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Overview of Metric Measurements in Chemistry

Apr 5, 2025

CHEM104 Lecture Chapter 1 Overview: Metric Measurements

Types of Measurements

  • Qualitative Measurements

    • Described without numbers.
    • Examples:
      • The solution is blue.
      • Bubbles formed.
      • The texture is rough.
  • Quantitative Measurements

    • Require numbers and units.
    • Examples:
      • Length of an object: 5.25 cm.
      • Volume of gas: 15.9 m³.
      • Density of metal: 13.6 g/mL.

Common Quantitative Measurements and Units in Chemistry

Length

  • Instrument: Ruler or meter stick.
  • Units: Meters (m), kilometers (km), centimeters (cm), millimeters (mm).
  • Metric Prefixes:
    • Kilo- (k): 1000 meters
    • Centi- (c): 0.01 meters
    • Milli- (m): 0.001 meters
  • Comments:
    • Measuring area: length × width = square meters
    • Measuring volume: length × width × height = cubic meters

Mass

  • Instrument: Balance
  • Units: Kilogram (kg), gram (g), milligram (mg), centigram (cg)
  • Comments:
    • Mass is the quantity of matter.
    • Mass vs. Weight: Mass remains constant regardless of location, while weight varies with gravity.
    • Chemists often use mass and weight interchangeably on Earth.

Volume

  • Instrument: Graduated cylinder
  • Units: Milliliters (mL), liters (L), cubic centimeters (cm³), cubic decimeters (dm³)
  • Comments:
    • 1 mL = 1 cm³
    • 1 L = 1 dm³
    • Decimeter (dm): 0.1 meters

Density

  • Formula: Density = Mass / Volume
  • Units: Grams per milliliter (g/mL), grams per liter (g/L)
  • Comments:
    • Less dense objects float; more dense objects sink.
    • Density is an intensive property (does not change with sample size).

Specific Gravity

  • Definition: Ratio of densities (D/D*), where D* is the reference density (water = 1 g/mL)
  • Comments:
    • Unitless ratio.
    • Similar to density but without units.

Temperature

  • Instrument: Thermometer
  • Units: Degrees Celsius (°C), Kelvin (K)
  • Conversion: K = °C + 273

Time

  • Instrument: Clock or stopwatch
  • Units: Seconds (s), minutes, hours
  • Usage: Important for rate calculations (e.g., speed = distance/time)

Conclusion

  • This lecture covered eight different measurements crucial for calculations in chemistry.
  • It is important to refer back to these measurements and their units as needed.