Reference library5 entries

Category: Exact Numbers

Understanding exact numbers that have infinite significant figures.

Avogadro’s Number and Significant Figures: Exact or Measured?

Avogadro's constant is exact in the SI: 6.02214076×10^23 mol^-1. It therefore does not limit significant figures. Measurements used to realize a mole, such as…

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The 2019 SI Redefinition: Which Constants Are Now Exact and How It Changes Sig Fig Rules

In 2019, the SI fixed exact numerical values for h, e, k, and NA, making them exact by definition; exact constants have unlimited significant…

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Why Is a Mole Exact? The Difference Between a Count and a Measurement in Chemistry

The mole is exact because the SI defines it by an exact fixed value of the Avogadro constant; however, most laboratory amounts are obtained…

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Counted Numbers vs Measured Numbers: Precision and Significant Figures

Counted numbers are exact and have infinite significant figures, while measured numbers carry uncertainty and are limited by the instrument's precision. This guide explains…

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Exact Numbers Have Infinite Significant Figures — Here’s What That Means

Exact numbers, such as counted quantities and defined conversion factors, possess an infinite number of significant figures. This article explains the rule, provides worked…

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