Spec20

Purpose

To find an unknown concentration of a solution by plotting known concentration of the same solution vs absorbance. A handout for the students is available here: File:Maxie - Spec20 Station Handout.docx.

Experiment

0. Preparation: Make sure the spectrometer wavelength is set to 590 nm. The instructions to calibrate the spectrometer is labeled on the front of each Spec20. Prepare six test tubes with percents ranging from 0% to 100% of blue dyes. Test tube 1 is water only it is to be used as the blank. Also every student should have one test tube labeled unknown.

1. Ask the students to draw two columns on a sheet of paper with PERCENT on top of column one and DATA on top of column two.

2. Ask the students to put test tube number 1(BLANK) into spec20. Check each station to make sure the absorbance reading is approximately is zero.

3. Ask the students to put test tube from number 2 to number 5 while reading off the reading corresponding percents 20%, 50%, 80% and 100% and tell them to record it in the PERCENT column as well as record the absorbance in the DATA column.

4. Ask the students to put the last test tube labeled "ev"(UNKNOWN) into the Spec20. Write down the absorbance reading in the data column and mark it as "x" in the percent column.

5. Inform the students to take the data sheets to the computer station.