6.4- Explaining Acids and Bases
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Transcript of 6.4- Explaining Acids and Bases
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6.4- Explaining Acids and Bases
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Arrhenius’ TheoryArrhenius’ Theory
acids ionize in water to produce hydrogen ionsbases dissociate in water to produce hydroxide ions
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Arrhenius Theory WeaknessesArrhenius Theory Weaknesses
does not explain why: NH3(aq) acts as a base, or why CO2(g) can act as an acid some gases like sulfur dioxide and nitrogen dioxide produce acidic solutions
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some substances act as both acids and bases
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Revised Arrhenius TheoryRevised Arrhenius Theory
includes water in the reactionacids react with water to produce hydronium (H3O+
(aq))
HCl(aq) + H2O(l) ---> H3O+(aq) + Cl-
(aq)
hydronium is a hydrogen ion bonded onto a water molecule
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..
bases are substances that react with water to produce hydroxide ions. This explains why ammonia acts as a base.
NH3(aq) + H2O(l) ---> OH-(aq) + NH4
+(aq)
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also explains why molecules such as CO2(g), SO2(g), and NO2(g)
act as acids.Two step reaction:
CO2(g) + H2O(l) ---> H2CO3(aq)
H2CO3(aq) + H2O(l) ---> H3O+(aq)
+ HCO3-(aq)
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also explains why some ions can act as both acids and bases.
eg. HCO3-(aq) and HPO4
2-(aq)
HCO3-(aq) + H2O(l) ---> H3O+
(aq) + CO32-
(aq)
HCO3-(aq) + H2O(l) ---> OH- (aq)+ H2CO3(aq)
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Neutralization ReactionWe have seen neutralization reactions to look
like thisHCl(aq) +NaOH(aq) NaCl(aq) +H2O(l)
According to the modified Arrehius theory, we can now state that neutralization is the reaction between hydronium ions ( from the acid) and hydroxide ions ( from the base) to produce water
H3 O+ (aq) +OH- (aq) 2H2 O(l)
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AssignmentRead page 248 -253Do page 251 #1,2Do page 253 #4,5,6