1. CHE118 Introduction 1CHE118

2. Topics Syllabus, experiment schedule, student drawers, CHE118 packet Safety items and contract Calibration scales Calibration Curve and Spectrophotometer 2CHE118

3. Safety Concerns Additional safety concerns that were not mentioned on the safety contract will be discussed using another PowerPoint file. 3CHE118

4. Calibration Scales Know how to read the calibration marks on a piece of calibrated glassware and determine: 1.the correct number of significant figures 2.the correct volume reading BCC YouTube video 4CHE118

5. Graduated Cylinder 10 mL and 100 mL sizes are most common 0.0 mL when empty, 10.00 mL when full (or 100.0 mL when full) In General: 1.Find difference between numbered tick marks 2.Use the un-numbered tick marks between the two numbered marks, count the number of jumps from one numbered mark to the other 3.Determine what each un-numbered mark is worth 4.Estimate one digit beyond the un-numbered tick marks (this is the last significant digit for the volume) 5.Read the volume, using the correct number of significant figures 5CHE118

6. Graduated Cylinder (in student drawer) 6CHE118

7. SF and Volume Reading Difference between numbered calibration tick marks: 8 mL – 7 mL = 1 mL There are 9 un-numbered tick marks between the 7 and 8 marks (10 jumps from 7 to 8) Each un-numbered tick mark is worth: 1 mL / 10 jumps = 0.1 mL per jump Estimate one digit beyond un- numbered mark 0.1? mL (use 2 digits after decimal point for SF,. _ _ mL) 7CHE118

8. Read a Volume with Correct SF 10 mL graduated cylinder Read volume at the bottom of meniscus, at eye level More than 7, less than 8 7.? ? mL 7.5 ? mL 7.53 mL 8CHE118

9. Calibration Curve and Spectrophotometer Work in groups of four. Everyone must make their own calibration curve. CHE1189

10. Calibration Curves Calibration curves show the linear relationship between absorbance and concentration. CHE11810 Absorbance Concentration, M

11. Spectrophotometer An instrument that will indicate the amount of light (of one wavelength) absorbed by a sample CHE11811 LED readout readout detector sample monochromator Light source slit

12. Beer – Lambert Law A = abc A is absorbance of light by the sample a is the molar extinction coefficient b is the solution path length c is the concentration of solute This is a linear relationship; y = mx + b A = mc + b CHE11812

13. Making the Calibration Curve You will acquire an absorbance reading for each standard solution provided Plot the corresponding concentration and absorbance values as data points on a graph to construct the calibration curve CHE11813

14. Calibration Curve CHE11814 Absorbance Concentration, units absorbance reading concentration Data point

15. Find the Absorbance of the Unknown Solution 1.Use a disposable transfer pipet (plastic) to almost fill a small test tube with the unknown solution 2.Wipe the outside of the test tube (remove droplets and fingerprints) 3.Place this test tube in the sample compartment of the spectrophotometer (use the same spectrophotometer each time) 4.Record the absorbance readout from the spectrophotometer CHE11815

16. Find the Concentration of the Unknown Solution 1.You will have an absorbance reading for your solution (from the spectrophotometer). 2.Find that absorbance reading on the y axis of the calibration curve. 3.At that point on the y axis, move horizontally across to the calibration curve line (use a ruler) 4.When you reach the line, drop straight down to the x axis 5.The value that you are at on the x axis is the concentration of your solution CHE11816

17. Using the Calibration Curve to Find Concentration of the Unknown Solution CHE11817 Absorbance Concentration, units Unknown solution absorbance reading Concentration of unknown solution