Unit 1.5- Sig figs, Chemical Vs. Physical, and E/C/M.

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Significant figures:

are digits within a number that help determine how accurate a data value or measurement is.

Accuracy Vs. Precision:

  • High Accuracy and High Precision- Multiple correct answers.
  • Low Accuracy and High Precision- Multiple incorrect answers (similar answers).
  • High Accuracy and Low Precision- Varied correct answers.
  • Low Accuracy and Low Precision- Varied incorrect answers.

Rules for sig figs:

  • All numbers that are not zero are significant
  • Zeros in the middle of non-zero numbers are significant
  • Zeros after the decimal are significant
  • Zeros and coefficients in scientific notations are significant
  • Leading or beginning zeros are NOT significant
  • Zeros in a larger number without a decimal are NOT significant

Math rules for sig figs:

  • When adding or subtracting round/look for the least amount of decimal places.
  • When multiplying and dividing look for the least amount of sig figs.

Examples for Sig Figs:

  • Normal examples:   * 2.2 cm = 2 sig figs   * 2.22cm = 3 sig figs   * 100.3cm= 4 sig figs   * 25.2 mL= 3 sig figs   * 1002= 4 sig figs
  • Weird examples:   * 1000 cm= 1 sig fig   * 1000,= 4 sig figs (, = decimal)

Physical Vs. Chemical:

Physical Change: Does not alter the substance (Changes appearance)

Chemical change: You can never go back to the original substance.

Physical properties (Changes):

  • Freezing and Boiling points (Phases changes)
  • Densities
  • Appearance
  • Ductile (Can be pulled into wire)/ Malleability (Can be flattened into sheets)
  • Brittle

Chemical properties (Changes):

  • Will it burn?
  • What other elements or compounds does it combine with to make compounds?
  • Will it dissolve in water? (Maybe Acid?)   * Determined by the makeup (Protons/ electrons) of the substance.

Elements/ Compounds/ Mixtures:

Elements:

  • Have certain physical and chemical properties that make them what they are   * They can be identified by those properties.     * Density (Physical)     * number of protons/ Atomic number (Chemical)

Compounds:

  • Two or more elements that have been chemically combined   * Done through bonding
  • Examples:   * H20 (water), CO2 (Carbon Dioxide), CO (Carbon monoxide)
  • Can be separated by chemical reactions.

Mixtures:

  • Any of the substances before that have been physically combined.
  • Homogenous- Uniform, same layer (Homo= Same)
  • Heterogenous- Not uniform, seperate layers (Hetero = different)
  • Aqueous mixtures (Aqueous meaning water)   * aq= dissolved in water

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Next Unit: Unit 2- Atoms

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