Engineering Chemistry Lab Manual Overview

Engineering Chemistry Lab Manual

• Absorbance/Optical Density: The reciprocal of transmittance (log (1/T)).

• Nessler's Tubes (Cuvets): Cannot be used interchangeably for optical density measurements because optical density depends on the path length within the tube.

• Solution Volumes in Flasks: Different volumes are used to create standard solutions of varying concentrations for calibration curves.

• 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.

• Copper Determination: CuSO₄ + 4 NH₄OH → [Cu(NH₃)₄]²⁺ + SO₄^2- + 4 H₂O (Tetraaminecopper(II) - Dark blue).

• Blank Solution: Identical to the test solution, except for the metal ion of interest.

• Wavelength for Copper Estimation: 620 nm, as this wavelength shows the maximum absorbance of the cuprammonium sulfate complex.

• Constant Path Length: Essential for determining the concentration of an unknown solution through comparison with known solutions, enabling accurate concentration estimation.

• Blank Solution as Reference: A blank solution is used as the reference to zero, enabling accurate optical density measurements.

• 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.

• 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.