LS2_a - Chemistry XXI Unit 1 How do we analyze a system?...

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Unformatted text preview: Chemistry XXI Unit 1 How do we analyze a system? Searching for Differences Chemistry XXI Lab Session 2 How do we identify an unknown substance? Chemistry XXI Chemical thinking and practices are very useful in determining the identity and analyzing the properties of chemical substances. Detection: Does the sample contain substance X? Identification: What is the identity of the substance in this sample? Central Goals and Questions Separation: How can the substances present in the sample be separated? Quantitation: How much of substance X is in the sample? The Motives These are the types of questions we want to answer. Chemistry XXI Imagine that you are employed by a recycling firm. You have been assigned to devise a quick and cheap method for identifying different types of plastics. The Challenge What beginning questions do you need to answer to complete your job? Given these unknown samples of plastics: Chemistry XXI Beginning Questions Examples: Are all of the samples the same type of plastic? What is the identity of each plastic? What properties can be measured to distinguish one type of plastic from another? How do we best measure these properties (accuracy and precision)? What resources do I have to complete the task? Chemistry XXI The Resources Pure samples of known plastics. Balances (TC 4). Vernier calipers. Glassware. These are the resources you have available to complete your task: Chemistry XXI Initial Decisions Given the resources available, discuss in your groups how you propose to answer the central question for this lab: What is the identity of the unknown plastics? What differentiating characteristic would you use? What will you measure? How will you measure it? What would you do with these measurements? How will you stay safe? Chemistry XXI Trial Tests Let′s explore! As a class, decide which groups will be determining the value of the property that differentiates the different reference plastics. What should each group do? How can you ensure reproducibility of measurements? How can you determine what technique is best? You have 30 minutes Available resources: Pure samples of known plastics. Balances (TC 4). Vernier calipers. Glassware. Chemistry XXI The tools you use needs to measure the property that you want (length, volume, etc.) The tools need to measure in the range you need ( accuracy )....
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This note was uploaded on 04/09/2009 for the course CHEM 151 taught by Professor Staff during the Fall '08 term at Arizona.

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LS2_a - Chemistry XXI Unit 1 How do we analyze a system?...

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