Intro to Chemistry: Significant Figures!. There is uncertainty in all measurements. The “certain” digits include all numbers read directly off of the.

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Presentation transcript:

Intro to Chemistry: Significant Figures!

There is uncertainty in all measurements. The “certain” digits include all numbers read directly off of the measuring device PLUS one extra estimated digit. Ex:This device is a graduated cylinder. The units are mL. The proper reading should be: 56.0mL (estimated digit)

The amount of definite digits depends on the measuring device. An exact number has no uncertainty, and therefore has an infinite number of significant figures –Example: 25 people, …. Defined quantities are considered to be exact. Example: 12 in=1ft, 100cm=1m

Rules for Sig Figs!! 1. All non-zero digits are significant Example: s.f – 5 s.f.

2. Leading zeros are never significant (zeros to the left) Example: s.f – 1 s.f.

3. Captive zeros are always significant (zeros in the middle) Example:205 – 3 s.f – 5 s.f.

4. Trailing zeros are sometimes significant (zeros at the end) a) They are significant if the number contains a decimal point Example: – 4 s.f – 3 s.f.

4. Trailing zeros (cont.) b) They are not sig. if the number does not contain a decimal point Example: 1550 – 3 s.f – 2 s.f.

Summary (Leading) Never sig. (Captive) Always sig. (Trailing) Sometimes sig. (decimal=sig.)

Practice makes perfect! How many sig figs are in the following? , , x