GenChem 2 nd Class Introduction to Measurement Make sure you are sitting with your group members! Today’s Agenda:  Safety Agreement Check  Review of notebook  Math review  Review of the experiment  Perform lab work  Analyze results (including calculations)  Discuss writing the report

GenChem Safety Agreement Have you done it? We can not let you work in our labs if you don’t agree to be safe.

GenChem  Exchange your notebook with one of your group members.  Evaluate the notebook. Is it suitable? Is it being correctly used? Share your views with the owner.  Return the notebook to its owner.  As a group, make a list of the things you expect to be putting in your notebook today. Notebooks

GenChem  As a group, make a list of the things you expect to be putting in your notebook today. Notebooks  Title, date, time, names of partners.  observations, measurements, descriptions of what was done.  signature at the end of the session.  instructor initials

GenChem Lets Practice The Amazing Oscillating Chemical Reaction Observe the reaction Characterize the reaction Determine a variable that can be measured and measure it. Plot the results and draw a conclusion. And record it all in your notebook!

GenChem Density is an intensive property that is commonly used to differentiate and separate plastics during recycling. What do you need to measure to determine the density of each of the plastic pieces? Density = mass/volume (  = m/V) mass and volume must be measured to determine density Let′s think!

GenChem Pre-lab assignments revisited

GenChemRevisiting Mass Measurement In your groups revisit what you will need to do to make reliable mass measurements. DON’T FORGET  Balances must not be moved  Only glass or metal objects can be put on the pan  They must be left clean.  Let′s think!

GenChem Volume Measurement In your groups review your responses to the following pre-lab question and come up with a consensus answer. Describe how to use a graduated cylinder to reliably and accurately measure the volume of a liquid Let′s think!

GenChem Volume Measurement: making linear measurements. In your groups your responses to the following pre-lab question and come up with a consensus answer. Lengths are measured using rulers. Describe why a vernier caliper is preferred over a common ruler for this experiment. Make sure you know how to use it! Let′s think!

GenChem Volume Measurement: linear measurements vs displacement. In your groups review your responses to the following pre-lab question and come up with a consensus answer. Which technique do you think will provide the more accurate measurement of the coin’s volume - displacement or linear measurement? Justify your choice. How could you prove one to be more accurate? Let′s think!

GenChem Volume Measurement: linear measurements. In your groups review your responses to the following pre-lab question and come up with a consensus answer. Make an outline of the operations you will have to perform to determine the volume of a coin by making linear measurements. Include all the equipment and materials you will need to use. Will this work for the plastic pieces? Modify your procedure as needed. Let′s think!

GenChem Volume Measurement: displacement. Let′s think! In your groups discuss your responses to the following pre-lab question and come up with a consensus answer. Make an outline of the operations you will have to perform to determine the volume of a coin using displacement. Include all the equipment and materials you will need to use. Will this work for the plastic pieces? Modify your procedure as needed. What if it floats?

GenChem Identifying Unknown Samples Once you have determined the density of an unknown piece of plastic, what else will you need to know to identify it? Density values for candidate plastics

GenChem Determining Known Values You will need to know the densities of the six possible plastics to identify your unknown. The following samples are provided for your use. Polyvinyl chloride ( PVC) High Density Polyethylene ( HDPE) Polyethylene terephthalate( PETE) Polypropylene ( PP)Polystyrene ( PS) Low Density Polyethylene (LDPE) Your group will be responsible for determining the density of one plastic

GenChem First Challenge Determine the density of your assigned plastic. Measure the volume both ways and compute the density separately for each. Available resources:  4 pieces of PVC.  Rulers, vernier calipers.  Balances (TC 4).  Glassware. Design a feasible procedure and implement it! Let′s explore! You have 30 minutes

GenChem Let′s think! Choose a reporter. That person is to report to the class the one value to use for that plastic, your justification for selecting that value and your confidence in that value. Within your group, review your results and decide on a value for the density of your plastic. Prepare a report to the class.

GenChem  Did everyone have the same value? If not, how did you decide on one number to report?  Did both volume determination methods produce the same value? If not, which one did you chose to use and why?  What is your confidence in your answer? Does your reported value reflect your confidence? How so? While preparing your report consider the following Let′s think!

GenChem Known values for plastic densities. Reports to the class Each group is to report.  The known value to use for that plastic.  The justification for selecting that value.  The confidence in that value. PlasticDensity (g/mL) HDPE LDPE PET PP PS PVC Let′s think!

