CM4106 Review of Lesson 4
-
Upload
yong-yao-tan -
Category
Education
-
view
802 -
download
2
description
Transcript of CM4106 Review of Lesson 4
![Page 1: CM4106 Review of Lesson 4](https://reader035.fdocuments.us/reader035/viewer/2022062614/546a6af2af7959973b8b5f7a/html5/thumbnails/1.jpg)
CM4106 Chemical Equilibria & Thermodynamics
Lesson 4Solubility Equilibria
A Chemistry Education Blog by Mr Tanhttp://chemistry-mr-tan-yong-yao.blogspot.sg/
![Page 2: CM4106 Review of Lesson 4](https://reader035.fdocuments.us/reader035/viewer/2022062614/546a6af2af7959973b8b5f7a/html5/thumbnails/2.jpg)
Solubility of Common Salts
Courtesy of Chemistry, 10th Edition by Raymond Chang
![Page 3: CM4106 Review of Lesson 4](https://reader035.fdocuments.us/reader035/viewer/2022062614/546a6af2af7959973b8b5f7a/html5/thumbnails/3.jpg)
Fundamentals:
AxBy (s) ⇌ xAy+(aq) + yBx(aq)
• The equilibrium constant for this heterogeneous equilibrium is called the solubility product, Ksp, is written as:
Ksp = [Ay+(aq)]x
eqm [Bx-(aq)]y
eqm
• The solubility product, Ksp, of a sparingly soluble salt is defined as the product of the concentration of the ions (in M) in a saturated solution at a given temperature raised to the power of its coefficient in the equilibrium equation.
Page 69
![Page 4: CM4106 Review of Lesson 4](https://reader035.fdocuments.us/reader035/viewer/2022062614/546a6af2af7959973b8b5f7a/html5/thumbnails/4.jpg)
• The solubility of AgCl at 18°C is 1.46 x 10-3 g/L, what is the solubility product of AgCl at 18°C?
Since the solubility of AgCl = 1.46 x 10-3 g / L; [Ag+] = (1.46 x 10-3 g/L) / (143.5 g/mol)
= 1.017 x 10-5 mol/L
Calculating Ksp value from solubility
AgCl (s) ⇌ Ag+ (aq) + Cl (aq) Initial / M - 0 0
Change / M - s + s + s
Eqm / M - s s
Ksp = [Ag+] [Cl] = (1.017 x 10-5)2
= 1.03 x 10-10
The solubility product of AgCl at 18°C is 1.03 x 10-10
![Page 5: CM4106 Review of Lesson 4](https://reader035.fdocuments.us/reader035/viewer/2022062614/546a6af2af7959973b8b5f7a/html5/thumbnails/5.jpg)
• The Ksp for Ag2CO3 is 8.0 x 10-12 M3, calculate its solubility at this temperature.
Calculating Solubility from Ksp
Ag2CO3(s) ⇌ 2Ag+(aq) + CO32(aq)
Initial / M - 0 0
Change / M - s + 2 s + s
Eqm / M - 2 s s
Ksp = [Ag+]2[CO32]
8.0 x 10-12 = [2s]2[s]8.0 x 10-12 = 4 s3
s = 1.26 x 10-4 M= 1.3 x 10-4 M (2 s.f.)
Solubility of Ag2CO3 = 1.3 x 10-4 M
Let s be the solubility of Ag2CO3 in mol / L
![Page 6: CM4106 Review of Lesson 4](https://reader035.fdocuments.us/reader035/viewer/2022062614/546a6af2af7959973b8b5f7a/html5/thumbnails/6.jpg)
Calculate solubility given Ksp
Calculate Ksp given solubility
Quantitative Problems
![Page 7: CM4106 Review of Lesson 4](https://reader035.fdocuments.us/reader035/viewer/2022062614/546a6af2af7959973b8b5f7a/html5/thumbnails/7.jpg)
Relationship between Ksp and Solubility (M)
![Page 8: CM4106 Review of Lesson 4](https://reader035.fdocuments.us/reader035/viewer/2022062614/546a6af2af7959973b8b5f7a/html5/thumbnails/8.jpg)
Predicting Precipitation - Will a PPT form?Knowing the value of Ksp allows us to predict if a ppt will be
formed when two solutions containing ions to form an insoluble salt are mixed.
