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

Next Unit: Unit 2- Atoms