• H3PO4 – phosphoric acid• HC2H3O2 – acetic acid
• Also written CH3COOH
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What is an acid?• Many definitions are used• Arrhenius acid: a substance
that produces H+ ions in water
• Then, H2O + H+ H3O+
• H3O+ = hydronium ion
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Acid StrengthCompare the difference in these two
statements:
1) The more H+ ions in the water, the more acidic the solution
2) The more H+ ions a compound produces, the stronger the acid
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Acid Strength• Strong acids release all of their H+ ions
• [strong acid] = [H+]• Strong acids are strong electrolytes
• Weak acids hold on to most of their H+ ions • [weak acid]>>>[H+]• Weak acids are weak electrolytes• Weak acids reach equilibrium with
“neutralization” products
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Don’t get confused!• A solution of a strong acid can
be less acidic that a solution of a weak acid!
• IF: the strong acid solution is very dilute and the weak acid is concentrated!
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Properties of bases• React with fats and oils to produce
soap• feel slippery• taste bitter• damage living tissues• pH 7 - 14• neutralize acids
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What is a base?• Commonly called “antacids”• Arrhenius base:
• a substance that produces OH- (hydroxide) ions when added to water
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Common basesThere are three common varieties of bases:
1) Hydroxide compounds (OH-) ex: NaOH, Ba(OH)2
2) Carbonates (CO32-) and
bicarbonates (HCO3-)
ex: Na2CO3, NaHCO3, CaCO3
3) Ammonia (NH3) and amines
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Hydroxide bases
• Release hydroxide ions directly into the water
• NaOH(s) Na+(aq)+OH-
(aq)
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Carbonates and bicarbonates
• React with water to produce hydroxide ions
• CO32- + H2O HCO3
- + OH-
• HCO3- + H2O H2CO3+OH-
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Ammonia and amines
• React with water to produce hydroxide ions
• NH3 + H2O NH4+ + OH-
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Chemical indicators• Phenolphthalein
• acids = colorless
• bases = pink
• Litmus• acids = red
• bases = blue
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Autoionization of water Water molecules can react with
each other H2O + H20 H3O+ + OH-
At 25ºC, [H3O+] = [OH-]
[H2O] is a constant
Kw = [H3O+] [OH-] = 1x10-14
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Let’s use [H+] instead of [H3O+] Pure water is neutral
[H+] = [OH-]
If [H+] > [OH-], the solution is acidic
If [H+] < [OH-], the solution is basic
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pH scale• Used to indicate the acidity or
“basicity” of a solution• tells how strongly acidic a solution is -
NOT how strong an acid is!• Think pH as “parts H+”• the lower the pH, the more H+’s, the
more acidic the solution
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pH calculation
pH = -log [H+]
[H+] = 10-pH
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pH scale The pH is the measurement
of how many H+’s are in the water – NOT a measure of if the H+’s came from a “strong” or “weak” acid!!!
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pH scale• 0 - 2
• strongly acidic• 2 - 4
• moderately acidic
• 4 - 7• weakly acidic
• 14 - 12• strongly basic
• 12 - 10• moderately
basic• 10 - 7
• weakly basic
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pOH calculation
pOH = -log [OH-]
[OH-] = 10-pOH
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pH & pOH relationship
In pure water at 25°C: [H+] = 1x10-7M
[OH-] = 1x10-7M
Therefore, [H+] x [OH-] = 1x10-14
And pH + pOH = 14
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Arrhenius Neutralization
Works for the reaction of a strong acid with a strong base
Remember – acid (or base strength) has to do with how much of the acid (or base) ionizes in water, not directly how many H+ or OH- are produced
100% ionization = “strong”
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Arrhenius NeutralizationHydroxide base – general form• Acid + Base Salt + H2O
• what’s actually happening?• H+ + OH- H2O
• anion from acid + cation from base = salt
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Arrhenius Neutralization
Examples with a hydroxide base
NaOH + HCl NaCl + H2O
3H2SO4 + 2Al(OH)3 Al2(SO4)3 + 6H2O
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Arrhenius Neutralizationcarbonate base – general form• Acid + Base Salt + H2O + CO2
• what’s actually happening?• 2H+ + CO3
2- H2CO3
• H2CO3 H2O + CO2
• anion from acid + cation from base = salt
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Arrhenius Neutralization
Examples with a carbonate base
CaCO3 + 2 HCl CaCl2 + H2O + CO2
H2SO4 + NaHCO3 Na2SO4 + H2O + CO2