acids & bases. acid/base theory acids and bases are solutions which can be described differently...
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ACID/BASE THEORY
• Acids and bases are solutions which can be described differently by multiple theories.
• So far, we have treated everything that utilizes • “H” as a cation = acid • H3PO4
• “OH” as an anion = base• NaOH
ARRHENIUS THEORY
• The theory that anything capable of producing H+ ions are acids and those producing OH- anions are bases is Arrhenius’ Theory of acids/bases.
• Based on the notion that these substances dissociate in solution into their ions.
• H2SO4 2H+ + SO4-2
H20
BRONSTAD LOWRY ACIDS/BASES
•More general description of acids and bases, incorporates all Arrhenius acid/bases• Acids = H+ donors• Bases = H+ acceptors
Example:NH3 (aq) + H2O (l) NH4
+ (aq) + OH-(aq)
• Would solutions of NH3 be acidic or basic?
CONJUGATE ACIDS/BASES
NH3 (aq) + H2O (l) NH4+ (aq) + OH-(aq)
Conjugate Acid: The compound remaining after H+ acceptance by a base.
NH3 NH4+
Base Conjugate Acid
Conjugate Base: The compound remaining after H+ donation by an acid.
H2O OH-
Acid Conjugate Base
LEWIS ACID/BASES
•Describes Acid/Bases based upon electron donation.• Lewis Acid: A substance that can accept a
pair of electrons to form a covalent bond.• Lewis Base: A substance that can donate a
pair of electrons to form a covalent bond.
H + + OH - H2O
STRENGTH OF ACIDS/BASES
• For this class, we will mostly discuss Arrhenius acid/bases (H+ cation/OH- anion)
• The strength of these solutions is determined by the concentration (Molarity) of H+ or OH- ions in the solution.• Dependent upon…
1) Amount of dissolved solute donating the ion2) Likelihood of ion dissociation
CONCENTRATION OF SOLUTE
• Just like calculating the molarity of non acid/base solutions.• M = mol solute / liter solution
• Example: What is the concentration of a H2SO4
solution if 13.2 g of solute are dissolved in 100mL of di-water?
CALCULATING [H+ ] & [OH-]
•However, we cannot assume the molarity (concentration) of H+ /OH- ions is the same as the molarity of the solution for 2 reasons:
1. Not all acids/bases completely dissociate into their ions.
2. Not all acidic/basic compounds donate 1 ion per molecule
• Complete dissociation: all solute dissociates into ions, meaning the concentration of ions can be calculated with the molar ratio.
HCl H+ + Cl-
1 mol HCl produces 1 mol H+
• So a 0.2M HCl solution would have a H+ concentration of 0.2M as well
DISSOCIATION
COMPLETE DISSOCIATION
• Few acids/bases completely dissociate• If they do, they are termed “Strong Acids/Bases” because they produce high concentrations of their ions upon dissociation.
• Strong Acids (7): HCl, HBr, HI, H2SO4, HNO3, HClO3, HClO4
• Strong Bases (8): LiOH, NaOH, KOH, RbOH, CsOH, Ca(OH)2, Sr(OH)2, Ba(OH)2
CALCULATING ION DONATION
•Not all acids/bases donate 1 H+ or OH- into solution when they dissociate!
•How many ions would the following acids/bases donate if they completely dissociate?
• HBr• Ca(OH)2
• H2SO4
[H+] EXAMPLE
Using the previous H2SO4 example (13.2 g of solute are dissolved in 100mL of di-water), calculate the [H3O+] of the solution.
PARTIAL DISSOCIATION
•Weak acids/bases do not completely dissociate in water. They are called weak, because a lower concentration of H+ or OH- ions results.
• Example: Only about 1% of Phosphoric Acid (H3PO4) dissociates into H+ + H2PO4.
DISSOCIATION OF STRONG & WEAK ACIDS/BASES
• In other words, you would need to know what percentage of an acidic/basic compound is likely to donate its ions into solution in order to calculate the [H+ ] & [OH-].
• For this class, we will be working with strong acids/bases. So complete dissociation (ion donation) can be assumed.
POTENTIAL OF HYDROGEN
• pH = potential of hydrogen
• pH is an expression of the concentration of H+ ions in solution. Since H+ readily reacts with water to form H3O+, we calculate…
pH = −log [H3O+]
[H3O+] = 10-pH
PH & POH
• Just as pH is an expression of the concentration of H+ ions in solution, pOH expresses the concentration of OH- ions in solution…
pOH = −log [OH-][OH-] = 10-pOH
• pH & pOH always add up to 14 and thus are related through the equation:
pH + pOH = 14
PH SCALE
• pH < 7 acidic• pH = 7 neutral• pH > 7 basic
•High [H3O+] acid
• Low [H3O+] base
• [H3O+] = ~1x10-7
neutral
ACID/BASE REACTIONS
• Also known as neutralization reactions, because the pH of the final solution becomes neutralized towards pH=7
• Either [H3O+] or [OH-] is decreased by forming more neutral products.
Acid + Base Salt + Water
ACID/BASE REACTIONS
• 2 Types you will need to know…
1) Acid + Base Salt + H2O
2) Acid + Carbonate Salt + H2O + CO2
ACID/BASE REACTION #1
• Example: Hydrochloric acid reacts with sodium hydroxide.
HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l)
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