Atoms, Molecules, Info, and more ( 1st Semester)

MEASUREMENTS AND SIGNIFICANT FIGURES : (Obj. 1)


- All physical measurements must be as accurate as possible.
- No physical measurement is exact.

Uncertainty: - Due to limitation of instrument
- Skill.

Numbers obtained should indicate the size of the uncertainty.

- To express the maximum precision: All digits that are known accurately.
+ One digit that is doubtful. (Estimated)
= Significant figures (digits)


Length = (a quantity: number + unit)
0 1 2 3 4 5 cm
Known accurately
Sig. Figs
Doubtful

The doubtful digit is always the _______

Philippe Brunet, Vanier College Chemistry Department, A18

, - Precision varies with instrument precision



Length: ________

0 1 2 3 4 5 cm


Precision = Position of the doubtful digit




To find position of doubtful digit: Divide smallest division by two *

Smallest division = 0.1 cm

𝟎. 𝟏 𝐜𝐦
= 𝟎. 𝟎𝟓 𝐜𝐦 Doubtful digit at the second decimal place
𝟐
Measurement is precise to two decimal places
which results in 3 sig. figs.
* To be considered only when precision is not provided

Philippe Brunet, Vanier College Chemistry Department, A18