Line Spectra of Elements

Students used Bunsen Spectroscopes to measure positions of emission lines from a hydrogen discharge lamp.

The calibration of the spectroscope with a helium lamp, followed by measurement of hydrogen lines, was time-consuming at best. The activity required essentially the entire lab period.

The spectrometer is used to quickly and easily measure hydrogen lines, so the students still go through the exercise of assigning quantum numbers to H-atom transitions, etc,. Much lab time is saved, however, and is spent on the measurement of line spectra from flames.

Students employ the spectrometer to measure emission spectra from a burner flame into which various salts are introduced. The entire group of students on one network first work together to determine he emission spectra for a set of six known solutions (salts of Na, K, Li, Sr, and Ca)  Each pair of students is then given three or four unknown solutions, each of which contains any one, two, or three of the known substances. They measure the flame emission of each unknown and determine the substances present.

The experiment is colorful and impressive. Students enjoy the analytical puzzle of the unknowns.