Which numbers are exact (and therefore have an unlimited number of significant figures)? a. π = 3.14 c. EPA gas mileage rating of 26 miles per gallon d. 1 gross = 144

Key Concepts

Exact Numbers

Exact numbers are values that are counted or defined rather than measured. They have an infinite number of significant figures because they are not subject to measurement uncertainty. Examples include the number of students in a classroom or defined constants like 100 centimeters in a meter.

Significant Figures

Significant figures are the digits in a number that contribute to its precision. This includes all non-zero digits, any zeros between significant digits, and trailing zeros in the decimal portion. Understanding significant figures is crucial for accurately reporting measurements and calculations in chemistry.

Measurement Uncertainty

Measurement uncertainty refers to the doubt that exists about the result of a measurement. It arises from limitations in measurement tools and techniques, affecting the number of significant figures that can be reported. Recognizing uncertainty helps in determining how precise a measurement is and how it should be communicated.