chapter 15
DESCRIPTION
Chapter 15. Applications of Equilibrium. Common Ions. An ion that is present in both An acid and its conjugate base HNO 2 and NaNO 2 A base and its conjugate acid NH 3 and NH 4 Cl This common ion effects the position of the equilibrium and the pH. - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/1.jpg)
Chapter 15
Applications of Equilibrium
![Page 2: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/2.jpg)
Common Ions
• An ion that is present in both
– An acid and its conjugate base
• HNO2 and NaNO2
– A base and its conjugate acid
• NH3 and NH4Cl
• This common ion effects the position of the equilibrium and the pH
![Page 3: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/3.jpg)
• How will the pH of a solution containing 0.10M HNO2 compare to a solution containing 0.10M HNO2 and 0.10M NaNO2? Why?
![Page 4: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/4.jpg)
Points To Remember
• In common ion situations you MUST consider the initial concentrations of any common ions in solution before you begin the problem
• The larger Ka or Kb will govern the equilibrium
![Page 5: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/5.jpg)
• Calculate the pH of a solution containing 0.10M HNO2 and 0.10M NaNO2? (Ka = 4.0x10-4)
![Page 6: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/6.jpg)
Homework
• P. 774 #’s 21,23a&d, 34,36
![Page 7: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/7.jpg)
Buffered Solutions
• Solutions that resists changes in pH when an acid or base is added
• Made of– Weak acid and its conjugate base– Weak base and its conjugate acid
• Made by adding both chemicals or reacting
![Page 8: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/8.jpg)
Adding
.1M HF
NaF
![Page 9: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/9.jpg)
Reacting
.1M HF
.1M NaOH
![Page 10: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/10.jpg)
• Determine the pH of a solution made by dissolving NaHCO3 to 0.25M in 0.0233M H2CO3 (Ka = 4.3x10-7)
![Page 11: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/11.jpg)
Henderson-Hasselbalch Equ.
• A way of calculating buffer problems
• ONLY USED 4 BUFFERS!!!!!!
![Page 12: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/12.jpg)
HA H+ + A-
][
]][[
HA
AHKa
][
][log
Acid
BasepKapH
![Page 13: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/13.jpg)
• Determine the pH of a solution made by dissolving NaHCO3 to 0.25M in 0.0233M H2CO3 (Ka = 4.3x10-7) Use H-H Equ.
![Page 14: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/14.jpg)
How Do Buffers Work
• Strong acid or base is not allowed to build up in solution
• Strong acid is replaced by weak acid
• Strong base is replaced by weak base
– The strong acid or base reacts completely!!!
– Then equilibrium kicks in
![Page 15: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/15.jpg)
Acidic Buffers
HF H+ + F-
Add NaOH
Add HCl
![Page 16: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/16.jpg)
Basic Buffer
NH3 + H2O NH4
+ + OH-
Add NaOH
Add HCl
![Page 17: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/17.jpg)
• Determine the pH after 0.20 grams of NaOH is added to 500.mL a solution made by dissolving NaHCO3 to 0.25M in 0.0233M H2CO3 (Ka = 4.3x10-7)
![Page 18: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/18.jpg)
What Makes a Good Buffer?
• The best buffers have acids and bases at the same, large concentration
– Added acid or base has little effect on pH
– When the concentrations are the same pH=pKa
![Page 19: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/19.jpg)
Homework
• P. 774 #’s 23d,31,37ab, 40, 42,46,48,49
![Page 20: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/20.jpg)
Titrations
• The controlled addition of a chemical of known concentration to a chemical of unknown concentration
• Known Chemical – Standard or titrant
• Unknown Chemical - Analyte
![Page 21: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/21.jpg)
• Titrations are carried out to the equivalence point– Point when mole ratio of chemicals is reached– Often an invisible point
• Marked by and indicator
• Indicator is a chemical that changes color in different pH’s
• Indicator color change marks the endpoint– Hopefully endpoint and equivalence point are
the same
![Page 22: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/22.jpg)
Titration Curves
• Plotting of the pH of the titration solution as solution is added
• Used as a way of determining equivalence and Ka or Kb values
• Specific ranges for specific acid/base combinations – Strong/Strong or Strong/Weak
![Page 23: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/23.jpg)
Titration Curve HCl vs NaOH
http://www.chemguide.co.uk/physical/acidbaseeqia/phcurves.html
![Page 24: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/24.jpg)
Titration Curve Problems
• Remember the process. Do NOT memorize!
• Treat each step as a separate problem
– For Strong/Strong systems just stoichiometry
• For Strong/Weak First stoichiometry then equilibrium
![Page 25: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/25.jpg)
Strong Acid / Strong Base
• Beginning – Just the pH of the chemical you have
• Before Equivalence – Stoichiometry
• Equivalence – pH is 7.00
• After Equivalence - Stoichiometry
![Page 26: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/26.jpg)
• Strong Acid / Strong Base Titration
#54 page 776
80.0 mL of 0.100M Ba(OH)2 is titrated with 0.400M HCl
0.00 mL
20.0 mL
30.0 mL
40.0 mL
80.0 mL
![Page 27: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/27.jpg)
Weak / Strong Titration
• Beginning – Just the pH of the chemical you have (Might need equilibrium)
• Before Equivalence – Stoichiometry then equilibrium
• Equivalence – pH is NOT 7 – Stoichiometry then equilibrium
• After Equivalence - Stoichiometry
![Page 28: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/28.jpg)
Weak / Strong Combos
• Weak Acid / Strong Base
• Equivalence Point is ABOVE seven– Conjugate base of a weak acid controls pH
• Weak Base / Strong Acid
• Equivalence Point is BELOW seven– Conjugate acid of a weak base controls pH
• At halfway pH = pKa or pOH = pKb!!!!!!!!