GenChem Final Challenge Identify your unknown plastic pieces. Available resources:  Densities of known plastics  Pieces of unknown plastics.  Balances;  Rulers, vernier calipers;  Glassware; Design a feasible procedure and implement it! Let′s explore! You have 20 minutes

GenChem The Report To be submitted next week:  Results. An organized presentation of the results obtained.  Discussion. A discussion of the results obtained. For this report (only) this is to be the answers to the Wrap-up Discussion questions. You will now write your report for this experiment. It is a limited report. Only the indicated sections are required. To be submitted BEFORE leaving class:  Raw data. A copy of all measurements and observations you collected in lab.  Calculations. Examples of the various calculations performed.

GenChem Calculations From p. 65 of your Technique Book: Calculations. Examples of all calculations performed to manipulate the numerical data. Include one example for each type. From p. 70 of your Technique Book: One example for each type of calculation. Each example should consist of three parts: –The formula that describes the calculation –The formula in use –The answer

GenChem Calculations: Outline In your groups: What were the major goals of today’s lab? 1.Find densities of known plastics 2.Identify unknown plastic Let′s think!

GenChem Calculations: Outline In your groups: Identify the important calculations that should be included in your calculations section 1.Known Plastics Volume of plastic Density (can be taken from the graph rather than actually calculating) 2.Unknown Plastics Volume of plastic Density of plastic Let′s think!

GenChem Calcuations Calculations should always use a three step format: Write out the equation Plug in your numbers Give the answer This method ensures that your instructor can follow your thought process during the calculation. Do not forget to add units and watch significant figures during your calculations! Let’s apply

GenChem Calculations: Goal 1 The first calculation we listed is volume: Volume of a rectangular prism: length x width x height = volume 1.05 cm x 1.26 cm x 1.82 cm =volume volume=2.41 cm 3 Let’s apply

GenChem Calculations: Goal 1 The second calculation we have listed is density. We obtained this value from the graph, but it would be helpful to make a note in the calculations so that the reader does not think you forgot one: Density of known plastic: Determined from the slope of the graph Let’s apply

GenChem Calculations: Goal 2 The first calculation of goal 2 is the same as that of goal 1: volume. Since we have already shown this calculation, we do not need to show it again. If we calculated the volume a different way, then we would need to show a second calculation. Let’s apply

GenChem Calculations: Goal 2 The last calculation we have is density of the unknown plastic. Since we only had one piece of plastic, we do not have a graph to use to calculate density, so we have to use a formula. Density: Let’s apply

GenChem Calculations: Things to Remember Include a calculation for all types of calculations that you do, but only include one example for the type of calculation Watch significant figures and units

GenChem Results From p. 65 of your Technique Book: Results. An organized presentation of the observations and calculated results. This section is frequently dominated by figures, tables and graphs. It will contain little to no text. From pp of your Technique Book: Results. An objective and clear description of experimental findings following an appropriate order and including relevant: Tables Graphs Figures

GenChem Results:Outline In your groups: What were the major goals of today’s lab? 1.Find densities of known plastics 2.Identify unknown plastic Let′s think!

GenChem Let′s think! Results: Outline In your groups: Identify the important results that should be included in your results section 1.Known Plastics Dimensions of plastic –Linear measurement method –Displacement method Mass of plastic Density of known plastic 2.Unknown Plastics Dimensions of plastic Mass of plastic Density of unknown plastic Proposed identity of unknown plastic

GenChem Results: Goal 1 In a labeled table, compile all of the items on your list in a table that follows a logical order. Table 1. Density determination of known plastic PETE. Let’s apply

GenChem Results: Goal 1 It also might be helpful to display this information in a graph as well. If we plot the volume on the x-axis and the mass on the y-axis, the slope will be the density of the plastic. Graph 1. Known PETE mass vs. volume measurements. Let’s apply

GenChem Results: Goal 1 Sometimes, more than one table should be used to portray all of the results from a single goal. Goal 1 can be split in to two parts: A detailed table for your plastic and graph A summary table for all unknowns Let’s apply

GenChem Results: Goal 1 Table 1. Densities of known plastics Let’s apply

GenChem Results: Goal 2 Sometimes, it makes more sense to list numbers and answers in a clear order rather than putting them in a table. Density of unknown plastic: 1.38 g/cm 3 Identity of unknown plastic: PET (Polyethylene terephthalate) Let’s apply

GenChem Results: Things to Remember Only include results that are important to the conclusions that you make Be careful about the amount of significant figures you have, especially when copying tables that you’ve made from Excel

GenChem Wrap-up Discussion Explain why significant figures are important to measurement and what they signify. Of the measurements you made, which were more precise; the mass measurements or the volume measurements? Is it practical to use density to separate plastics? Explain. Propose another way to separate plastics making use of a different property than density. Let’s apply

GenChem Looking ahead to next week We’ll be investigating the phenomenon known as “absorption spectroscopy”, the most common method used to count molecules in solution. Don’t forget that you’ll need your own food sample to evaluate! Directions are in the experiment guide