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.