Presentation on theme: "Additional Aspects of Aqueous Equilibria"— Presentation transcript:

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

Kb for Some Common Weak Bases
Many students struggle with identifying weak bases and their conjugate acids.What patterns do you see that may help you? Base Formula Conjugate Acid Kb Ammonia   NH3  NH4+  1.8 x 10-5   Methylamine  CH3NH2  CH3NH3+  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   Hydrazine H2NNH2  H2NNH3+    3.0 x 10-6   Aniline  C6H5NH2   C6H5NH3+    3.8 x 10-10   Pyridine  C5H5N   C5H5NH+    1.7 x 10-9

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 NOT endeavor to make this complicated!)

Buffered Solutions A solution that resists a change in pH when either hydroxide ions or protons are added. Buffered solutions contain either: A weak acid and its salt A weak base and its salt

Acid/Salt Buffering Pairs
The salt will contain the anion of the acid, and the cation of a strong base (NaOH, KOH) Weak Acid Formula of the acid Example of a salt of the weak acid  Hydrofluoric  HF   KF – Potassium fluoride   Formic   HCOOH   KHCOO – Potassium formate   Benzoic   C6H5COOH   NaC6H5COO – Sodium benzoate  Acetic   CH3COOH   NaH3COO – Sodium acetate   Carbonic   H2CO3   NaHCO3 - Sodium bicarbonate  Propanoic   HC3H5O2    NaC3H5O2  - Sodium propanoate  Hydrocyanic   HCN   KCN - potassium cyanide

Base/Salt Buffering Pairs
The salt will contain the cation of the base, and the anion of a strong acid (HCl, HNO3) Base Formula of the base Example of a salt of the weak acid Ammonia   NH3  NH4Cl - ammonium chloride  Methylamine  CH3NH2  CH3NH2Cl – methylammonium chloride  Ethylamine  C2H5NH2  C2H5NH3NO3 -  ethylammonium nitrate  Aniline  C6H5NH2  C6H5NH3Cl – aniline hydrochloride  Pyridine  C5H5N    C5H5NHCl – pyridine hydrochloride

Titration of an Unbuffered Solution
A solution that is 0.10 M CH3COOH is titrated with 0.10 M NaOH

Titration of a Buffered Solution
A solution that is 0.10 M CH3COOH and 0.10 M NaCH3COO is titrated with 0.10 M NaOH

Comparing Results Buffered Unbuffered

Comparing Results Unbuffered Buffered
In what ways are the graphs different? In what ways are the graphs similar?

Henderson-Hasselbalch Equation

Weak Acid/Strong Base Titration
Endpoint is above pH 7 A solution that is 0.10 M CH3COOH is titrated with 0.10 M NaOH

Strong Acid/Strong Base Titration
Endpoint is at pH 7 A solution that is 0.10 M HCl is titrated with 0.10 M NaOH

Strong Acid/Strong Base Titration
A solution that is 0.10 M NaOH is titrated with 0.10 M HCl Endpoint is at pH 7 It is important to recognize that titration curves are not always increasing from left to right.

Strong Acid/Weak Base Titration
A solution that is 0.10 M HCl is titrated with 0.10 M NH3 Endpoint is below pH 7

Selection of Indicators

Some Acid-Base Indicators
pH Range in which Color Change Occurs Color Change as pH Increases Crystal violet Thymol blue Orange IV Methyl orange Bromcresol green Methyl red Chlorophenol red Bromthymol blue Phenol red Neutral red Thymol blue Phenolphthalein Thymolphthalein Alizarin yellow Indigo carmine yellow to blue red to yellow red to yellow red to yellow yellow to blue red to yellow yellow to red yellow to blue yellow to red red to amber yellow to blue colourless to pink colourless to blue yellow to blue blue to yellow

