CHEM101: General Chemistry I

1.2: Measurement and Notation

• 1.2.1: The Metric System

  • Stephen Lower's "General Chemistry Virtual Textbook: The Measure of Matter"

    Read the "Units of Measure" section. Remember that every measurement has a numerical value associated with a unit!
    

• 1.2.2: Systeme Internationale (SI) Units

  • Stephen Lower's "General Chemistry Virtual Textbook: The Measure of Matter"

    Read "The SI Base Units" and "The SI Decimal Prefixes" sections. Note that the base unit for mass (kg) is the only "base" unit with a prefix. This arises from the fact that the "gram" is so small (i.e., a nickel weighs approximately 5 grams) that "real world" objects cannot feasibly be measured in grams. Can you imagine how many grams a table would weigh? Also, with the exception of seconds, the SI system (System International) is a base-10 system, allowing easier conversion between units.
    

• 1.2.3: Error and Uncertainty in Measurements

  • Stephen Lower's "General Chemistry Virtual Textbook: The Meaning of Measure"

    Read the "Uncertainty Is Certain!" section. Be aware that every measured value contains some uncertainty in the last digit. For example, if you are using a ruler to measure length, it is necessary to interpolate between gradations given on the ruler. This gives the uncertain digit in the measured length. While there may not be much deviation, what you estimate to be the last digit may not be the same as someone else's estimation.
    

  • 1.2.3.1: Random versus Systematic Error

    • Stephen Lower's "General Chemistry Virtual Textbook: The Meaning of Measure"

      Read the "Scatter and Error in Measured Values" section. While error is inherent to measurement, some errors are easier to detect and/or eliminate. 
      

  • 1.2.3.2: Accuracy and Precision

    • Stephen Lower's "General Chemistry Virtual Textbook: The Meaning of Measure"

      Read the "Accuracy and Precision" section. Imagine accuracy as hitting the "bulls-eye" on a dartboard every time, while precision corresponds to hitting the "triple 20" consistently. As another example, consider an analytical balance has a calibration error such that it reads 0.24 grams too high. Then even though measuring identical mass readings of a single sample would mean excellent precision, the accuracy of the measurement would be poor.
      

• 1.2.4: Significant Figures and Rounding

  • Stephen Lower's "General Chemistry Virtual Textbook: Significant Figures and Rounding Off"

    Read this webpage. The concept of significant figures, commonly referred to as "sig figs," is important when solving scientific math problems and should be carefully observed! The rules for significant figure rounding of addition and subtraction calculations are the same, but different than those for multiplication and division.