The Science of Chemistry
Measurement
Introduction



When you hear the term chemistry,
what comes to mind???
What do you think we are going to
study??
Choose two class recorders - Brainstorm concepts on the
board….
What is chemistry about??

The study of matter and the changes it
undergoes


Chemical reactions involve energy
Involves physical and chemical changes
Measurement – number and unit

Metric Base Units





Gram – mass
Sec – time
Meter – length
Mole - amount
Kelvin – temperature
Metric prefixes

Large





Tera – 1012 times larger
Giga – 109 times larger
Mega – 106 times larger
Kilo – 103 times larger
Small





Centi – 102 times smaller
Milli – 103 times smaller
Micro – 106 times smaller
Nano – 109 times smaller
Pico – 1012 times smaller
Conversions using metric prefixes


Create a metric prefix line
Practice:



How many liters are in 525 milliliters?
How many centimeters are in 0.15
meters?
How many micrograms are in 3 grams?
Taking Measurements




Mass – triple beam balance or
electronic balance
Volume – graduated cylinder
Length – ruler
Temperature – thermometer
Uncertainty in Measurement


Accuracy – how close measured
values are to the true (accepted) value
Precision – how close measured
values are to each other
Error

Random Error



Caused by unknown and unpredictable
changes in the experiment – corrected by
doing many experiments
Experimenter’s interpretation of
measurement reading
Systematic Error

Produce a result that is different from the
actual value – cannot be corrected by
repeating the experiment
Significant Figures

The measured figures and one
additional estimated digit are counted
as significant digits.

Always use significant figures in labs
and workout problems!!!!
Rules for counting sig figs
1.
2.
3.
4.
All nonzero figures are significant.
Zeros count if the number contains a
decimal AND the zero is preceded by
a nonzero digit.
Zeros between nonzero figures are
significant.
Exact numbers contain an infinite
number of sig figs.
Examples
How many sig figs are in the
measurements?
a)
b)
c)
d)
e)
f)
g)
h)
i)
j)
1.000 70 m
100 890 L
0.005 4 cm
17.10 kg
3.29 x 103 μg
3 200 000 g
6 000. cg
0.000 350
24 hrs = 1 day
60 s = 1 min
a. 6
b. 5
c. 2
d. 4
e. 3
f. 2
g. 4
h. 3
i. infinite
j. infinite
Rules for Calculating with Sig Figs
1.
2.
Multiplication/Division – Number of sig
figs in result equals the total number
of figures in the least precise
measurement.
Addition/Subtraction – Number of
decimal places in the result equals
the number of decimal places in the
least precise measurement.
Examples
Complete the following calculations.
Write answers with correct number of
significant figures.
a)
b)
c)
d)
4.00 + 3.0 =
2.5 - 0.5 =
3.2 x 2 =
10. / 2.0 =
a. 7.0
b. 2.0
c. 6
d. 5.0
Rounding
1.
2.
3.
4.
Round 357 g to 2 significant figures.
Round 65.233 cm to 3 significant
figures.
Round 0.000 684 L to 1 significant
figures.
Round 1.256 x 102 mL to 2 significant
figures.
Scientific Notation


Shorthand way of writing very large or
small measurements
Must include all significant figures
Examples

Write the following
numbers in scientific
notation.
1.
2.
3.
4.
65 000
0.000 000 85
0.000 008 00
340.
1.
2.
3.
4.
6.5 x 104
8.5 x 10-7
8.00 x 10-6
3.40 x 102
More Examples

Write in decimal notation
1.
2.
3.
4.
2 500
3.400
0.000 000 85
0.000 000 960