Download Measurements and Sig Figs

MEASUREMENTS AND SIG FIGS
Chemistry 8/28/14
DRILL
Get a ruler.
 Measure the length of your agenda book. How
long is it?
 What unit did you choose? How many digits does
your measurement have? WHY??


HW: Significant Figures WS Front & Back
OBJECTIVE

IWBAT
Measure with great precision
 Use the rules to determine the number of sig figs in a
measurement
 Use the rules to add, subtract, multiply, and divide
and have the correct number of sig figs in my answer


Collect:

Bubble Lab
MEASUREMENT LAB
Do all of your measurements have the same
number of digits?
 What determines the number of digits you write
down?

WHAT ARE SIGNIFICANT FIGURES??

Please work with a partner to complete “What
are Significant Figures??” WS. You will be
deriving rules to govern numbers!
RULES FOR DETERMINING THE NUMBER OF
SIGNIFICANT FIGURES IN A GIVEN
MEASUREMENT
 If
you are given a measurement (i.e.
YOU did not measure it), you follow
these rules to calculate the number
of sig. figs.:
All non-zero digits are sig. figs (ex.
1.2300, 3004)
 Final zeros to right of decimal are sig.
figs (ex. 1.0, 1.2300)
 Zeros surrounded by significant figures
are significant (ex. 1.2300, 102, 3004)

MEASUREMENTS DETERMINE
SIGNIFICANCE
 Read
the temperature on the
thermometer.
 Is it:
75°C?
 74°C?
 74.2°C?
 How carefully CAN you read it?

80
70
60
50
40
30
 The
instrument itself determines20the
10
significance.
0
RECORD NUMBER OF SIGNIFICANT
FIGURES IN EACH MEASUREMENT
23.0
______ 23.00
0.123
______ 0.0123 ______ 0.00123 ______
102
______
1002
______ 23.004 ______
______ 102.030 ______
PRACTICE

Use Significant Figures WS to practice with
determining numbers of Sig Figs
RULE FOR ADDITION AND SUBTRACTION
WITH SIG. FIGS.
Round the sum or difference so that it has the
SAME number of DECIMAL PLACES as the
measurement having the FEWEST decimal
places.
 ex. 2.7 + 3.52 = 6.22 = 6.2

ex. 73 - 2.341 = 70.659 = 71
ex. 1001 - 0.099 = 1000.901 = 1001
ex. 2.94 + 0.06 = 3 = 3.00
correct answer shown in red box;

what you get on your calculator shown in
italics

RULE FOR MULTIPLICATION & DIVISION
WITH SIG. FIGS.
Express a product or quotient to the same
number of significant figures as the multiplied or
divided measurement having the fewer total
significant figures.
 ex. 32.43 • 2.17 = 70.3731= 70.4 (3 sig. figs.)

ex. 9574  45 = 212.7555556 = 210 (2 sig. figs.)

correct answer shown in red box;
 what you get on your calculator shown in italics

1)
4.375 g
14.62 g
327.9
g
A.
2) 3.0024L - 2.3L =
A.
+
347g
B. 346.895g
C. 346.9g
0.7024 L
B. 0.7 L
C. 0.70 L
Example 1
Example 2
5.22 m x 82.7 m =
d = 23 g / 4.44 cm3 =
a) 431.694 m2
a) 5.18018018 g/cm3
b) 432
m2
c) 431.7
m2
d) 430 m2
b) 5.18 g/cm3
c) 5.2 g/cm3
d) 5 g/cm3
INFINITE NUMBER OF SIGNIFICANT DIGITS
 Some
quantities have
an infinite number of
significant figures
because they are
definitions rather
than measurements.
 Example, by
definition 1 meter =
100.000 00…..cm
MEASUREMENT LAB – PART II
Do you think your measurements have the
correct number of sig figs?
 Return to the lab.
 Measure the quantities a second time. Write the
number of sig figs in the third column.

CLOSURE
Identify the number of sig figs in each of
these measurements:
1.
2.
3.
4.
0.01209 g
200 m
209 m
9,000,010 s