lab 3. outline reading a meniscus volume determination and significant figures mathematic...

VOLUME DETERMINATION AND DENSITY

Lab 3

Outline Reading a meniscus Volume determination and Significant Figures Mathematic treatment of data Safety Concerns Next Assignment Summary of Significant Figure Rules for

Glassware

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. 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.

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

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).

md

V

Mathematical Treatment of Data

% Error = x 100%(| experimental value accepted value |)

accepted value

m md V

V d

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:

m 9.9856gV 10.006 mL

d 0.9979513g/mL

% Error Calculation

6

Volume Read Volume Calculated%Error x 100%

Volume Calculated

10.00 mL 10.006 mL%Error x 100%

10.006 mL

0.00 mL%Error x 100% 0.06%

10.006 mL

Safety Concerns

Reagent:Food coloring

Health Considerations: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 quiz. Submit your Lab 3 Report at the start of next

week’s lab.

Use these rules for “Volume Read”

Graduated GlasswareLook at the glasswareFind the smallest division (graduation)Report volume to 10% of the smallest division

Volumetric GlasswareFind the glassware tolerance on the glassware or in Table 3.1Report as many zeros after the decimal point for your volume, as digits after the decimal in the tolerance