1. Acid-Base Reactions Ch. 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
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
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 base:
HC2H3O2(aq)+NaOH(aq)
C2H3O2-(aq)+H2O(l)
HC2H3O2(aq)+OH-(aq)
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
XCO3 or 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?
2 HCl + 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 HBr: NaOH + HBr NaBr + H2O; strong MA= MBVB/VA
 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