- Количество слайдов: 24
Gen. Chem Week 4 Chemical Synthesis Week one of a two-week experiment Today’s Agenda: Introduction to chemical syntheses Determining reaction yield Issues associated with the synthesis Synthesize aspirin Recrystallize the aspirin.
Gen. Chemical Synthesis: What is it? From Wikipedia, the free encyclopedia In chemistry, chemical synthesis is the purposeful execution of chemical reactions in order to get a product, or several products. Can you rewrite this definition to make it better?
Gen. Chem Intro to Measurement Computer-Graded Pre-lab assignment
Let′s think! Gen. Chemical Synthesis: Examples In your groups, make a list of some things in your life that are the result of chemical synthesis. Medicines Plastics A wide array of things we use every day.
The Problem Imagine that you work for a firm that has been hired to make house-brand aspirin for a large national chain. The managers have decided to use the reaction of salicylic acid with acetic anhydride in the presence of an acid catalyst to make acetylsalicylic acid (aspirin) and acetic acid. Your group is assigned the task of determining the conditions that produce the highest yield of aspirin. Gen. Chem
Gen. Chem Let′s think! Making Aspirin In your groups complete the following microscopic representation of this reaction with five of each reactant. Symbol Key Acid catalyst Salicylic acid H Acetic Anhydride Acetyl salicylic acid Acetic Acid H H H
Gen. Chem Let′s think! Complete this microscopic representation having five salicylic acids and eight acetic anhydrides. Symbol Key Acid catalyst Salicylic acid H Acetic Anhydride Acetyl salicylic acid Acetic Acid H H H What is the ‘limiting reagent”? H
Gen. Chem Let′s think! Limiting Reagent For the reaction you will be performing today. Acid catalyst Given 2 grams of salicylic acid and 5 m. L of acetic anhydride (density = 1. 08 g/m. L) which is the limiting reagent?
Gen. Chem Let′s think! Consider another issue. What if all the salicylic acid does not react? Symbol Key Acid Complete the microscopic representation. catalyst Salicylic acid Acetic Anhydride What is the “yield”? Acetyl salicylic acid What is the “percent yield”? Acetic Acid H reaction H H H loss H H H
Gen. Chem Material Safety Data Sheets While we’re looking up chemicals, lets also look at the best source of information regarding the dangers of chemicals – the material safety data sheet.
Let′s think! Gen. Chem The Problem You do some research and discover the following: the best catalyst is concentrated phosphoric acid (H 3 PO 4). the reaction does not appreciably occur at room temperature. significant side reactions occur at temperatures of 100 o C and above. the reaction is destroyed by water. Care must be taken to keep water out of the reaction flask. The Problem is to determine the “best” temperature at which to perform the reaction. In your groups, come up with a plan for how you expect to do this.
Gen. Chem Let′s think! Determining Product Yield What will you need to know? What measurements will you need to make? • identity of the “limiting reagent” • mass of limiting reagent • mass of product • molar masses
Let′s think! Making Aspirin In your groups review your responses to the following prelab question and come up with a consensus answer. Using the Summary of Steps given in chapter 11 of the lab book as a guide prepare a set of directions for performing the reaction. Gen. Chem
Tips for the reaction Make sure your procedure accounts for the following. • You are to check out the specialty items you will need for the experiment. • Suspend thermometer in the water bath so that it doesn’t touch the container. • Use a cotton plug to keep water out of the reaction flask. Gen. Chem
Let′s think! Isolating the Aspirin Gen. Chem In your groups review your responses to the following pre-lab question and come up with a consensus answer. Create a procedure for obtaining aspirin crystals from the reaction mixture. Make sure you indicate what materials and equipment you expect to use.
Tips for the isolation Gen. Chem Make sure your procedure accounts for the following. • Recommended procedure for creating an ice bath. Half fill a beaker with ice. Sprinkle rock salt over the ice. Use enough to lightly cover the ice. Add some water until the ice is slushy. • Leave flask in ice bath for about 5 minutes after crystallization appears to be complete. • A spatula is provided to assist with the removal of crystals from the flask. • The crystal product must be washed with a small amount of cold distilled water. Cool some in a beaker in an ice bath. Use an eye dropper or transfer pipet dribble 2 m. L (40 drops) of the cold water over the crystals while still drawing a vacuum on the funnel. • Store the crystals for analysis next week, Store so they are open to the air so they will continue to dry.
Performing the reactions safely. Gen. Chem The reagents used in this reactions have the potential to cause chemical burns and possibly allergic reactions. To protect yourself from inadvertent contact with these chemicals you should wear gloves while performing the experiment.
Gen. Chem Safety precautions the acetic anhydride is destroyed by water. All glassware must be dry. the reaction of acetic anhydride with water can be violent. the amounts of material are small. It would be easy to loose ALL of your aspirin.
Gen. Chem Let′s explore! First Challenge Following the procedure given in your lab manual, manufacture some aspirin. Available resources: v Salicylic acid, acetic anhydride and sulfuric acid. v Balances. v Volumetric glassware. EVERYONE is to perform the synthesis INDIVIDUALLY. You have 60 minutes
Gen. Chem Determine Your Crude Product Yield In your groups review your responses to the following pre-lab question and come up with a consensus answer. Describe how you will go about determining the percent yield of your crude product. Describe the mathematical operations you will have to perform.
Gen. Chem Let′s think! What’s next? Can we put The government will require purification and testing before we can market. our crude aspirin into tablets? What kind of chemical analysis is purification? How are we going to achieve it? • separation • precipitation
Gen. Chem Let′s think! What’s next? Can we put our recrystallized aspirin into tablets? What kind of chemical analysis remains to be done? How are we going to achieve it? • melting point • TLC
Gen. Chem No Report No report is assigned until the third week has been completed. Week Two Pre-lab Assignment The pre-lab assignment for next week will ask you to correctly calculate the percent yield for the crude product and to construct a draft introduction for the experiment