Percent Copper in Brass

Product Details

The relative proportions of copper, zinc and iron in brass influence its properties and uses. How can the percent composition of brass be determined to verify these properties?

The purpose of this advanced-inquiry lab is to design a procedure to analyze the amount of copper in brass using visible spectroscopy. The lab begins with an introductory activity in which students measure the absorbance of various metal ion solutions at regular wavelength intervals from 400 nm to 700 nm and investigate the influence of the anion on the absorption spectra. Students identify the correlation among wavelength, absorbance and concentration for each of three possible ions that may be obtained from brass: copper, zinc and iron.

Then students design and carry out an experiment to construct a calibration curve and determine the concentration of copper ions in a solution prepared by dissolving brass in nitric acid. Students must investigate the concentration range over which Beer’s law is valid and identify the optimum wavelength for analysis. The mass percent of copper in brass is determined from the results of the analysis.

Complete for 24 students working in pairs. Perform this experiment in a fume hood or well-ventilated lab. Refill kit includes chemicals and consumable items.

2024 CED Alignment:  

Unit 3 - Properties of Substances and Mixtures  

Topic 3.13 - Beer-Lambert Law 

Description of the Lab  

Students use spectrophotometry to create a calibration curve and determine the copper content in a brass sample. The lab builds mastery of Beer's Law and reinforces quantitative reasoning, precision, and the link between absorbance and concentration. 

Learning Objective 

• LO 3.13.A – Explain the amount of light absorbed by a solution or molecules or ions in relationship to the concentration, path length, and molar absorptivity. 

Skills Students Will Learn 

• 3.A – Represent chemical phenomena using appropriate graphing techniques, including correct scale and units. 
  In this lab: Students graph absorbance vs. concentration to build a calibration curve. 

• 5.F – Calculate, estimate, or predict an unknown quantity from known quantities by selecting and following a logical computational pathway and attending to precision (e.g., performing dimensional analysis and attending to significant figures). 
  In this lab: Students use the calibration curve and Beer's Law to determine concentration. 

• 6.B – Support a claim with evidence from experimental data. 
  In this lab: Students use quantitative results to support their percent composition calculation.