Queensborough Community College 23

Chapter 1: Introduction

Discusses the concept of determining the concentration of an unknown substance.
Each student has different unknown concentrations to work with; examples were given (e.g., Unknown 35 should yield a concentration of 105).
Class engages in calculating percent error based on their results.
The importance of graphing data is emphasized.
- Use of Excel for graphing or plotting the data was mentioned.
- Guidance on adding a trend line and displaying the equation on a graph.

Calibration curve utilized to establish the relationship between concentration and absorption.
Discussed Beer-Lambert Law, which states that absorbance (A) is directly proportional to concentration (C).
The objective of the lab:
- To determine the concentration of an unknown copper sulfate solution using spectrophotometry and Beer-Lambert law.
Key chemical concepts:
- Molarity: Measure of concentration.
- Absorption: The ability of substances to absorb light.
- Wavelength: Key factor in determining absorption properties.

Reiterates important terms:
- Spectrophotometry, Absorption, Molarity, Dilution, Calibration.
Discussed materials required for the experiment:
- 4 x 25 mL Erlenmeyer flasks, 2 x 10 mL beakers.
- The spectrophotometer and computer interface for data collection.
Emphasized that copper sulfate (CuSO4) is used without relying on a chemical reaction but rather on its physical properties.
- Observational color (blue) and understanding of light absorption (absorps red) discussed.

Important physical properties discussed:
- Wavelength, Concentration, Volume.
Mathematical relationship established by Beer-Lambert Law: A = ELC (Absorbance = Molar absorptivity x Path length x Concentration).
Data collected included concentrations of copper sulfate and their corresponding absorption values.
- Result of the experiment would be presented in terms of the final concentration of the unknown.
Explanation of how to derive the unknown concentration from the data and calibration curve results.

Emphasizes the procedure of making a calibration curve using known concentrations and their absorption.
Calibration curve is fundamental for determining the unknown concentration by deriving the equation from the graph.
Final concentration is calculated by plugging the unknown absorption value into the derived equation.
- It’s critical to present the data systematically.
Clear structure is encouraged in writing up results, avoiding first-person language.

Summarization of key findings: Determined the concentration of an unknown copper sulfate solution through calibration and Beer-Lambert law.
Discussed potential sources of error in the experiment:
- Oversights in preparing dilutions (like adding too much water, inaccurate measurements).
- Contamination and incorrect placement in the spectrophotometer affecting readings.
Mention of upcoming exams: ACS exam and the final lab review.
- ACS exam provides an opportunity for extra credit, emphasizing the importance of participation.
Encouragement to focus on proper methodology and understanding of concepts for successful outcomes.