Transcript Chapter 1-part 1

Chapter 1
Measurements
1.1 Units of Measurement
In chemistry we
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measure quantities.
do experiments.
calculate results.
use numbers to report measurements.
compare results to standards.
In a measurement
• a measuring tool is used to compare some dimension
of an object to a standard.
1.1 Units of Measurement
The metric system or SI (international system) is
• a decimal system based on 10.
• used in most of the world.
• used everywhere by scientists.
Volume Measurement
Volume
• is the space occupied by a
substance.
• uses the unit liter (L) in
the metric system.
• uses the unit m3 (cubic
meter) in the SI system.
• is measured using a
graduated cylinder.
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Measuring Mass
Mass: Amount of matter
in an object
 Weight: Measures the
force with which gravity
pulls on an object.
• is measured on a balance.
• uses the unit gram (g) in
the metric system.
• uses the unit kilogram
(kg) in the SI system.

Temperature Measurement
The temperature of a substance
• indicates how hot or cold it is.
• is measured on the Celsius
(C) scale in the metric system.
• on this thermometer is 18 ºC or
64 ºF.
• in the SI system uses the Kelvin
(K) scale.
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1.1 Units in the Metric System
In the metric and SI systems, one unit is used for each type of
measurement:
Measurement
Length
Volume
Mass
Time
Temperature
Metric
meter (m)
liter (L)
gram (g)
second (s)
Celsius (C)
SI
meter (m)
cubic meter (m3)
kilogram (kg)
second (s)
Kelvin (K)
All other units are derived from these fundamental
units
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Scientific Notation
Scientific Notation
• is used to write very large or
very small numbers.
• for the width of a human
hair of 0.000 008 m is
written 8 x 10-6 m.
• of a large number such as 4
500 000 s is written 4.5 x
106 s.
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Numbers in Scientific Notation
A number written in scientific notation contains a
• Coefficient (between 1 and 9)
• power of 10.
Examples:
coefficient
1.5
power of ten
x 102
coefficient
7.35
power of ten
x
10-4
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Writing Numbers in
Scientific Notation
To write a number in scientific notation,
• move the decimal point to give a number 1-9.
• show the spaces moved as a power of 10.
Examples:
52 000. = 5.2 x 10 4
0.00178 = 1.78 x 10-3
4 spaces left
3 spaces right
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Comparing Numbers in Standard
and Scientific Notation
Here are some numbers written in standard format
and in scientific notation.
Number in
Number in
Standard Format
Scientific Notation
Diameter of the Earth
12 800 000 m
1.28 x 107 m
Mass of a typical human
68 kg
6.8 x 101 kg
Length of a pox virus
0.000 03 cm
3 x 10-5 cm
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1.4 Accuracy, Precision, and
Significant Figures

Significant figures: The number of meaningful
digits in a measured or calculated quantity. They
come from uncertainty in any measurement.

Generally the last digit in a reported measurement is
uncertain (estimated).

Exact numbers and relationships (7 days in a
week, 30 students in a class, etc.) effectively have an
infinite number of significant figures.
Known & Estimated Digits
If the length is reported as 3.26 cm,
• the digits 3 and 2 are certain (known).
• the final digit, 6, is estimated (uncertain).
• all three digits (2, 7, and 6) are significant,
including the estimated digit.
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Examples
. l8. . . . l . . . . l9. . . . l . . . . l10. . cm
What is the length of the line?
1) 9.2 cm
2) 9.13 cm
3) 9.19 cm
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Examples
Classify each of the following as (1) exact or (2)
measured
numbers.
A.__Gold melts at 1064 °C.
B.__1 yard = 3 feet
C.__The diameter of a red blood cell is 6 x 10-4 cm.
D.__There are 6 hats on the shelf.
E.__A can of soda contains 355 mL of soda.
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Accuracy, Precision, and Significant
Figures
Rules for counting significant figures (left-toright):
1. Zeros in the middle of a number are like any other
digit; they are always significant.
◦
4.803 cm
4 sf
2. Rules for counting significant figures (left-toright):
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Zero at the beginning of a number are not
significant (placeholders).
0.00661 g 3 sf
or 6.61 x 10-3 g
Accuracy, Precision, and Significant
Figures
Rules for counting significant figures (left-toright):
3. Zeros at the end of a number and after the decimal
point are always significant.
55.220 K 5 sf
4.
Zeros at the end of a number and after the decimal
point may or may not be significant.
34,2000
? SF
Rounding Numbers
If the first digit you remove is 4 or less, it and all following
digits are dropped from the number
5.664 425 = 5.664 (4 s.f)
If the digit you remove is 5 or greater, the last digit of the
number is increases by 1
5.664 525 = 5.665 (4 s.f)
Adding Significant Zeros
Sometimes, a calculator displays a small whole number.
To give an answer with the correct number of significant
figures, significant zeros may need to be written after
the calculator result.
E.g 8.00 ÷ 2.00 = 4
 4.00

3 s.f
3 s.f
calculator
result
2 zeros are needed
to give 3 s.f
Multiplication and Division
When multiplying or dividing
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the final answer must have the same number of
significant figures as the measurement with the
fewest significant figures.
Example:
110.5 x 0.048 = 5.304
4 SF
2 SF
= 5.3 (rounded)
calculator
2 SF
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Addition and Subtraction
When adding or subtracting
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the final answer must have the same number of decimal
places as the measurement with the fewest decimal places.
25.2
one decimal place
+ 1.34
26.54
26.5
two decimal places
calculated answer
final answer with one decimal place
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1.5 Prefixes
A prefix
 in front of a unit increases or decreases the size of that unit.
 makes units larger or smaller than the initial unit by one or

more factors of 10.
indicates a numerical value.
prefix
1 kilometer
1 kilogram
=
=
=
value
1000 meters
1000 grams
1 microsecond
=
10-6 second
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Metric and SI Prefixes
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