Step 1: Calculate reaction quotient Qsp
Step 2: Compare Qsp with Ksp
Inference
Q > K Precipitation occurs till Q = Ksp
Q < K No precipitation is seen because the solution is not saturated with the ions hence they remain dissolved in the solution
Q = K A saturated solution is obtained
Page 75
![Page 9: CM4106 Review of Lesson 4](https://reader035.fdocuments.us/reader035/viewer/2022062614/546a6af2af7959973b8b5f7a/html5/thumbnails/9.jpg)
Predicting Precipitation (Ksp vs Q)Will a precipitate form when 0.10 L of 8.0 x 10-3 M Pb(NO3)2 is added to 0.40 L of 5.0 x 10-3 M Na2SO4? (Ksp = 6.3 x 10-7)
PbSO4 (s) ⇌ Pb2+ (aq) + SO42-
(aq)
Q = [Pb2+][SO42-]
= (0.0016) (0.0040)
= 6.4 x 10-6 > Ksp = 6.3 x 10-7
Q > Ksp ppt will form
REMEMBER: TAKE INTO ACCOUNT OF CONCENTRATION OF IONS IN MIXTURE (DILUTION UPON MIXING)
[Pb2+] = (0.10/0.50) x 8.0 x 10-3
= 0.0016 M [SO4
2-] = (0.40/0.50) x 5.0 x 10-3
= 0.0040 M
![Page 10: CM4106 Review of Lesson 4](https://reader035.fdocuments.us/reader035/viewer/2022062614/546a6af2af7959973b8b5f7a/html5/thumbnails/10.jpg)
Factors affecting solubility
1.Common Ion Effect
2.pH of solution
3.Formation of Complexes
![Page 11: CM4106 Review of Lesson 4](https://reader035.fdocuments.us/reader035/viewer/2022062614/546a6af2af7959973b8b5f7a/html5/thumbnails/11.jpg)
1. Common Ion Effect
Solubility of a substance is affected by the presence of other solutes, especially if there is a common ion present
CaF2 (s) ⇌ Ca2+ (aq) + 2F-
(aq)What happens to the solubility of CaF2 if the solution already contains Ca2+ (aq) or F- (aq)?
1. Equilibrium position shifts to the left2. Solubility of CaF2 decreases
![Page 12: CM4106 Review of Lesson 4](https://reader035.fdocuments.us/reader035/viewer/2022062614/546a6af2af7959973b8b5f7a/html5/thumbnails/12.jpg)
Ksp = [Ca2+][F-]2 = (0.010 + s)(2s)2
Since s is small, assume 0.010 + s ≈ 0.010
(CaF2 is a sparingly soluble salt and the solubility is further
suppressed by the presence of common ion effect)
3.9 x 10-11 = (0.010)(2s)2
s = solubility = 3.1 x 10-5 mol/L
1. Common Ion EffectCalculate the molar solubility of CaF2 at 25 oC in 0.010 M Ca(NO3)2 solution
CaF2 (s) ⇌ Ca2+ (aq) + 2F-
(aq)Initial / M - 0.010 0
Change / M - +s + 2s
Eqm / M - 0.010 + s 2s
Assumption is valid, s << 0.010
![Page 13: CM4106 Review of Lesson 4](https://reader035.fdocuments.us/reader035/viewer/2022062614/546a6af2af7959973b8b5f7a/html5/thumbnails/13.jpg)
2. pH of Solution
If a substance has a basic anion, it will be more soluble in an acidic solution.
If a substance has an acidic cation, it will be more soluble in an basic solution.
