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Acid-Base Reactions Ch. 15

Acid-Base Reactions Ch. 15. Acid-Base Reactions. Neutralization reactions 中和反应 pH is changed Produce a salt and H 2 O Salts are ionic compounds 2 types of Acids Strong and Weak 2 types of Bases Strong and Weak 4 possible combinations of Acids and Bases Strong A + Strong B

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Acid-Base Reactions Ch. 15

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  1. Acid-Base ReactionsCh. 15

  2. Acid-Base Reactions • Neutralization reactions中和反应 • pH is changed • Produce a salt and H2O • Salts are ionic compounds • 2 types of Acids • Strong and Weak • 2 types of Bases • Strong and Weak • 4 possible combinations of Acids and Bases • Strong A + Strong B • Strong A + Weak B • Weak B + Strong B • Weak B + Weak A

  3. Strong Acid + Strong Base • HCl + NaOH NaCl + HOH • Double replacement reaction • Both compounds completely dissociate HCl Cl- + H+ NaOH Na+ + OH- • Complete equation (aq) can be written: H++Cl-+Na++OH-Cl-+Na++H2O • Spectator Ions • Ions that do not take part in the reaction

  4. Net Ionic Equations净离子方程式 1) Write Complete Ionic Equation All soluble compounds are shown as free ions 2) Remove Spectator Ions Ions not directly evolved in the rxn. 3) Balance the remaining rxn.

  5. Strong Acid + Strong Base • What is the net ionic equation: HCl(aq) + NaOH(aq) 1) H+(aq) +Cl-(aq) +Na+(aq) +OH-(aq) Cl-(aq) +Na+(aq) +H2O(aq) 2) H+(aq) +OH-(aq)  H2O(l) • All strong acid and strong base reactions have this as a base net ionic equation KOH(aq)+HNO3(aq)KNO3(aq)+H2O(l) K++OH-+H++NO3- K++NO3-+H2O(l) OH-+H++ H2O(l)

  6. Strong Acid + Weak Base • HCl(aq) + Al(OH)3(s) • Weak bases wont completely dissociate • Cannot write them as ions on reaction side of net ionic equation H+(aq)+Cl-(aq)+Al(OH)3(s)Al+3(aq)+Cl-(aq)+H2O(l) H+(aq)+Al(OH)3(s)Al+3(aq)+H2O(l) • End solution is slightly acidic • What about NH3? • Considered a weak base but has no OH- • Does not produce water • HCl(aq)+NH3(aq)NH4Cl(aq) H+(aq)+Cl-(aq)+NH3(aq)NH4++Cl-(aq) H+(aq))+NH3(aq)NH4+

  7. Weak Acid + Strong Base • HC2H3O2(aq) + NaOH(aq) • Weak acid wont completely dissociate • Wont breakdown into ions on reaction side HC2H3O2(aq) + Na+(aq)+OH-(aq)Na+(aq)+C2H3O2-(aq)+ H2O(l) HC2H3O2(aq) +OH-(aq)C2H3O2-(aq)+ H2O(l) • End solution is slightly basic Weak Acid + Weak Base ???Not clear??? • Both the acid and base are so unreactive there is little change • Not common reaction type in nature

  8. Bronsted-Lowery Acids and Bases • Acids produce H+ ions when added to water • Bases produce OH- ions when added to water HCl(aq)+H2O(l)H3O+(aq)+Cl-(aq) H2O(l)+NH3(aq)NH4+(aq)+OH-(aq) • Acid= Any compound that releases H+ • Base= Any compound that takes H+ • Water can act as an acid or a base • Conjugate Acid/Base • Weak acid or base produced from an acid-base reaction ACID BASE Conjugate acid Conjugate base ACID BASE Conjugate acid Conjugate base

  9. Regulating pH Add a strong base: HC2H3O2(aq)+NaOH(aq) C2H3O2-(aq)+H2O(l) HC2H3O2(aq)+OH-(aq) C2H3O2-(aq)+H2O(l) • Living things interact with acids and bases all the time; their pH must be regulated • Buffer • Solution that adjusts to the addition of acids and bases to slowly change the pH • Free OH- and H+ ions • Weak acid/base + salt of that acid/base NaOH + HC2H3O2H2O + NaC2H3O2 NaC2H3O2 and HC2H3O2 Add a strong acid: NaC2H3O2(aq)+HCl(aq) HC2H3O2(aq)+NaCl(l) C2H3O2-(aq)+H+(aq)HC2H3O2(aq)

  10. Buffers in the Blood • Blood must keep a pH of 7.4 to allow the best exchange of CO2 and O2 • Blood buffer is HCO3-/H2CO3 • Add Base: H2CO3+OH-HCO3-+H2O • Add Acid: HCO3-+H+H2CO3 • What happens when you take in too much CO2? • H2CO3 increases making blood more acidic • What kind of blood pH results in yawning? • Acidic blood; body needs to release large amount of CO2 by taking in large amount of O2

  11. Antacids抗酸剂 • Compound controls acidic pH levels by adding base • 2 types: • Hydroxide Antacids • Low solubility in water • Release OH- to neutralize H+ • Milk of Magnesia (Mn(OH)2) • Carbonate Antacids • XCO3or XHCO3; react with HCl • CaCO3 + 2HClCaCl2 + H2CO3 Breaks down to CO2 and H2O

  12. Titrations滴定 • Test to determine the molarity of an acid or a base • Find the Standard Solution标准溶液 • Process: • Standard solution of an acid/base is slowly added to an acid/base of unknown molarity • When the unknown acid/base is neutral, the [H+]=[OH-] • How do we know the Standard solution is neutral? • pH Indicators酸碱指示剂 • Volume of acid/base used gives us molarity • MAVA = MBVB • End point • Equivalence point • Neutral point

  13. Titrations practice • If 15.0 mL of 0.50 M NaOH is used to neutralize 25.0 mL of HC2H3O2, what is the molarity of the acid solution? NaOH + HC2H3O2 H2O + NaC2H3O2;1:1 ratio • MAVA = MBVB • MA= MBVB/VA = (0.50 M)(15.0 ml)/25.0 ml = 0.30 M • If 25.0 mL of a standard 0.05 M HCl solution is required to neutralize 20.0 mL of a solution of Sr(OH)2, what is the concentration of the base? 2HCl + Sr(OH)2 SrCl2 + 2H2O; 2:1 ratio • MAVA = 2 MBVB • MB = MAVA/2VB = (0.05 M)(25.0 ml)/(2)(20.0 ml) = 0.03 M

  14. Titrations practice • What types of acid-base reactions do these titration graphs show?

  15. Titrations practice • Graphs shows titration of 0.5 M NaOH with 50ml of an unknown acid. After titration NaBr salt crystals were isolated from the solution. a) What is the acid used? Is it strong or weak? b) what is the concentration of the acid used? HBr:NaOH + HBr NaBr + H2O; strong MA= MBVB/VA = (0.5M)(35ml)/50ml = 0.35 M

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