Volume determination and density Lab 3
Reading a Meniscus Meniscus and Parallax
Reading and Recording Volumes We use significant figures to indicate the accuracy and precision of glassware. Significant figures for graduated glassware are determined differently from those of non-graduated glassware. You will need to correctly apply the following rules every time you read a volume from glassware, or use a volume in a calculation, in order to appropriately incorporate the precision of the volume into the calculation.
Significant Figures: Volumetric Glassware Use the tolerance table on p. 94 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.
Reading Graduated Glassware
Reading Graduated Glassware
Reading Graduated Glassware
Reading Graduated Glassware
Reading Graduated Glassware
Reading Graduated Glassware
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 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. 96): 0.9979513 g/mL Volume Calculation:
% Error Calculation
Safety Concerns Reagent: Health Considerations: Food coloring Avoid contact with skin and eyes. Do not inhale vapor or spray. Do not ingest.
Lab 4 Reminder Complete and submit your pre-lab questions by the deadline. Study for the next quiz. Submit your Lab 3 Report at the start of next week’s lab.
Use these rules for “Volume Read” Graduated Glassware Look at the glassware Find the smallest division (graduation) Report volume to 10% of the smallest division Volumetric Glassware Find the glassware tolerance on the glassware or in Table 3.1 Report as many zeros after the decimal point for your volume, as digits after the decimal in the tolerance