Chemistry lectures 3

• SI Units

  Seven basic quantities to quantify matter in our universe: Mass (m) in kg, Length (l) in m, Time (t) in sec, Electric Current (i) in A, Temperature (T) in K, Mole (n) in mol, Luminous Intensity in Cd
• Measurement conversions


  1. Collection of data is important

  2. Measurement tools and practices are crucial

  3. In calculations involving conversion from one unit to another, the unit factor is used
• Data analysis


  • Qualitative and quantitative analysis
  • Converted to information to communicate via statistical tools
• Significant figures


  Help to convey degree of accuracy of data
• Scientific notation


  Conveniently expresses very small or very large numbers
• Mass


  Determined by dividing the weight of an object by 9.8 m/s^2 (the acceleration of gravity on the surface of the earth)
• Volume


  The space the mass occupies
• Density


  The mass per unit of volume, depends on the phase and temperature
• Precision


  Describes the consistency of a series of measurements, has nothing to do with accuracy
• Accuracy


  A measure of the agreement between an accepted true value and a measured result
• Uncertainty


  The reservation on accuracy of measurements due to instruments used
• Random error


  Due to human factor, minimized by taking replicates
• Systematic error


  Due to instrument limitations, minimized by constant calibration, controlled experiment, use of better methods
• Error calculations


  1. Actual error (absolute) = True value - measured value

  2. Relative or fractional error = actual error/True value

  3. % error = Relative error x 100
• Calculations involving uncertainty


  1. When adding or subtracting, add actual errors

  2. When multiplying or dividing, add percentage errors
• Measurements & Measuring Instruments

  • Mass, Volume, Density, Specific gravity, Temperature, Pressure, Force, Concentration
• Scientific Method


  • A commonsense approach to developing and understanding of natural phenomena
  • Begins with observations that raise questions
  • Involves searching for answers, planning experiments, making observations, organizing facts to make generalizations (laws)
  • Theoretical models are required to explain why matter behaved the way it did
  • Hypotheses are tentative explanations that undergo more tests to readjust the model
  • A theory is formed after a model has survived repeated testing
  • The Scientific Method is cyclical
• The Scientific Method is used by scientists (biologists, chemists, engineers) as well as non-scientists (mechanics, financial analysts)