Sodium hydroxide Preferred IUPAC name Sodium hydroxide Systematic name Sodium oxidanide Other names Caustic soda Lye Graphics Source Wikipedia AcidBase Definitions Arrhenius Model ID: 310669
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Slide1
Bases
Sodium hydroxidePreferred IUPAC nameSodium hydroxideSystematic nameSodium oxidanideOther namesCaustic sodaLye
Graphics Source: WikipediaSlide2
Acid/Base Definitions
Arrhenius ModelAcids produce hydrogen ions in aqueous solutionsBases produce hydroxide ions in aqueous solutionsBronsted-Lowry ModelAcids are proton donorsBases are proton acceptorsLewis Acid ModelAcids are electron pair acceptorsBases are electron pair donorsSlide3
Dissociation of Strong Bases
Strong bases are metallic hydroxidesGroup I hydroxides (NaOH, KOH) are very solubleGroup II hydroxides (Ca, Ba, Mg, Sr) are less solublepH of strong bases is calculated directly from the concentration of the base in solutionMOH(s) M+(aq) + OH-(aq)Slide4
Reaction of Weak Bases with Water
The base reacts with water, producing its conjugate acid and hydroxide ion:CH3NH2 + H2O CH3NH3+ + OH- Kb = 4.38 x 10-4 Slide5
K
b for Some Common Weak BasesBaseFormulaConjugate Acid
K
b
Ammonia
NH
3
NH
4
+
1.8 x 10
-5
Methylamine
CH
3
NH
2
CH
3
NH
3
+
4.38 x 10-4 Ethylamine C2H5NH2 C2H5NH3+ 5.6 x 10-4 Diethylamine (C2H5)2NH (C2H5)2NH2+ 1.3 x 10-3 Triethylamine (C2H5)3N (C2H5)3NH+ 4.0 x 10-4 Hydroxylamine HONH2 HONH3+ 1.1 x 10-8 HydrazineH2NNH2 H2NNH3+ 3.0 x 10-6 Aniline C6H5NH2 C6H5NH3+ 3.8 x 10-10 Pyridine C5H5N C5H5NH+ 1.7 x 10-9
Many students struggle with identifying weak bases and their conjugate acids.What patterns do you see that may help you?Slide6
Reaction of Weak Bases with Water
The generic reaction for a base reacting with water, producing its conjugate acid and hydroxide ion:B + H2O BH+ + OH-(Yes, all weak bases do this – DO NOTendeavor to make this complicated!)Slide7
A Weak Base Equilibrium Problem
What is the pH of a 0.50 M solution of ammonia, NH3, Kb = 1.8 x 10-5 ?Step #1: Write the equation for the reactionNH3 + H2O NH4+ + OH-Slide8
A Weak Base Equilibrium Problem
What is the pH of a 0.50 M solution of ammonia, NH3, Kb = 1.8 x 10-5 ?Step #2: ICE it!I
C
E
0.50
0
0
- x
+x
+x
0.50 - x
x
x
NH
3
+ H
2
O
NH
4
+
+ OH
-Slide9
A Weak Base Equilibrium Problem
Step #3: Set up the law of mass action0.50 - xxxEWhat is the pH of a 0.50 M solution of ammonia, NH3, Kb = 1.8 x 10-5 ?NH3 + H2O NH4+ + OH-Slide10
A Weak Base Equilibrium Problem
Step #4: Solve for x, which is also [OH-]0.50 - xxxE[OH-] = 3.0 x 10-3 MNH3 + H2O NH4+ + OH-
What is the pH of a 0.50 M solution of ammonia, NH3, Kb = 1.8 x 10
-5 ?Slide11
A Weak Base Equilibrium Problem
Step #5: Convert [OH-] to pH0.50 - xxxEWhat is the pH of a 0.50 M solution of ammonia, NH3, Kb = 1.8 x 10-5 ?NH3 + H2O NH4+ + OH-