![Page 14: CM4106 Review of Lesson 4](https://reader035.fdocuments.us/reader035/viewer/2022062614/546a6af2af7959973b8b5f7a/html5/thumbnails/14.jpg)
2. pH of Solution
Calculate the molar solubility of Mg(OH)2 in pure water. What is the pH of the resulting solution?
Mg(OH)2 (s) ⇌ Mg2+ (aq) + 2OH- (aq)
Ksp = [Mg2+][OH-]2
= (x)(2x)2
1.8 x 10-11 = 4x3
x = Solubility = 1.651 x 10-4 mol/L = 1.7 x10-4 M (2 s.f.)
[OH-] = 2x = 3.302 x 10-4 M pOH = - lg(3.302 10-4) = 3.48 pH = 10.5 (1 d.p.)
Ksp = 1.8 x 10-11 (25 oC)
Initial / M - 0 0
Change / M - +x +2x
Eqm / M - x 2x
Mg(OH)2 (s) ⇌ Mg2+ (aq) + 2OH- (aq)
Page 72
![Page 15: CM4106 Review of Lesson 4](https://reader035.fdocuments.us/reader035/viewer/2022062614/546a6af2af7959973b8b5f7a/html5/thumbnails/15.jpg)
2. pH of Solution What is the solubility of Mg(OH)2 in a less alkaline solution buffered at pH 9?
pOH = 5[OH-] = 1.0 x 10-5 M
Ksp = [Mg2+] [OH-]2
= [Mg2+](1.0 x 10-5)2
[Mg2+] = 0.18 M (2 s.f.)
Page 73
Initial / M - 0 1.0 x 10-
5
Change / M - +x -
Eqm / M - x 1.0 x 10-
5
Mg(OH)2 (s) ⇌ Mg2+ (aq) + 2OH- (aq)
Ksp = 1.8 x 10-11 (25 oC)
![Page 16: CM4106 Review of Lesson 4](https://reader035.fdocuments.us/reader035/viewer/2022062614/546a6af2af7959973b8b5f7a/html5/thumbnails/16.jpg)
With the addition of
acid
![Page 17: CM4106 Review of Lesson 4](https://reader035.fdocuments.us/reader035/viewer/2022062614/546a6af2af7959973b8b5f7a/html5/thumbnails/17.jpg)
3. Complexation
When aqueous ammonia is added dropwise to a Cu2+ solution, a light blue precipitate is observed. As aqueous ammonia is added in excess, the precipitate dissolves to give a deep blue solution.
Page 74
![Page 18: CM4106 Review of Lesson 4](https://reader035.fdocuments.us/reader035/viewer/2022062614/546a6af2af7959973b8b5f7a/html5/thumbnails/18.jpg)
3. Complexation1. When aqueous ammonia is added dropwise to a Cu2+ solution, a light blue precipitate is
observed. As aqueous ammonia is added in excess, the precipitate dissolves to give a deep blue solution.
NH3(aq) + H2O(l) NH⇌ 4+(aq) + OH (aq)
When added to Cu2+(aq) solution, Cu2+(aq) + 2OH (aq) Cu(OH)⇌ 2(s) – (1)Hence a blue precipitate is observed. As more NH3(aq) is added, Cu2+(aq) + 4NH3(aq) Cu(NH⇌ 3)4
2+(aq) [Cu2+] drops as Cu(NH3)4
2+(aq) is formed, thus position of equilibrium in equation 1 shifts left to produce more Cu2+(aq), hence Cu(OH)2(s) dissolves.
Page 74
[Cu(H2O)6]2+ + 2 OH- (aq) → [Cu(H2O)4(OH)2] (s)
[Cu(H2O)6]2+ + 4 NH3 (aq) → [Cu(NH3)4(H2O)2]2+ (aq)
![Page 19: CM4106 Review of Lesson 4](https://reader035.fdocuments.us/reader035/viewer/2022062614/546a6af2af7959973b8b5f7a/html5/thumbnails/19.jpg)
Ksp values