Significant Figures

Significant Figures

1. All nonzero digits are significant.• Example: 145 (3 sig figs)

2. Zeroes between two significant figures are themselves significant.

• Example: 301 (3 sig figs) but 310 (2 sig figs)

3. Zeroes at the beginning of a number are never significant.

– Example: 0.692 (3 sig figs)

4. Zeroes at the end of a number are significant if a decimal point is written in the number.

• Example:1050 (3 sig figs)• Example: 4.7010 (5 sig figs)

Calculating with Significant Figures

• When addition or subtraction is performed, answers are rounded to the least significant decimal place.

• Example 1: 16.9 + 210 = Answer is NOT: 226.9Answer is: 230

• Example 2: 134 – 1.99 =Answer is NOT: 132.01Answer is: 132

Calculating with Significant Figures• When multiplication or division is performed,

answers are rounded to the number of digits that corresponds to the least number of significant figures in any of the numbers used in the calculation.

• Example 1: 125.0 x .014 = Answer is NOT: 1.75Answer is: 1.8

• Example 2: 5.49 / 5 =Answer is NOT: 1.098Answer is: 1

Density

• Density = mass / volume– What is the density of a metal that has a mass

of 5.0 g and a volume of 30.0 mL?• 0.17 g/mL

Percent Error

% error = abs value (actual – experimental) x100

actual

Example: What is the percent error if an experiment created 5.0 grams of product when it was expected to create 5.5 grams?

Answer: 9.1%