Unit 2: Basic Math for
Chemistry
Lesson 1: Significant
Figures
Do Now: Express 44,300 in scientific
notation.
Book Section: 3.1
Accuracy is how close a measurement is
to the “correct” value.
 Precision is how close measurements are
to each other.

Accuracy vs. Precision
Accuracy vs. Precision
In science, measurements have
precision, based on the tools we use.
 The precision of the numbers is
determined by the number of significant
figures there are.

Significant Figures




All non-zeroes are significant (1-9).
◦ 423
Zeroes in the beginning… NEVER!!
◦ 0.124
◦ 0.000000053
Zeroes in the middle… ALWAYS!!
◦ 1204
◦ 6.0043
◦ 0.00809
Zeroes at the end… SOMETIMES!! (if there’s a decimal
point)
◦ 12400
◦ 1.2400
◦ 30400.
Counting Significant Figures





28.6 g
3400. cm
910 m
0.04604 L
0.0067000 kg
How Many Sig Figs?
Your answer will be rounded to the
place value of the least precise of the
original numbers.

25.1 g + 2.03 g
◦ 25.1 is precise to the tenths place
◦ 2.03 is precise to the hundredths place
◦ Your answer needs to be rounded to the
tenths place.
Adding and Subtracting Sig Figs
2.099 g + 0.05681 g
 5.44 m – 2.6103 m

Practice - Adding and Subtracting
Sig Figs
2.099 g + 0.05681 g = 2.156 g
 5.44 m – 2.6103 m = 2.83 m


DON’T FORGET UNITS!!!!
Practice - Adding and Subtracting
Sig Figs
Your answer will be rounded to the same
number of sig figs as the lowest number of
sig figs by an original number.
3.05 g / 8.5 mL
◦ 3.05 g – 3 sig figs
◦ 8.3 mL – 2 sig figs – answer gets rounded
to 2 sig figs
 0.36 g/mL
 Remember...treat units like algebra

◦ Grams divided by milliliters = g/mL
Multiplying and Dividing Sig Figs
2.4 g/mL x 15.82 mL
16.25 g / 5.1442 mL
Multiplying and Dividing Sig Figs
2.4 g/mL x 15.82 mL = 38 g
16.25 g / 5.1442 mL = 3.159 g/mL
Multiplying and Dividing Sig Figs

This Week
◦ Thursday – The Metric System (3.2) – HW 2-1
Due
◦ Friday – Pd. 4 Only – Dimensional Analysis
(3.3) – HW 2-2 Due
◦ VIDEO: Drew Brees vs. Archer
HW 2-1 Due Thursday