![Page 29: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/29.jpg)
Weak Base / Strong Acid Titration
http://www.chemguide.co.uk/physical/acidbaseeqia/phcurves.html
![Page 30: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/30.jpg)
Weak Acid / Strong Base Titration
http://www.chemguide.co.uk/physical/acidbaseeqia/phcurves.html
![Page 31: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/31.jpg)
• Strong Base/ Weak Acid Titration
#55 page 776
100.0 mL of 0.200M Acetic Acid is titrated with 0.100M KOH
0.00 mL
50.0 mL
100.0 mL
200.0 mL
250.0 mL
![Page 32: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/32.jpg)
Homework
• P. 775 #’s 52,53,56
![Page 33: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/33.jpg)
Which Indicator to Use?
• Choosing the appropriate indicator is important when doing titrations
• There are so many good ones to use
• So how does a chemist know???????
![Page 34: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/34.jpg)
Which Indicator to Use?
• Indicators are weak acids and change color with varying pH
• Pick the indicator that changes a little above your calculated equivalence point.
• Pick indicator with pKa value close to equivalence point
• Change color +/- 1 from pKa
![Page 35: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/35.jpg)
![Page 36: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/36.jpg)
Example
• Choose an indicator for the titration of HCl with NH3 pH=5.36
![Page 37: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/37.jpg)
Polyprotic Acids
• These acids have multiple equivalence points
• Carbonic acid has two
• Phosphoric acid has three
• Multiple step points on a titration curve
![Page 38: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/38.jpg)
Diprotic Acid Titration
![Page 39: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/39.jpg)
Molar Mass of an Acid
• You can find the molar mass of an acid by titration too
• Titrate a acid of known mass with a standard to determine number of moles
• Divided grams by moles– Molar Mass
![Page 40: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/40.jpg)
Solubility Equilibrium
• Dissolving is an equilibrium process
• Chemicals that we say are insoluble are actually very slightly soluble– Meaning only a small amount of the solute
dissolves – Concentrations are very small
• 10-5M to 10-20M are common
![Page 41: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/41.jpg)
Solubility Equilibrium
• Iron (II) Sulfide is “insoluble” by solubility rules
• However, it still dissolved to a small extent
• Consider the reaction
FeS(s) Fe+2 + S-2
• Since dissolving is an equilibrium process we can write an equilibrium expression
• Keq = [Fe+2] [S-2]
• FeS is omitted because it is a solid
![Page 42: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/42.jpg)
Solubility Product Constant
• The previous equilibriums expression is a “special” type of equilibrium expression
• Ksp – solubility product constant
• Ksp = [Fe+2] [S-2]– Only used for slightly soluble salts– Never includes the reactants– Ksp’s are very small– Check out the table 15.4 page 753
![Page 43: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/43.jpg)
Ksp Values
• Lead (II) Chloride 2.4X10-4
• Strontium Carbonate 3.8X10-9
• Nickel (II) Hydroxide 5.5X10-16
• Copper (II) Hydroxide 2.2X10-20
• Cadmium Sulfide 8.0X10-28
• Silver Sulfide 6.0X10-51
• And my personal favorite• Bismuth Sulfide 1.6x10-72
![Page 44: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/44.jpg)
Ksp Values
• Q) What does a small Ksp value mean?
• A) Low concentration of ions• Small solubility
• Q) Is the compound with the smallest Ksp the least soluble?
• A) Not necessarily – There are different numbers of ions that changes
the expression
![Page 45: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/45.jpg)
Solubility of Salts
• We can easily compare solubility for salts that have the same # of ions
• When there are the same # of ions the salt with the smallest Ksp is least soluble
• Which salt is least soluble, most soluble AgCl, FeS, BaSO4
– FeS 6.0x10-19 Least soluble– AgCl 1.6x10-10 Most soluble
– BaSO4 1.1x10-10 Middle
![Page 46: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/46.jpg)
Calculating Solubility
• We can calculate solubility of salts and the concentration of the ions in solutions from Ksp
• Deal with saturated solutions– The salt has dissolved as much as it can
• Ksp has been reached
• In saturated solutions the concentrations of the ions are related to the mole ratio
![Page 47: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/47.jpg)
Example• Calculate the solubility of silver chloride
Ksp=1.6x10-10
![Page 48: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/48.jpg)
Example• Calculate the solubility of mercury (II) sulfide
and the concentration of each ion in a saturated solution Ksp=1.6x10-54
![Page 49: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/49.jpg)
Example• Calculate the solubility of calcium phosphate
Ksp=1.3x10-32
![Page 50: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/50.jpg)
Example• A saturated solution of Iron (III) Hydroxide
has a concentration of Fe+3 of 1.8x10-8. What is the Ksp of Iron (III) Hydroxide?
![Page 51: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/51.jpg)
Common Ion Revisited
• Anyone ever have a barium shake for a scan?
• Contains barium sulfate.– Barium ions are very toxic to the body– Treated as calcium
• How can you have fewer barium ions in solution?
• Add Sodium Sulfate
![Page 52: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/52.jpg)
• What is the concentration of barium ions in a saturated solution of barium sulfate?– Ksp = 1.1x10-10
• What is the concentration of barium ions in a when 0.10M Sodium Chloride is added to a saturated solution of barium sulfate
![Page 53: Chapter 15](https://reader035.vdocuments.mx/reader035/viewer/2022062517/56813aa4550346895da29f46/html5/thumbnails/53.jpg)
Precipitation
• If you combine Silver Nitrate with Sodium Chloride will a precipitate always form?
• Only if Ksp is exceeded
• Will a ppt. form if 2x10-5M Silver Nitrate is mixed with 3x10-3M Sodium Chloride?
• Ksp of AgCl is 1.6x10-10
• No