Chapter 2
Measurement Notes
Length
Scientist use the metric system—a standard
measurement system based on the #10.
The meter is the basic unit.
millimeter = mm
King
Kilo
(100 centi) centimeter = cm
Henry
Hecto
(10 deci) decimeter = dm
Died
Deca
meter = m
While
Whole
(1,000 kilo) kilometer = km
Drinking
Deci
10 mm = 1 cm
Chocolate Centi
10 cm = 1 dm
Milk
Milli
100 cm = 1m
1000 m = 1 km
Metric Units
Mass refers to the amount of matter in an
object.
The base unit of mass in the metric
system in the gram and is represented by
g.
Standard: 1 kilogram is equal to the mass
of the International Prototype Kilogram
(IPK), a platinum-iridium cylinder kept by
the BIPM at Sèvres, France.
Metric Units
Kilogram Prototype
1 Kilogram (kg) = 1000 Grams (g)
1 Gram (g) = 1000 Milligrams (mg)
Which is larger?
C. 12 milligrams or 12
A. 1 kilogram or 1500
kilograms
grams
D. 4 kilograms or 4500
B. 1200 milligrams or 1 grams
gram
Balance Rules
In order to protect the balances and ensure
accurate results, a number of rules should
be followed:
 Always check that the balance is level
and zeroed before using it.
 Do not weigh hot or cold objects.
 Clean up any spills around the balance
immediately.
Measuring Mass
We will be using triplebeam balances to find the
mass of various objects.
The objects are placed on
the scale and then you
move the weights on the
beams until you get the
lines on the right-side of
the scale to match up.
Once you have balanced the
scale, you add up the amounts
on each beam to find the total
mass.
What would be the mass of the
object measured in the picture?
_______ + ______ + _______ = ________ g
Top Image: http://www.southwestscales.com/Ohaus_Triple_Beam_750-SO.jpg
Bottom Image: http://www.regentsprep.org/Regents/biology/units/laboratory/graphics/triplebeambalance.jpg
Measuring Mass – Triple-Beam Balance
1st – Place the film canister on the scale.
2nd – Slide the large weight to the right until the arm drops below the
line. Move the rider back one groove. Make sure it “locks” into place.
3rd – Repeat this process with the top weight. When
the arm moves below the line, back it up one groove.
4th – Slide the small
weight on the front
beam until the lines
match up.
5th – Add the amounts on each beam to find the total mass to the nearest tenth of a
gram.
Check to see that the balance
scale is at zero
Volume
Volume is the amount of space a substance
occupies
The liter (L) is the base unit
Tools: metric ruler is used to measure regular
solids
v=l x w x h (cm3) or
a graduated cylinder for liquids and irregular
solids (mL)
Meniscus- the curved surface of liquid resulting
from surface tension
Graduated Cylinders
The glass cylinder
has etched marks to
indicate volumes, a
pouring lip, and
quite often, a
plastic bumper to
prevent breakage.
Reading the Meniscus
Always read volume
from the bottom of
the meniscus. The
meniscus is the
curved surface of a
liquid in a narrow
cylindrical
container.
Try to avoid parallax errors.
Parallax errors arise when a meniscus or
needle is viewed from an angle rather than
from straight-on at eye level.
Incorrect: viewing the
meniscus
from an angle
Correct: Viewing the
meniscus
at eye level
Significant Figures
 Significant figures in measurement
include the all certain digits and one
uncertain digit.
Significant figures communicate how
precise measurements are.
 Certain digits are determined
from the calibration marks on
the cylinder.
The uncertain digit (the last digit
of the reading) is estimated.
Use the graduations to find all
certain digits
There are two
unlabeled
graduations below
the meniscus, and
each graduation
represents 1 mL,
so the certain
digits of the
reading are… 52 mL.
Estimate the uncertain digit and
take a reading
The meniscus is
about eight tenths
of the way to the
next graduation,
so the final digit
in the reading is
0.8 mL
The volume in the graduated cylinder is 52.8 mL.
Self Test
Examine the meniscus below and
determine the volume of liquid
contained in the graduated cylinder.
The cylinder
contains:
7
_6
_ . 0
_ mL
Irregular Volume
A solid with an irregular volume
will be measured using the
displacement method
1. Measure and record an amount
of water
2. Drop the irregular object in the
cylinder
3. Read the cylinder again and
record the amount
4. Subtract the two measurements
and the result is the volume of
the irregular object in ml
The Thermometer
o Determine the
temperature by
reading the scale on
the thermometer at eye
level.
o Read the
temperature by using
all certain digits and
one uncertain digit.
o Certain digits are determined from the
calibration marks on the thermometer.
o The uncertain digit (the last digit of the
reading) is estimated.
o On most thermometers encountered in a
general chemistry lab, the tenths place is
the uncertain digit.
Do not allow the tip to touch the
walls or the bottom of the flask.
If the thermometer
bulb touches the flask,
the temperature of the
glass will be
measured instead of
the temperature of the
solution. Readings
may be incorrect,
particularly if the
flask is on a hotplate
or in an ice bath.
Reading the Thermometer
Determine the readings as shown below
on Celsius thermometers:
8 _
7. _
4 C
_
3
0 C
_5
_ . _
Mass
• Mass is the amount of matter in
an object
• It is determined by using a
balance
• The unit for mass is grams.
English vs. Metric Units
Which is larger?
1. 1 Pound or 100 Grams
1 pound = 453.6 grams
2. 1 Kilogram or 1 Pound
3. 1 Ounce or 1000 Milligrams
1 ounce of gold =
28,349.5 milligrams
100 kilogram =
220 pounds
Density
• The measure of how much
mass is contained in a given
volume.
The formula of density is:
Density = Mass / Volume
Comparing Densities Inferring: Which item has the
greater density?
• The bowling
ball
• Since the
bowling bowl
has a greater
mass, it has a
greater density,
even though
both balls have
the same
volume
Why is density expressed as a
combination of two different
units?
• Because density is actually
made up of two other
measurements – mass and
volume – an objects density is
expressed as a combination
of two units.
Two Common Units For
Density
• Grams per cubic centimeter
(g/cm³)
• Grams per milliliter (g/mL)
Math Practice: What is the
density of a wood block with a
volume of 125 cm³ and a mass of
57 g?
Density = mass / volume
Density = 57 g / 125 cm³
Density = 0.46 g/ cm³
Math Practice: What is the
density of a liquid with a mass
of 45 g and a volume of 48 mL?
Density = mass / volume
Density = 45 g / 48 mL
Density = 0.94 g/mL
The density of a substance is
the ______for all samples of
that substance.
• Same
An object will float if it is
_____ _____ than a
surrounding liquid.
• Less dense
Applying Concepts: How could you
use density to determine whether a
bar of metal is pure gold?
• If the bar of
gold has a
density that is
greater than or
less than 19.3
g/cm³, then the
sample is not
pure gold.
Densities of Some
Common Substances
Substance
Density
(g/cm³)
Air
0.001
Ice
0.9
Water
1.0
Aluminum
2.7
Gold
19.3
 Will an object with a density of
0.7 g/cm³ float or sink in water?
• An object that has a density
of 0.7 g/cm³ will float in water
(1 g/cm³) because it is less
dense than water