Significant figures

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Uncertainty & Significant Figures

Every scientific observation involves some degree of uncertainty depending upon the limitation of the instrument used for measurement. Because perfection in physical measurement is impossible, chemistry requires a standardized way to report data. This is where the concept of significant figures becomes critically important.

What are Significant Figures?

Significant figures are equal to the number of digits in a measured value where all digits are certain except the last digit, which is uncertain. In other words, all the meaningful digits of a datum, including the single uncertain one, are called significant figures.

Rules for Determination of Significant Figures

To accurately count significant figures in chemistry problems (a common question in JEE & NEET), you must follow these 5 fundamental rules:

i

All non-zero digits are significant.

Example: 3.14 has three significant figures.

ii

The zeros to the right of the decimal point are significant.

Example: 3.0 has two significant figures.

iii

The zeros to the left of the first non-zero digit in a number are not significant.

Example: 0.02 has only one significant figure.

iv

The zeros between two non-zero digits are always significant.

Example: 6.01 has three significant figures.

v

Exponential form: N × 10ⁿ. Only 'N' dictates the significant figures.

Example: 1.86 × 10⁴ has three significant figures.

Mastering these rules is the very first step in physical chemistry. Before advancing to complex calculations, ensure you have reviewed our complete guide on Some Basic Concepts of Chemistry.

📏 Concept Check: Significant Figures

Test your measurement accuracy skills

1. How many significant figures are present in the number 0.0045?

A) 4 B) 5 C) 2 D) 3

2. How many significant figures are in the measurement 5.030 g?

A) 2 B) 3 C) 4 D) 1

3. By definition, a measurement's significant figures include all certain digits plus:

A) Two uncertain digits B) One uncertain digit C) All decimal places D) The exponent value

4. Determine the number of significant figures in Avogadro's number: 6.022 × 10²³

A) 23 B) 27 C) 3 D) 4

5. Why do scientists use significant figures?

A) To make calculations more difficult. B) To accurately convey the uncertainty/precision of a measuring instrument. C) To eliminate all errors in an experiment. D) To balance chemical equations.

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