acids and bases. solutions homogeneous mixtures in which one substance is dissolved into another the...
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Acids and Bases
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
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
Concentrated• In a concentrated solution, the
amount of solute is large compared to the amount of solvent it is dissolved in
• Ex: juices, detergents
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
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
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
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
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
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
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
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!
Properties of bases• React with fats and oils to produce
soap• feel slippery• taste bitter• damage living tissues• pH 7 - 14• neutralize acids
What is a base?• Commonly called “antacids”• Arrhenius base:
• a substance that produces OH- (hydroxide) ions when added to water
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
Hydroxide bases
• Release hydroxide ions directly into the water
• NaOH(s) Na+(aq)+OH-
(aq)
Carbonates and bicarbonates
• React with water to produce hydroxide ions
• CO32- + H2O HCO3
- + OH-
• HCO3- + H2O H2CO3+OH-
Ammonia and amines
• React with water to produce hydroxide ions
• NH3 + H2O NH4+ + OH-
Chemical indicators• Phenolphthalein
• acids = colorless
• bases = pink
• Litmus• acids = red
• bases = blue
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
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
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
pH calculation
pH = -log [H+]
[H+] = 10-pH
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!!!
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
pOH calculation
pOH = -log [OH-]
[OH-] = 10-pOH
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
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”
Arrhenius NeutralizationHydroxide base – general form• Acid + Base Salt + H2O
• what’s actually happening?• H+ + OH- H2O
• anion from acid + cation from base = salt
Arrhenius Neutralization
Examples with a hydroxide base
NaOH + HCl NaCl + H2O
3H2SO4 + 2Al(OH)3 Al2(SO4)3 + 6H2O
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
Arrhenius Neutralization
Examples with a carbonate base
CaCO3 + 2 HCl CaCl2 + H2O + CO2
H2SO4 + NaHCO3 Na2SO4 + H2O + CO2