A chem 2-25-25

Midterm Review

• Overall performance was satisfactory.

  • Average score: 70.4.

  • No extra credit questions; attendance today grants 5 points extra.

Homework Reflection

• Homework's effectiveness questioned.

  • Specific example: Question 1c replicated on exam led to poor performance despite strong homework scores.

• Concerns about students using AI tools or online resources rather than understanding the material.

  • Reminder to use resources wisely for learning, not just answers.

Exam Feedback

• Overview of exam performance by question:

  • Question 1: Homework application evident, but low performance on the exam.

  • Question 2: Statistics section performed well, students understood.

  • Question 3: Stoichiometry problem met with mixed success, focus on mole calculations needed.

    • Common mistake noted: calculating moles of oxalate in 25 mL.

  • Question 4: Common ion effect understood and many answered correctly.

  • Confidence interval responses were fair; reminders on answering format emphasized (percentage vs. probability).

  • Last questions on unit conversions were satisfactory.

Upcoming Tasks

• Homework 4 assigned, due next Monday; Quiz 3 scheduled for March 4.

• Review of chapters 6 and 7 upcoming; finishing chapter 6 today.

Chapter Topics

Solubility Products

• Definition: Product of the concentration of constituent ions forming a precipitate.

• Precipitation titrations focus on curves showing how ion concentrations change with titrant addition.

Titration Curves

• Titration Curve Definition: Shows reactant concentration variation as titrant is added.

  • Importance of recognizing equivalence point visually and through indicators.

  • Conversion from theoretical (stoichiometric) to practical (visible endpoint).

• Endpoint Indicators: Use of organic dyes; their relationship with ion concentrations affects visibility.

• Precipitation reactions prioritize product-favored equilibrium conditions.

Case Study: Titration of Ag+ and I-

• Analysis of reactions in precipitation: Ag+ reacts with I- to form silver iodide.

  • Key calculations include relating moles to volume and concentration.

  • Understanding Ksp's role in predicting precipitate behavior and solubility limits.

Analysis of Titration Curves

• Different solubility insights from steepness of curves.

  • Interpretations: P-T curves predict order of solubility for salts (iodides > bromides > chlorides).

Gravimetric Analysis (Introduction to Chapter 7)

• Gravimetry: Accurate mass measurement for substance quantification.

  • Considerations on processes making gravimetric analysis tedious but essential for accuracy.

  • Roledirect vs. indirect measurements using combustion analysis.

• Overview of Procedure: Precipitation and post-treatment are critical for obtaining valid results.

• Example with Iron Analysis: Precipitation of Fe(OH)3; the purification process to arrive at Fe2O3 for accurate mass measurement.

Criteria for Successful Gravimetric Analysis

• Ideal product characteristics:

  • Purity and insolubility.

  • Large particle size for easy filtration.

  • Known composition for stoichiometric calculations.

Mechanisms of Precipitation

• Two processes:

  • Nucleation: Initial particle formation.

  • Particle Growth: Formation of stable aggregates.

Relative Supersaturation Concept

• Defines conditions favoring nucleation vs. growth rates.

  • Techniques to control RSS for optimal outcomes:

  • Increase solubility through temperature elevation.

  • Careful titrant application.

  • Dilution with larger volumes to decrease concentration.

Wrap-Up

• Verification of understanding through practical problem sets.

• Importance of foundational knowledge for future studies in analytical and inorganic chemistry.