Chem 2002: Midterm Review

Objective: Measurement of water volumes (10 mL, 20 mL) and their mass.
Tools Used:
- Beakers: Not calibrated; used for holding reactions, intermediate steps, or avoiding reactions over heat.
- Volumetric Glassware: Calibrated for specific temperature (20°C); cannot be heated beyond calibration marks. Includes:
  - Burette: Ideal for titration experiments due to precise liquid dispensing control.
  - Volumetric Pipettes: Dispense specific volumes (1 mL, 2 mL, 5 mL, etc.) without variability.
  - More or Surgical Pipettes: Variable volumes, handy for different requirements.
  - Micropipettes: For small volumes, from 10 µL to 5,000 µL (less accurate over 1,000 µL).
  - Graduated Cylinders: Approximate volume measurements, less precise than volumetric glassware.
Statistical Tests Applied: Case 2, Case 3, and F-tests; calibration plot referenced for further experiments.

Scenario: Comparing arsenic detection methods.
Used pooled standard deviation and t-tests.
Found the t-value of 2.785 through calculations and compared with t-table values for significance.
Result indicated that the new method is not reliable for arsenic detection; original method preferred.

Method: Titration analysis for calcium ions.
Key Steps:
- Standardized sodium hydroxide due to concentration variations over time.
- Used potassium hydrogen phthalate (KHP) as primary standard, which doesn’t degrade.
- Calculated moles of leftover HCl to determine moles in antacid tablets.
- Used indicators for endpoint determination during titration.
Results: Percent mass of calcium in the tablets calculated based on titration results.

Parts:
1. Identifying functional groups in pure molecules (pentanol, toluene, methyl ethyl ketone).
2. Quantitative analysis using Beer's Law.
Beer's Law: Absorbance = ε × b × c; maintaining constant path length for accurate concentration results.
Example: Calculated absorbance of CH peak in hexane using tangent baseline method.

Methods Used:
- Calibration Plot Method: Standards with only zinc solutions.
- Standard Addition Graphical Method: Samples contained vitamin water with varying zinc concentrations.
Discussed matrix effects and importance of keeping conditions consistent for accurate results.
Compared methods and highlighted that standard addition minimized matrix errors better than the calibration plot method.

Analyzed absorbance data from both methods to determine zinc concentrations, accounting for dilutions.
Dilution Equation: Used to track concentrations through calculated absorbance in solutions.

Familiarize with lab techniques and calculations from each experiment.
Bring necessary tools (calculator, pen, ruler) for all calculations during the exam.
Review the recording of the session for details on difficult concepts.
Be prepared to apply statistical tests discussed for evaluation of results.