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Volume Determination and Density. Lab 3. Outline. Reading a meniscus Volume determination and significant digits Balances Mathematical treatment of data Safety Concerns Next Assignment Summary of Significant Figure Rules for Glassware. Reading a Meniscus. Meniscus and Parallax.

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## Volume Determination and Density

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**Outline**• Reading a meniscus • Volume determination and significant digits • Balances • Mathematical treatment of data • Safety Concerns • Next Assignment • Summary of Significant Figure Rules for Glassware**Reading a Meniscus**• Meniscus and Parallax**Very Important**• Every time you read a volume from a piece of glassware in lab, or report a volume for a calculation, you need to use the appropriate level of precision of the glassware used. • Study the following rules and use them correctly and consistently.**Significant Figures: Volumetric**Glassware • Use the Tolerance table on p. 98 to determine glassware tolerance, unless it is printed on the glassware. • For example: • The 50 mL volumetric flask has a tolerance of ± 0.05 mL. Whenever you use your 50 mL volumetric flask, you will always report two zeros after the decimal, i.e. 50.00 mL.**Volumetric Flask**When this volumetric flask is filled to the calibration mark, what volume should be reported?**Volumetric Pipet**When this pipet is used to dispense solution, what volume should be reported?**Volumetric Pipet**When this pipet is used to dispense solution, what volume should be reported? And to which line should the pipet be filled?**Significant Figures: Graduated**Glassware • Look at the glassware in question. • Find the smallest graduation. • Report your volume to the closest 10% of the smallest graduation.**Smallest Graduation**• A. Calculate major graduation – major graduation • B. Determine the number of spaces between two major graduations • Smallest Graduation = A / B**Reading Graduated Cylinders**What volume should be reported?**Reading Graduated Cylinders**• Smallest graduation: 0.2 mL • 10% value: 0.02 mL • Volume to the closest 10% of the SG: 6.62 mL**Reading Graduated Cylinders**What volume should be reported?**Reading Graduated Cylinders**• Smallest graduation: 5 mL • 10% value: 0.5 mL • Volume to the closest 10% of the SG: 293.5 mL**Reading Graduated Cylinders**What volume should be reported?**Reading Graduated Cylinders**• Smallest graduation: 0.5 mL • 10% value: 0.05 mL • Volume to the closest 10% of the SG: 11.50 mL**Reading Burets**What volume should be reported?**Reading Burets**• Smallest graduation: 0.1 mL • 10% value: 0.01 mL • Volume to the closest 10% of the SG: 41.15 mL**Reading Burets**What volume should be reported?**Reading Burets**• Smallest graduation: 0.1 mL • 10% value: 0.01 mL • Volume to the closest 10% of the SG: 15.48 mL**Balances**• Cleaning • Two methods of weighing • Recording of significant figures • All sample/solution preparation should be performed at your station. Balances (and related counter space) should be used for weighing only!**Density**• Mass of a substance per unit volume. • Units for today is g/mL. • Density changes with changing temperature. • As a result, volume changes (but mass stays constant unless you spill).**Mathematical Treatment of Data**% Error = x 100%**Example of Volume Calculation**• Dry mass of a 50 mL beaker: 49.2345g • Exactly 10.00 mL of water is transferred from a 10 mL graduated cylinder into a 50 mL beaker. • Mass of the 50 mL beaker with 10.00 mL of water: 59.2201g • Mass of 10 mL water: 9.9856g • Volume read: 10.00 mL (why 2 digits of precision?)**Example of Volume Calculation**• Water temperature: 21.2 ºC • Density at this temperature (p. 100): 0.9979513 g/mL • Volume Calculation:**Safety Concerns**• Reagent: • Food coloring • Health Considerations: • Avoid contact with skin and eyes. • Do not inhale vapor or spray. • Do not ingest.**Next Assignment – Lab 4:**• Read the required reading sections in your textbook and lab manual. • Complete and submit your pre-lab questions by the deadline. • Remember to study for your quiz. • Remember to complete and submit the Lab 3 report at the start of the next lab.**Lab 4 Pre-lab Questions**• If you haven’t started this pre-lab yet, do so as soon as possible. • Read the lab write-up in your manual (pp115 - 138). • Complete the pre-lab questions (pp. 138 - 150) in MicroLab™ in the SCICom lab (NSB 204), Chemistry Resource Center (CPSB 302K) or on your personal computer if you download the program. The program may be downloaded from http://www.microlabinfo.com under the Downloads link. • Take this exercise seriously. You will be required to complete a similar exercise in lab next week without help from your lab manual.**Skill Evaluations – Next Week**• Will occur after the Lab 4 in-class assignment if time allows. • Review the skill evaluation pages for graduated glassware, safety, and calibration curves.

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