Introduction to Spectroscopy Student‘s Manual Deutscher Akademischer Austauschdienst DAAD German Academic Exchange Service by Katja Streidel Julius-Maximilians-Universität Würzburg Fakultät für Chemie und Pharmazie Würzburg, 2016 Contents Contents 0 Introduction .......................................................................................................................................... 2 0.1 Set-up of the Manual ............................................................................................................... 2 0.2 Set-up of the Laboratory ......................................................................................................... 3 0.3 Safety Instructions ................................................................................................................... 3 1 Day I - Light ........................................................................................................................................... 4 1.1 The Scientific Method ............................................................................................................. 4 1.2 Introduction – Mind Map ........................................................................................................ 5 1.3 Properties of Light ................................................................................................................... 6 1.3.1 Light as a Wave ................................................................................................................ 6 1.3.2 Double Slit Experiment: ................................................................................................... 9 1.4 Properties of White Light ...................................................................................................... 13 1.5 Conclusion ............................................................................................................................. 16 2 Day II – The Different Parts of a Spectrometer .................................................................................. 18 2.1 Expert Groups ........................................................................................................................ 18 2.2 The Transmission Diffraction Grating .................................................................................... 20 2.3 The Slit ................................................................................................................................... 26 2.4 Light and its Measurement ................................................................................................... 30 2.4.1 Grease Spot Photometer ............................................................................................... 30 1.4.2 The Beer-Lambert Law .................................................................................................. 37 3 Day III – Working with the Spectrometer ........................................................................................... 43 3.1 Assembling the Spectrometer ............................................................................................... 43 3.2 Calibration ............................................................................................................................. 44 3.3 Experiments and Measurements .......................................................................................... 49 3.3.1 Measuring the Emission Peaks of LEDs ................................................................................ 49 3.3.2 Qualitative Experimental Proof ............................................................................................ 50 3.4 Conclusion ............................................................................................................................. 53 4 Glossary .............................................................................................................................................. 55 5 List of Figures ...................................................................................................................................... 57 6 Bibliography ........................................................................................................................................ 59 1 Introduction 0 Introduction Welcome to the manual “Introduction to Spectroscopy”. This manual will guide you through the next three days of laboratory work, where you will learn about how a spectrometer works. The manual provided will help to guide you through the procedure if you follow along closely. However, remember that your assistants are always there to help you out when you get stuck or have questions. Please listen to your assistants safety instructions and try to follow the instructions of the manual as precisely as possible in order to ensure a safe working environment and the best results. I hope you enjoy the laboratory! 0.1 Set-up of the Manual The set-up of the manual follows the structure of the manual “An Introduction to Drinking Water Analysis” [1] in order to save you the time of having to adopt to a different structure. Because the lab is designed to be conducted over three days the manual is divided into three main chapters, completed with a glossary, list of figures and bibliography. The boxes you will find throughout the manual are designed to help you orientate yourself more quickly and notice the important aspects of a topic: • Yellow highlighting: This highlighting means that you are not allowed to go on without getting important instructions from your assistant. • Bold, blue writing: This code means that the word is a keyword with an important definition that can be found in the glossary at the end of the manual. • Orange box: learning expectations In this box you will find what you are supposed to learn in the course of the next unit. Please read these learning expectations carefully before starting with the unit! • Blue box: task box In this box you will find the tasks you need to complete throughout the next unit. Solutions for study questions will be provided in the solutions section at the end of each day. • Clock symbol: working time The clock tells you the time that you will need in order to complete the unit. Once your group is done please do not disturb the other groups. Either wait for the next task or continue on with the manual. 5 min 2 Introduction 0.2 Set-up of the Laboratory The laboratory is designed to be worked through in 3 days with 3 hours each. Figure 1 below provides an overview of the topics covered by the lab and what will happen during the respective days. Schedule of the laboratory: Figure 1: Lab schedule. 0.3 Safety Instructions Please, make sure you must always wear a lab coat and safety goggles during your stay in the laboratory in order to ensure the best protection of your eyes and skin. Also be mindful of others and try to work as responsibly and courteously as possible to not risk harming yourself or others. Any amount of chemicals could potentially endanger you or your environment, so proceed with the necessary caution and do not hesitate to ask your assistant when you are unsure about an experiment. 3 Day 1 - Light 1 Day I - Light 1.1 The Scientific Method As scientists examine and gather information about the world, they follow a typical process called the scientific method. It begins with an observation or question that the scientist will then investigate. Next, the scientist typically performs some research about the topic and then constructs a hypothesis. After that, the hypothesis will be tested by performing an experiment. Finally, the scientist analyzes the results of the experiment and draws a conclusion. Note that this often leads back to another question, which is why the scientific method is often considered a circle as illustrated in Figure 2. [2] Figure 2: The scientific method depicted in a circle. In the following workshop you are now asked to apply the scientific method. The manual as well as your assistants will guide you through the process. Do not hesitate to ask for help when needed. 4 Day 1 - Light 1.2 Introduction – Mind Map Learning expectations: • Activating existing knowledge about light • Expanding knowledge about light • Creating a cooperative learning base on which to build upon • Using the scientific method in order to gain scientific knowledge Create a mind map for the central concept of light 15 min 1 QUESTION: What is light? In the following workshop everybody gathers around a central board and will create a mind map about LIGHT together. Please wait for further instructions from your assistants and then start on the mind map. 5 Day 1 - Light 1.3 Properties of Light Learning expectations: • Understanding the different properties of light (characterization of light) • Understanding the fundamentals of the wave characteristics of light • Conducting individual experiments in groups, while working as a team • Working with the scientific method 2 RESEARCH 1.3.1 Light as a Wave • Read through the theory part of the experiment and explain and discuss the theory together (background research) • Set up the experiment and conduct it as a team • Work according to the scientific method 50 min In this workshop you will look at the different properties of light. This knowledge is important so you can ultimately understand how a spectrometer works, and bring light into the darkness of this previously “black box” like equipment. Visible light, as it is used it in UV/VIS spectrometers, is a form of energy called electromagnetic