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Introduction to Chem II. Instructors Course Objectives Course Topics Laboratory Exercises Course Website Today’s Agenda Syllabus. Course Objectives. Review some familiar topics Investigate some of these topics at a more in-depth level Model sound pedagogy

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introduction to chem ii
Introduction to Chem II
  • Instructors
  • Course Objectives
  • Course Topics
  • Laboratory Exercises
  • Course Website
  • Today’s Agenda
  • Syllabus
course objectives
Course Objectives
  • Review some familiar topics
  • Investigate some of these topics at a more in-depth level
  • Model sound pedagogy
  • Obtain hand-on practice with Venier Data Collection
  • Show some effective demonstrations
course topics
Course Topics
  • Stoichiometry
  • Calorimetry
  • Equilibrium
  • Solubility
  • Acid-base chemistry
  • Redox chemistry
  • Thermochemistry
5 lab exercises
5 Lab Exercises
  • A calorimetry experiment using a temperature probe
  • Solubility using a Ca ion selective electrode
  • Equilibrium constant using a Colorimeter
  • Acid-base titration
  • Ag Ion Indicator electrode
course website
Course website

http://alpha.chem.umb.edu/chemistry/bpschemII/

Syllabus

Lab experiments

Course notes

Homework solutions

today s agenda
Today’s Agenda
  • Take a 2 hr exam
  • Paperwork, surveys
  • Lunch
  • Lecture; g/mol, Classification of reactions, Stoichiometry, LR, Energetics of Reactions
  • Lab Lecture; Calorimetry
  • Lab Experiment 1
  • Early start on HW
heat of reaction d h
Heat of Reaction - DH
  • At constant pressure – most lab experiments
  • aA + bB → products DH/mol A
  • . DH = q (heat produced or absorbed)
calorimetry
Calorimetry
  • Method of measuring the heat of reaction
  • Calorimeter-coffee cup
  • q = cmDT
    • c is the specific heat [J/(g ºC)] of solution
    • m = mass of solution
    • .DT is change in temperature
  • .DT is directly proportional to the heat of reaction
the experiment
The experiment
  • Mix reactants in different molar ratios
  • Predict the stoichiometry of the reaction from the ratio that gives the maximum temperature increase
example of the experiment
Example of the Experiment
  • 1 to 1, A + B → products
  • Mixing molar ratios
  • Constant total volume - cmDT
example 2
Example 2
  • 2 to 1, 2A + B → products
example 3
Example 3
  • 3 to 1, 3A + B → products
determining the d h m
Determining the DHm
  • . DH = cmDT = (4.4 J/gC)*(50 g)*(36)

= 7920 J

  • mol A reacted = 18.8 mmol A
  • .DHm = DH/(mol A reacted)

= (7920)/(.0188 mol) = 421276 J/mol

= 421 kJ/mol

products
Products
  • Thiosulfate is a classic reducing agent
  • 2S2O32-↔ S4O62- + 2e-
  • Cl- is the product of the reduction of OCl-
  • Write a balanced redox equation
    • Step 1: determine half reactions.
    • Step 2 Make the reduction half reaction and oxidation half reaction have the same number of electrons by multiply reactions by common denominator
    • Step 3: Add reactions
slide19
OCl- + H2O + 2 e- ↔ Cl- + 2OH-
  • 2S2O32-↔ S4O62-+ 2e-
  • ________________________
  • OCl- + H2O + 2S2O32-→ Cl- + 2OH- + S4O62-
goals
Goals
  • Determine the solubility of CaSO4 in three different solution
    • Saturated CaSO4 in H2O
    • Saturated CaSO4 in 0.10 M KNO3
    • Saturated CaSO4 in 0.10 M Na2SO4
  • Compare and rationalize the results
major concepts
Major concepts
  • Solubility Product Constants and saturated solution
  • LeChatlier’s principle and the common ion effect
  • Effect of ionic strength and ion activities on Ksp
  • Ion Selective Electrodes
ksp of caso 4
Ksp of CaSO4
  • CaSO4(s)↔ Ca2+ + SO42-
  • Ksp(CaSO4) = [Ca2+][SO42-] = 2.4∙10-5
saturated solution in water
Saturated solution in water
  • Add several grams of CaSO4 to 1 L of water
  • Shake and mix for weeks
  • Allow CaSO4 that did not dissociate to settle to bottom
  • Ksp(CaSO4) = [Ca2+][SO42-] = 2.4∙10-5

= x2

[Ca2+] = 5.0∙10-3 M

saturated solution in 0 10 m na 2 so 4
Saturated solution in 0.10 M Na2SO4
  • Add several grams of CaSO4 to 1 L of 0.10 M Na2SO4
  • Common Ion effect
  • Ksp(CaSO4) = [Ca2+][SO42-] = 2.4∙10-5

= x(x+0.10)

Assume x <<< 0.10 x = 2.4∙10-4 M

[Ca2+] = 2.4∙10-4 M

saturated solution in 0 10 m kno 3
Saturated solution in 0.10 M KNO3
  • Activities
  • Ksp(CaSO4) = ACa2+ASO42- = [Ca2+]gCa2+[SO42-]gSO42- = 2.4∙10-5
  • Activity coefficient (g) is dependent on the ionic strength of the solution, and the size and charge of the ion. It is a number between 0 and 1. At very low ionic strength, g approaches 1
ionic strength
Ionic strength
  • A measure of the concentration of ions in solution

m = ½ ∑ cizi2

Sat. solution in 0.10 M KNO3

m = ½ ([K+](+1)2 + [NO3-](-1)2 + [Ca2+](2+)2 + [SO42-](-2)2) = 0.12 M

gCa2+@m=0.12 =

take home message
Take home message
  • The common ion effect decreases the solubility by over an order of magnitude
  • At high ionic strengths, solubility increases slightly ( by a factor of 1.5 -5).
ion selective electrode
Ion Selective Electrode
  • A probe that consists of two reference electrodes connected electrically through a specific type of salt bridge through the solution being measured.
  • The salt bridge is a membrane that specifically binds the ion of interest
  • A junction potential develops at this membrane that is proportional to the concentration of the ion of interest
slide30

voltmeter

Cathode

Reference electrode

Ag/AgCl, sat. KCl

Anode

Reference electrode

Ag/AgCl, sat. KCl

solution

Ion selective

membrane

Engineer this whole set-up in one probe

pH meter

Ca2+ selective electrode

response of ca 2 selective electrode
Response of Ca2+ Selective Electrode
  • Ecell = constant + 29.58 logACa2+