Acids, Bases, and Buffers 2: Unknown Solutions Overview Getting Started Techniques Procedure FAQ Full Lab Manual Introduction & Goals Chemistry & Background Key Questions Prelab Problems Safety Procedure In Your Write-up Appendix Experiments Index ChemLab Home		Before Lab This week, plan to spend extra time on prelab preparation. Make your prelab procedure outline or flowchart clear and complete, to cover all possible contingencies. You should meet with your partner to plan your strategy before coming to lab. Both partners should contribute to the procedure planning. Since you will plan your procedure together, the content of your prelab procedures may be very similar. Include a high level of detail in your sample calculations or analysis outline or flowchart. The better prepared you are before lab, the more smoothly your experiments will go. Be sure to complete your prelab problems. In Lab Record your observations and your data, with citation of your lab partner's notebook, if necessary. Clear and complete titration data will help you to analyze your results. For the acid and base solutions, remember that you must determine the concentration to within 3 significant figures. If time allows, repeat this determination to assess your reproducibility. Uncertainty Analysis For this week's experiment, you will have qualitative results, the identity of your solutions, and quantitative results, the concentrations of acid or base solutions. For the concentration determinations, you will do an uncertainty analysis to evaluate the precision of your results. Since your have a small number of results, a statistical analysis is not appropriate. This week, you will use significant figures as an approximate way of estimating the uncertainty in the solution concentrations that you determine. While in the lab, record the uncertainty in your volume measurements, both for buret readings and for pipets you might use for delivery of a sample for titration. Use these uncertainty values to determine the correct number of significant figures for each value your record. For example, a 20 mL volumetric pipet has an uncertainty of ±0.06 mL. Since we are using significant figures as an approximate method of handling the uncertainty, we will round this uncertainty to the nearest decimal place, 0.1 mL. Because 0.06 mL rounds up to 0.1 mL, you should record the volume delivered to the nearest tenth of a mL, or to 3 significant figures, as 20.0 mL. Use this method to determine the correct number of significant figures for all your data. Also note the number of significant figures given for the concentration of the standard acid and base solutions used for titration. For each data value, assume that the uncertainty is ±1 in the last significant decimal place. Use this uncertainty estimate to calculate a relative uncertainty in each of your measured or recorded values. To estimate the uncertainty in your results, follow the significant figure rules for addition, subtraction, multiplication, and division. These rules are summarized in the section at the beginning of this manual called Computing Uncertainty in Laboratory Data and Results. When you have finished your calculations and determined their significant figures, assume that their uncertainty is ±1 in the last significant decimal place. Use this uncertainty estimate to calculate a relative uncertainty in each of your calculated results. After Lab Your results section should include answers to the questions listed in the Introduction and goals section in the introduction of the experiment in the manual. You may wish to plot your data for the clearest presentation. If one of your unknowns is a buffer, use your data to construct a plot like that in Figure 2 from the introduction of the experiment in the manual on page 128, from last week. Using the data and information from your results section, fill in the data sheets in your manual and submit for grading.
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