Chapter 2 - Chemistry and Measurements

2.1 - Units of Measurement

  • Physical amounts in science are described in units of the metric or international units system (SI).
  • Some of the key units include volume liter (L), length meter (m), gram (g), weight kilogram (kg), temperature degree Celsius (°C) and Kelvin (K), and time second units.

 Meterstick vs. Yardstick, Centimeters vs. Inches

2.2 - Measured Numbers and Significant Figures

  • Any number obtained by using a measuring instrument is a measured number.
    • An accurate number is obtained by counting items or from a definition.
  • The numbers reported in measurement including the estimated number are significant figures.
    • Zeros are not significant before the decimal number or at the end of the non-decimal number.

2.3 - Significant Figures in Calculations

  • The final answer is written in multiplication and division to have the same number of significant numbers as the most insignificant measurements.
    • The final answer has been written so that there is the same number of decimal places as the least decimal places measurement.

2.4 - Prefixes and Equalities

  • A prefix located before a metric or SI device changes the unit's size by 10.
    • Prefixes like centi, milli, and micro are smaller, prefixes like kilograms, megagrams, and there are large.
  • The relationship between two units, measuring identical volume, length, weight, or time, shows equal equality.

 Convestions between metric system lengths

2.5 - Writing Conversion Factors

  • To express a relation in a fraction, conversion factors are used for any relationship in the metric or in the US system, two conversion factors may be written.
    • By speaking matching components in 100 parts, a percentage is written as a conversion factor.

2.6 - Problem Solving Using Unit Conversion

  • Conversion factors are helpful if a quantity in one unit is changed to a quantity in another one.
    • A given unit is multiplied by one or more transformation factors in the problem-solving process which cancels the units until the answer has been obtained.

 Densities of different materials

2.7 - Density

  • The volume is usually g/mL or g/cm3, a ratio of its mass to the volume of the substance.
  • Conversion factors between mass and volume of a material can be written using the units of density
    • The density of a substance is comparable to the water density, 1.00 g/mL.