http://www.ck12.org Chapter 3. Measurements
- Jamelle performs three separate determinations of the density of a mineral sample. She gets values of 4.58
g/cm^3 , 4.79 g/cm^3 , and 4.55 g/cm^3.
a. Calculate the average value of the density of the mineral.
b. The deviation of a measured value is defined as the absolute value of the difference between the measured
value and the average value: Deviation=|measured value−average value|. Calculate the deviation for
each of the three measurements. According to the deviations, which measurement appears to be poorest
compared to the others?
c. The average deviation is the sum of all the deviations divided by the total number of measurements.
Calculate the average deviation of the three measurements.
d. When average deviation is high, does that indicate good precision or poor precision in the measurements?
Explain. - Convert a measurement of 2.75 hours to seconds. Are the required conversion factors measured or exact
quantities? - Convert 466.84 cm to inches, given that 1 inch = 2.54 cm. The conversion factor between centimeters and
inches is a measured quantity. - Perform the following calculations and round to the correct number of significant figures.
a. 78.2 g÷32 cm^3
b. 3.0 m/s×9.21 s
c. 59 g + 4 g + 0.79 g
d. 34,000 km−2430 km
e. (9.59 g + 1.098 g)÷2.313 mL
Further Reading / Supplemental Links
- TutorialontheUseofSignificantFigures: http://www.chem.sc.edu/faculty/morgan/resources/sigfigs/index.ht
ml - Another tutorial video can be found at http://www.youtube.com/watch?v=ctj07mSIJ0w.
- SignificantFiguresCalculator: http://calculator.sig-figs.com/
- Winter, Paul K.,Significant Figures. International Textbook Company, 1965.
Points to Consider
Measurements will be a constant consideration throughout your study of chemistry. Next you will begin a study of
the atom, its component parts, and the evolution of the atomic model.
- Atoms are extremely small and extremely light. How do you think that the mass and size of an atom can be
measured? Do you think the accuracy of these measurements has improved over time?