Chemistry - An Introduction to General, Organic, and Biological Chemistry: Chemistry and Measurements

Chemistry and Measurements

Units of Measurement

• Scientists employ the metric system and its modification, the International System of Units (SI), as a global standard.
• The International System of Units (SI) is the official measurement system for:
  • Length
  • Volume
  • Mass
  • Temperature
  • Time

Metric and SI Units

• Table 2.1 summarizes units of measurement and their abbreviations.

Volume

• Volume: The space occupied by a substance.
• SI unit: cubic meter.
• Chemists commonly use liters (L) and milliliters (mL).
• Graduated cylinders: Tool for measuring small volumes.
• Useful relationships:
  • $1 L = 1000 mL$
  • $1 L = 1.06 qt$
  • $946 mL = 1 qt$

Length

• Length: measured in meters (m) in both metric and SI systems.
• Chemists often use centimeters (cm).
• Useful relationships:
  • $1 m = 100 cm$
  • $1 m = 39.4 in.$
  • $1 m = 1.09 yd$
  • $2.54 cm = 1 in.$

Mass

• Mass: A measure of the quantity of material in an object.
• Measured using an electronic balance.
• SI unit: kilogram (kg).
• Chemists often measure mass in grams (g).
• Useful relationships:
  • $1 kg = 1000 g$
  • $1 kg = 2.20 lb$
  • $454 g = 1 lb$

Temperature

• Temperature: Measure of how hot or cold an object feels.
• Measured on the Celsius scale.
• SI unit: Kelvin (K).
• Water freezes at $0 °C$ and boils at $100 °C$.
• The Kelvin scale starts at absolute zero, $0 K$.

Time

• Time is based on an atomic clock and is measured in seconds (s) in both the metric and SI systems.
• Stopwatch: used to measure time.