ch 2 Exact vs. Measured Values, Significant Figures & Unit Conversions

Vocabulary flashcards covering key terms from the lecture on exact versus measured quantities, significant figures, rounding, unit conversions, temperature relationships, and density.

Exact Value

A quantity known with no uncertainty, usually from counting or a defined relationship (e.g., 1 ft = 12 in); treated as having unlimited significant figures.

Measured Value

A quantity obtained with an instrument; carries experimental uncertainty and a limited number of significant figures.

Significant Figures (Sig Figs)

Digits in a measured number that convey precision, including all certain digits plus one estimated digit.

Non-Zero Digit Rule

All digits 1–9 are always significant in a measured number.

Trapped Zeros

Zeros between two non-zero digits; always counted as significant figures.

Leading Zeros

Zeros to the left of the first non-zero digit; never counted as significant figures.

Trailing Zeros

Zeros to the right of the last non-zero digit; significant only when a decimal point is present.

Rounding Rule (≥ 5)

If the first dropped digit is 5 or greater, increase the last retained digit by one; if 4 or less, leave it unchanged.

Conversion Factor

A ratio of equivalent quantities (e.g., 1000 mL / 1 L) used to convert units; derived from exact values.

Dimensional Analysis

Systematic use of conversion factors to change units while canceling unwanted units.

Metric Prefix

Symbol that scales a base SI unit by a power of ten (kilo-, milli-, micro-, etc.); must be memorized for conversions.

Multiplication/Division Sig-Fig Rule

When multiplying or dividing, the result keeps the same number of significant figures as the factor with the fewest sig figs.

Addition/Subtraction Sig-Fig Rule

When adding or subtracting, the result keeps the same number of decimal places as the term with the fewest decimal places.

Unit Conversion

Process of expressing a measurement in a different unit while representing the same quantity.

Density

Physical property defined as mass divided by volume (D = m / V).

Density Units for Liquids/Solids

Commonly reported in grams per milliliter (g/mL).

Density Units for Gases

Commonly reported in grams per liter (g/L) for convenient numerical size.

Celsius (°C)

SI-accepted temperature unit; water freezes at 0 °C and boils at 100 °C at 1 atm.

Kelvin (K)

Absolute temperature scale with 0 K at absolute zero; related to Celsius by K = °C + 273.15.

Fahrenheit (°F)

Temperature scale mainly used in the U.S.; water freezes at 32 °F and boils at 212 °F.

Kelvin–Celsius Relationship

K = °C + 273.15 (exact conversion).

Celsius–Fahrenheit Relationship

°F = (°C × 1.8) + 32.

Exact Value Example

1 inch = 2.54 cm is a defined, exact relationship with infinite significant figures.

Measured Value Example

A mass read as 5.32 g on a balance; contains three significant figures due to measurement uncertainty.