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Percent Copper in Brass AP Inquiry Lab

Percent Copper in Brass AP Inquiry Lab. Brass is an alloy of copper and zinc. It may contain small amounts of iron, lead, aluminum and tin. The amount of copper in brass affects its color, hardness, ductility, mechanical strength, electrical conductivity, etc…

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Percent Copper in Brass AP Inquiry Lab

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  1. Percent Copper in Brass AP Inquiry Lab

  2. Brass is an alloy of copper and zinc

  3. It may contain small amounts of iron, lead, aluminum and tin. • The amount of copper in brass affects its color, hardness, ductility, mechanical strength, electrical conductivity, etc… • Spectroscopy provides a tool for determining the percent copper in brass.

  4. Transition metals have partially filled d-orbitals. • The presence of water molecules (or other ligands) surrounding a transition metal ion in solution leads to energy differences among the d-orbitals • Depending on the metal involved, the energy difference may correspond to different wavelengths and energies of visible light

  5. This property of transition metal ions gives many their characteristic colors

  6. The concentration of a colored transition metal ion solution can be determined by measure the color intensity using a spectrophotometer.

  7. Beer’s Law Review • In general, absorbance is proportional to concentration • Higher concentration= more intense color= greater absorbance of light • The amount of light absorbed by a solution depends on its concentration (c) as well as the path length (b) of the sample cell. A = Ebc • Where E (epsilon) is a constant known as the molar absorptivity coefficient, which is dependent on the nature of the absorbing solution system and the wavelength of the light passing through it.

  8. Quick Overview of calculations: • You will use the spectrophotometer to get a value for “T” (transmittance). If you need to change that to %T, multiply T by 100. • Use T to solve for A (A= -logT) • Using your calculated value for A and the molar absorptivity coefficient for the wavelength of light used, you can then use Beer’s law to solve for concentration (A= Ebc)

  9. In plotting Absorbance vs. Concentration The concentration of the unknown can be determined by finding its absorbance and plugging it into the equation for the best fit line of y=mx + b • y= mx + b • Where • y= Absorbance(which is –log T) • m= slope • x= concentration(need to solve for this!) • b= y-intercept, which should be zero. A = m[concentration] + 0

  10. See PDF attached for instructions for your lab notebook!

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