If the volume of the liquid is reported to be 23.5mL, it means that digits 2 and 3 are certain while 5 is uncertain. Therefore, the number 23.5 has three significant figures. The number of significant figures conveys that except the last digits all others are correct. The number of digits depends on the precision of the scale used.
Rules for Determining the Number of Significant Figures
- All non-zero digits are significant. For example, 6.9 has two significant figures, while 2.16 has three significant figures. The decimal place does not determine the number of significant figures.
- A zero becomes significant in case it comes in between non zero numbers. For example, 2.003 has four significant figures, 4.02 has three significant figures.
- Zeros at the beginning of a number are not significant. For example, 0.002 has one significant figure while 0.0045 has two significant figures.
- All zeros placed to the right of a number are significant. For example, 16.0 has three significant figures, while 16.00 has four significant figures. Zeros at the end of a number without decimal point are ambiguous.
- In exponential notations, the numerical portion represents the number of significant figures. For example, 0.00045 is expressed as 4.5 x 10-4 in terms of scientific notations. The number of significant figures in this number is 2, while in Avogadro's number (6.023 x 1023) it is four.
- The decimal point does not count towards the number of significant figures. For example, the number 345601 has six significant figures but can be written in different ways, as 345.601 or 0.345601 or 3.45601 all having same number of significant figures.
