Podcast
Questions and Answers
What is the relationship between absorbance and transmittance?
What is the relationship between absorbance and transmittance?
Why can't different Nessler's tubes be used for optical density measurements?
Why can't different Nessler's tubes be used for optical density measurements?
What forms when ammonia is added to copper sulfate in the analysis?
What forms when ammonia is added to copper sulfate in the analysis?
What is the purpose of a blank solution in optical density measurements?
What is the purpose of a blank solution in optical density measurements?
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At what wavelength is maximum absorbance of the cuprammonium sulfate complex observed?
At what wavelength is maximum absorbance of the cuprammonium sulfate complex observed?
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What conditions must be met for satisfactory colorimetric analysis?
What conditions must be met for satisfactory colorimetric analysis?
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Which statement accurately describes the graph of absorbance versus concentration?
Which statement accurately describes the graph of absorbance versus concentration?
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Why is a constant path length crucial in optical density measurements?
Why is a constant path length crucial in optical density measurements?
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Study Notes
Engineering Chemistry Lab Manual
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Absorbance/Optical Density: The reciprocal of transmittance (log (1/T)).
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Nessler's Tubes (Cuvets): Cannot be used interchangeably for optical density measurements because optical density depends on the path length within the tube.
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Solution Volumes in Flasks: Different volumes are used to create standard solutions of varying concentrations for calibration curves.
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Ammonia Addition: Ammonia is added to form a cuprammonium sulfate complex ([Cu(NH3)4]SO4), a dark blue complex, to nullify absorbance from impurities in ammonia.
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Copper Determination: CuSO4 + 4 NH4OH → [Cu(NH3)4]2+ + SO42- + 4 H2O (Tetraaminecopper(II) - Dark blue).
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Blank Solution: Identical to the test solution, except for the metal ion of interest.
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Wavelength for Copper Estimation: 620 nm, as this wavelength shows the maximum absorbance of the cuprammonium sulfate complex.
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Constant Path Length: Essential for determining the concentration of an unknown solution through comparison with known solutions, enabling accurate concentration estimation.
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Blank Solution as Reference: A blank solution is used as the reference to zero, enabling accurate optical density measurements.
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Origin on Graph: The graph of absorbance vs. concentration passes through the origin because the absorbance of the blank solution is zero, making it the reference point.
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Satisfactory Colorimetric Analysis:
- Solutions must adhere to Beer-Lambert's Law, avoiding salvation, association, dissociation, or hydrolysis.
- Colors of the solutions must remain stable during the analysis.
- Solutions should be clear and free of precipitates.
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Description
This quiz covers essential concepts from the Engineering Chemistry Lab Manual, including optical density measurements, solution preparation, and copper determination techniques. Understand the importance of cuvettes, calibration, and blank solutions in analytical chemistry. Test your knowledge of these crucial laboratory procedures.
