unit conversion chemistry 2

Measurements in Chemistry

• Measurements provide information that informs hypotheses, theories, and laws in chemistry.
• Every measurement provides three kinds of information:
  • The size or magnitude of the measurement (a number)
  • A standard of comparison for the measurement (a unit)
  • An indication of the uncertainty of the measurement

Representation of Measurements

• Measurements can be represented in different ways, including:
  • Decimal form
  • Scientific notation (also known as exponential notation)

Units in Measurements

• Units, such as liters, pounds, and centimeters, are standards of comparison for measurements.
• Examples of measurements with units:
  • A 2-liter bottle of a soft drink contains a volume of beverage that is twice that of the accepted volume of 1 liter.
  • The meat used to prepare a 0.25-pound hamburger weighs one-fourth as much as the accepted weight of 1 pound.

SI Base Units

• The seven fundamental properties ("base units") in the International System of Units (SI) are:
  • Length (meter, m)
  • Mass (kilogram, kg)
  • Time (second, s)
  • Temperature (kelvin, K)
  • Electric current (ampere, A)
  • Amount of substance (mole, mol)
  • Luminous intensity (candela, cd)

Derived SI Units

• Derived SI units can be formed by combining the base units:
  • Volume (cubic meter, m³)
  • Density (kilogram per cubic meter, kg/m³)

Prefixes in SI Units

• Prefixes can be used to create multiples and fractions of the base units:
  • Examples of prefixes: femto (10^-15), pico (10^-12), nano (10^-9), micro (10^-6), milli (10^-3), centi (10^-2), kilo (10^3), mega (10^6), giga (10^9), tera (10^12)

Density

• Density is a measure of the mass per unit volume of a substance.
• The SI unit of density is the kilogram per cubic meter (kg/m³).
• Density can be calculated by dividing the mass of a substance by its volume.

Examples of Density Calculations

• Example 1: The density of lead can be calculated by dividing its mass by its volume.
• Example 2: The density of a material can be calculated by measuring its mass and volume using the displacement of water method.### Importance of Units
• Without units, a number can be meaningless, confusing, or even life-threatening
• Example: a doctor prescribing phenobarbital without specifying units can lead to incorrect dosage and serious consequences

SI Units

• The International System of Units (SI) is a standardized system of measurement
• The seven base units of the SI system are:
  • Meter (m) for length
  • Kilogram (kg) for mass
  • Second (s) for time
  • Kelvin (K) for temperature
  • Ampere (A) for electric current
  • Mole (mol) for amount of substance
  • Candela (cd) for luminous intensity

Derived Units

• Derived units are formed by combining base units
• Examples:
  • Volume (m³)
  • Density (kg/m³)
  • Speed (m/s)

Prefixes

• Prefixes are used to represent multiples or fractions of base units
• Examples:
  • Kilo- (10³)
  • Centi- (10⁻²)
  • Milli- (10⁻³)
  • Micro- (10⁻⁶)
  • Nano- (10⁻⁹)

Measurement Conversion

• Conversions between units can be done using prefixes and base units
• Examples:
  • 1 km = 1000 m
  • 1 cm = 0.01 m
  • 1 mL = 0.001 L

Properties of Substances

• Density is a property of substances that is measured in units of mass per unit volume
• Examples:
  • Density of gold: 19.3 g/cm³
  • Density of water: 1.0 g/cm³
  • Density of air: 1.2 g/L

Calculations

• Density can be calculated by dividing mass by volume
• Example: density of lead = mass / volume = 11.3 g/cm³