# 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