Review CHEM 132 Mid-term Exam

Review CHEM 132 Mid-term Exam - Review Approaches for CHEM...

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Review Approaches for CHEM 132 Mid-term Exam The exam will be a multiple-choice exam, probably consisting of 14 questions, 4 of which will be calculations based. Each of the first five experiments will be covered in at least two questions, one of which will be concept driven (what was the “big picture” take-home message) while the second will explore how that concept, or experimental conclusion was applied, either in the experiment in which it was introduced or in a subsequent one. Since some questions will be calculation-based, you should bring one of the tools of your trade–a non-programmable calculator–with you. You should be prepared to apply rules related to use of significant figures. What I have provided below is a brief description of each experiment; the conclusions you should have drawn from it; and a reminder of where, when and how, the ideas which came out of it were seen later in the semester. A good way to get the most out of review sessions (or visits to either my–or your TA’s office hours) would be to review your graded lab reports and see how ideas presented here jive with the answers you gave in those reports (even if you received a good grade on the report); questions related to differences between these responses may be the most informative things you could ask. I will NOT be revisiting anything written in this introductory discussion during the review sessions. Expt 1: What Have I Actually Measured? The experiment: Four pieces of volumetric glassware–a beaker, a graduated cylinder, a volumetric pipet and a buret--were used to repeatedly deliver the same volume of water. The experimental volume (the volume “thought to be delivered”) was decided upon by reading the maximum number of significant figures possible, given the volume markings on the piece of glassware. The “maximum number of significant figures” which can be read from any measuring tool was found to include every figure read directly from the markings on the tool plus one additional estimated figure. The mass of each aliquot of water delivered from a piece of glassware was determined on an analytical balance. This mass, along with known values for the density of water at the experimental temperature, was then applied to the equation for density (d = mass/vol) to calculate the “true” volume of the sample of water delivered in each case. The accuracy of each volume “thought” to be delivered was calculated by comparing that volume to the “true” volume: “True” volume ) Expt’al volume(directly read from the glassware) X 100% = % error in “True” volume accuracy The ability to reproducibly measure the same volume with a given piece of glassware (the precision) was determined by comparing the “true” volume measured by the piece more than once: “True” volume(1) ) “True” volume(2) X 100% = % error in precision Average “True” volume
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2 Conclusions: Both accuracy and precision of volume measurement are functions of the number of
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This note was uploaded on 10/05/2009 for the course CHEM 132 taught by Professor Jones during the Fall '08 term at Maryland.

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Review CHEM 132 Mid-term Exam - Review Approaches for CHEM...

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