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6.4- Explaining Acids and Bases

6.4- Explaining Acids and Bases. Arrhenius’ Theory. acids ionize in water to produce hydrogen ions bases dissociate in water to produce hydroxide ions. Arrhenius Theory Weaknesses. does not explain why: NH 3( aq ) acts as a base, or why CO 2(g) can act as an acid

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6.4- Explaining Acids and Bases

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  1. 6.4- Explaining Acids and Bases

  2. Arrhenius’ Theory • acids ionize in water to produce hydrogen ions • bases dissociate in water to produce hydroxide ions

  3. Arrhenius 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

  4. some substances act as both acids and bases

  5. Revised Arrhenius Theory • includes water in the reaction • acids 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

  6. . • 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)

  7. 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)

  8. also explains why some ions can act as both acids and bases. • eg. HCO3-(aq) and HPO42-(aq) HCO3-(aq) + H2O(l) ---> H3O+(aq) + CO32-(aq) HCO3-(aq) + H2O(l) ---> OH-(aq)+ H2CO3(aq)

  9. Neutralization Reaction We have seen neutralization reactions to look like this HCl(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)

  10. Assignment • Read page 248 -253 • Do page 251 #1,2 • Do page 253 #4,5,6

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