pH Indicators and their ranges

Ksp Values for Some Salts at 25C
Name Formula Ksp  Barium carbonate   BaCO3   2.6 x 10-9   Barium chromate   BaCrO4   1.2 x 10-10   Barium sulfate   BaSO4   1.1 x 10-10   Calcium carbonate   CaCO3   5.0 x 10-9   Calcium oxalate   CaC2O4   2.3 x 10-9   Calcium sulfate   CaSO4   7.1 x 10-5   Copper(I) iodide   CuI   1.3 x 10-12   Copper(II) iodate   Cu(IO3)2   6.9 x 10-8   Copper(II) sulfide   CuS   6.0 x 10-37   Iron(II) hydroxide   Fe(OH)2   4.9 x 10-17   Iron(II) sulfide   FeS   6.0 x 10-19   Iron(III) hydroxide   Fe(OH)3   2.6 x 10-39   Lead(II) bromide   PbBr2   6.6 x 10-6   Lead(II) chloride   PbCl2   1.2 x 10-5   Lead(II) iodate   Pb(IO3)2   3.7 x 10-13   Lead(II) iodide   PbI2   8.5 x 10-9   Lead(II) sulfate   PbSO4   1.8 x 10-8  Name Formula Ksp  Lead(II) bromide   PbBr2   6.6 x 10-6   Lead(II) chloride   PbCl2   1.2 x 10-5   Lead(II) iodate   Pb(IO3)2   3.7 x 10-13   Lead(II) iodide   PbI2   8.5 x 10-9   Lead(II) sulfate   PbSO4   1.8 x 10-8   Magnesium carbonate   MgCO3   6.8 x 10-6   Magnesium hydroxide   Mg(OH)2   5.6 x 10-12   Silver bromate   AgBrO3   5.3 x 10-5   Silver bromide   AgBr   5.4 x 10-13   Silver carbonate   Ag2CO3   8.5 x 10-12   Silver chloride   AgCl   1.8 x 10-10   Silver chromate   Ag2CrO4   1.1 x 10-12   Silver iodate   AgIO3   3.2 x 10-8   Silver iodide   AgI   8.5 x 10-17   Strontium carbonate   SrCO3   5.6 x 10-10   Strontium fluoride   SrF2   4.3 x 10-9   Strontium sulfate   SrSO4   3.4 x 10-7   Zinc sulfide   ZnS   2.0 x 10-25

Solving Solubility Problems
For the salt AgI at 25C, Ksp = 1.5 x 10-16 AgI(s)  Ag+(aq) + I-(aq) I C E O O +x +x x x 1.5 x = x2 x = solubility of AgI in mol/L = 1.2 x 10-8 M

Solving Solubility Problems
For the salt PbCl2 at 25C, Ksp = 1.6 x 10-5 PbCl2(s)  Pb2+(aq) + 2Cl-(aq) I C E O O +x +2x x 2x 1.6 x 10-5 = (x)(2x)2 = 4x3 x = solubility of PbCl2 in mol/L = 1.6 x 10-2 M

Solving Solubility with a Common Ion
For the salt AgI at 25C, Ksp = 1.5 x 10-16 What is its solubility in 0.05 M NaI? AgI(s)  Ag+(aq) + I-(aq) I C E O 0.05 +x 0.05+x x 0.05+x 1.5 x = (x)(0.05+x)  (x)(0.05) x = solubility of AgI in mol/L = 3.0 x M

Precipitation and Qualitative Analysis

Complex Ions A Complex ion is a charged species composed of:
1. A metallic cation 2. Ligands – Lewis bases that have a lone electron pair that can form a covalent bond with an empty orbital belonging to the metallic cation

NH3, CN-, and H2O are Common Ligands

Coordination Number Coordination number refers to the number of ligands attached to the cation 2, 4, and 6 are the most common coordination numbers Coordination number Example(s) 2 Ag(NH3)2+ 4 CoCl Cu(NH3)42+ 6 Co(H2O) Ni(NH3)62+

Complex Ions and Solubility
AgCl(s)  Ag+ + Cl- Ksp = 1.6 x 10-10 Ag+ + NH3  Ag(NH3) K1 = 2.1 x 103 Ag(NH3)+ NH3  Ag(NH3) K2 = 8.2 x 103 AgCl + 2NH3  Ag(NH3)2+ + Cl- K = KspK1K2

Similar presentations