Scientific Method &
Measurement Unit
Unit EQ: Why is it important to know how to use chemistry skills?
Identifying Laboratory
Equipment
EQ: Why is it important to know how to use
different types of laboratory equipment?
Identifying Laboratory Equipment Notes
 Notes at stations
 Move from station to station to complete notes
 No more than 2 students at a station at a time
Reading Scientific
Instruments
EQ: How do significant figures relate to
measurements in chemistry?
Reading a Meterstick or Metric Ruler
 Each number represents a
centimeter (cm)
 Each small line represents a
millimeter (mm)
 Always estimate to one digit
beyond the smallest line
marker
Reading a Meterstick or Metric Ruler
a. 0.00 cm
b. 1.49 cm
c. 2.26 cm
d. 3.20 cm
Reading a Graduated Cylinder
 Meniscus – curved surface of water
 caused by adhesion of water to glass
 When reading a meniscus,
 Stoop so that the water is at your eye level
 Read the volume from the bottom of the meniscus
Reading a Graduated Cylinder
Significant Figures
 Contain all certain digits and one estimated
(uncertain) digit
 Example: 36.4 mL
 The 3 and the 6 are certain; there is no
doubt there are at least 36 mL
 The 4 is uncertain; this digit is estimated,
but tells us there is close to half of another
mL
Metric Units and
Prefixes
EQ: Why is the metric system the most useful
system for measurements in chemistry?
Why the Metric System?
 The metric, or SI system of measurement is based on multiples
of 10.
 Devised in 18th century France by Lavoisier
 Standard system to be used in all countries
 Sizes in other systems differed, causing disputes among
merchants
 Based on properties of water
 On liter of water has a mass of 1 kilogram and a volume of 1
cubic decimeter.
Base Units in the SI System
 Length = meter (m)
 Mass = gram (g)
 Volume = liter (L)
 Prefix tells you how
much larger or smaller
the unit is than the
base
Writing Abbreviations in the Metric System
 Write abbreviation for prefix
 Deciliters = dL
 Write abbreviation for base
 Millimeter = mm
 Micrograms = μg
 Megagrams = Mg
 Hectometers = hm
 Nanoliters - nL
Metric Conversions
 Find the starting unit
 Count the steps to the
ending unit
 Move the decimal the
same number of spaces in
the same direction
Metric Conversions
 Convert 65 meters to
centimeters
 Starting = meters (base)
 Ending = centi Move decimal 2 places to
the right
 65 m = 6500 cm
Metric Conversions
 Convert 130 dekagrams to
decigrams
 Starting = deka Ending = deci Move decimal 2 places to
the right
 130 dag = 13 000 dg
Metric Conversions
 Convert 17 hectometers
to kilometers
 Starting = hecto Ending = kilo Move decimal 1 place to
the left
 17 hm = 1.7 km
Metric Conversions
 Convert 4.58 mL to L
 Starting = milli Ending = base
 Move decimal 3 places to
the left
 4.58 mL = 0.00458 L
Metric Conversions
 Convert 4.998 mg to kg
 Starting = milli Ending = kilo Move decimal 6 places to the
left
 4.998 mg = 0.000 004 998 kg
Metric Conversions
 Convert 34 cL to hL
 Starting = centi Ending = hecto Move decimal 4 places to
the left
 34 cL = 0.003 4 hL
Precision and Accuracy
EQ: Compare and contrast precision and accuracy.
Accuracy
 How close a measurement
or calculation is to the
actual value
 In lab, measurements are
accurate if they have less
than 10% error.
Percent Error
 Determines the accuracy of lab
data
 Don’t forget the absolute value!
Percent error is never negative.
 Theoretical = what you should
have gotten
 Actual = what you got
Precision
 How close together two
measurements are
 Or
 The number of significant
digits in a measurement
Precision vs. Accuracy