Chemistry and Measurements

International System of Units (SI)

Official system of measurement used worldwide for length, volume, mass, temperature, and time.

Volume

Space occupied by a substance, measured in m3 in the SI system and commonly in liters (L) and milliliters (mL) by chemists.

Length

Measured in meters (m) in both metric and SI systems, and in centimeters (cm) by chemists.

Mass

Measure of the quantity of material in an object, with the SI unit of kilogram (kg) and commonly measured in grams (g) by chemists.

Temperature

Measure of how hot or cold an object feels, measured in Celsius (°C) and Kelvin (K) scales.

Time

Measured in seconds (s) in both metric and SI systems, based on an atomic clock.

Significant Figures

Digits in a measured number, including estimated digit; all nonzero numbers are significant.

Zeros Between Digits

Zeros between nonzero digits in a number are considered significant figures.

Zeros: Decimal Numbers

Zeros at the end of decimal numbers are significant figures.

Zeros: Nondecimal Numbers

Zeros used as placeholders in large numbers without a decimal point are not significant figures.

Zeros: Scientific Notation

Zeros in the coefficient of numbers in scientific notation are significant figures.

Exact Numbers

Numbers obtained by counting items or from definitions, not affecting significant figures.

Measured Numbers

Numbers obtained by measurement, influencing the number of significant figures.

Rounding Off

Adjusting a number to a specified level of precision by dropping or increasing digits.

Multiplication and Division Rule

Final answer has the same number of significant figures as the measurement with the fewest significant figures.

Adding Significant Zeros

Adding zeros to a small whole number in the result to increase precision.

cubic centimeter

A unit of volume equal to a milliliter, often used interchangeably.

kilogram

The base unit of mass in the International System of Units, equal to 1000 grams.

milligram

A unit of mass equal to one thousandth of a gram.

microgram

A unit of mass equal to one millionth of a gram.

millimeter

A unit of length equal to one thousandth of a meter.

centigram

A unit of mass equal to one hundredth of a gram.

deciliter

A unit of volume equal to one-tenth of a liter.

microliter

A unit of volume equal to one millionth of a liter.

conversion factor

A fraction used to convert between different units, ensuring units cancel out correctly.

significant figures

Digits in a number that carry meaning contributing to its precision.

percentage

A number or ratio expressed as a fraction of 100, often used as a conversion factor.

Conversion Factors

Two or more factors needed in problem-solving to complete unit changes.

Density

Compares the mass of an object to its volume; mass divided by volume.

Density: Units

Expressed in g/cm3 or g/mL for solids/liquids, and g/L for gases in the metric system.

Density of Common Substances

Densities typically given in g/cm3 or g/mL for solids/liquids and g/L for gases.

Specific Gravity

Relationship between a substance's density and water's density; calculated by dividing the sample's density by water's density.

Hydrometer

Instrument used to measure the specific gravity of fluids like urine.

Celsius

A temperature scale on which water has a freezing point of 0 degrees and a boiling point of 100 degrees