Transcript Document
SCIENTIFIC MEASUREMENT
Reporting Measurements
• Using significant figures
• Report what is known with
certainty
• Add ONE digit of
uncertainty (estimation)
Davis, Metcalfe, Williams, Castka, Modern Chemistry, 1999, page 46
The instrument determines the
amount of precision of the data.
• What is the certain measurement here?
• What is the estimated measurement here?
Using Significant Figures reflects
precision by estimating the last digit
• What is the certain measurement?
• What is the estimated measurement?
Example B
Measurements in the Lab:
Example A
30 mL
40 mL
20 mL
10 mL
30 mL
35.5 mL
13 mL
Example C
0
mL
1 mL
0.67 mL
2 mL
20 mL
Practice Measuring
Timberlake, Chemistry 7th Edition, page 7
0
cm
1
2
3
4
5
4.5 cm
0
cm
1
2
3
4
5
4.54 cm
0
cm
1
2
3
4
5
3.0 cm
Finding VOLUME
Finding VOLUME
What is VOLUME?
The amount of space
that a 3-dimensional
object or substance
takes up. Anything that
exists is made of matter
and therefore has
volume…(takes up
space)
The OBJECTS
The OBJECTS
Formula/Equation?
Volume = L xW x H
Length = 6cm
Finding Volume
Volume = L x W x H
Length = 6cm
Height = 4cm
Finding Volume
Volume = L x W x H
Length = 6cm
Width = 2cm
Height = 4cm
Finding Volume
Volume = L x W x H
Length = 6cm
Width = 2cm
Height = 4cm
Volume = L x W x H =
6 cm x 2 cm x 4 cm =
48
3
cm
So, the VOLUME (the amount of
space that this 3 dimensional
3
object takes up) is 48 cm
The OBJECTS
Find the VOLUME
The METHOD –
Finding Volume by Water
Displacement
-40mL
-35mL
-30mL
-25mL
-20mL
-15mL
-10mL
-5mL
1. Note the water level
-40mL
-35mL
-30mL
-25mL
-20mL
-15mL
-10mL
-5mL
2. Place the object in liquid
-40mL
-35mL
-30mL
-25mL
-20mL
-15mL
-10mL
-5mL
3. Watch the object displace
the water it is place into…
-40mL
-35mL
-30mL
-25mL
-20mL
-15mL
-10mL
-5mL
4. Note difference in water level
-40mL
-35mL
-30mL
-25mL
-20mL
-15mL
-10mL
-5mL
The water level changed 15mL
35 mL
-20 mL
15 mL
-40mL
-35mL
-30mL
-25mL
-20mL
-15mL
-10mL
-5mL
We can say the rock displaced
15mL of water
But wait, it gets better!
-40mL
-35mL
-30mL
-25mL
-20mL
-15mL
-10mL
-5mL
Volume of our rock…
Density is defined as mass per unit volume. It is a
measure of how tightly packed and how heavy
the atoms are in an object. Density is the ratio of
mass to volume
You can think of Density as the amount of
stuff per unit of space
Density is the measure of the
“compactness” of a material
How close the atoms or molecules are
to each other.
More than “heaviness” - density
includes how much space an object
takes up!!
All substances have density including
liquids, solids, and gases.
We need to be able to think about
density visually, logically and
mathematically
Visually - Which one is more
dense?
• Demonstration: Atoms in a substance
• Which square is more dense? circle one
Masses are / are not equal
Volumes are / are not equal
Visually - Which one is more
dense?
• Now… which one is more dense?
Masses are / are not equal
Volumes are / are not equal
Logically - What would take up
more space? A kilogram of
feathers…..
or a kilogram of steel?
OR
Mathematically
DETERMINING DENSITY
Regular Shapes – mass, then determine the
volume by formula/equation
EX: cubes, rectangular prisms, cylinders,
spheres, cones, etc.
Irregular shapes – mass, then measure
displacement of a liquid (usually water) by
that irregularly shaped object
Since we know that 1 mL has the same
volume as 1 cm3, we can make an easy
conversion!
Density = mass (g)
volume (cm3 or mL)
Equation to Calculate a
Substance’s DENSITY
For our terms and purposes:
Mass is usually expressed in
grams
Volume usually expressed in
cubic centimeters (cm3) or
milliliters (mL)
Density may be expressed in
other units, but you will learn
about them in Physics and
Chem….
DENSITY - an important and useful
(qualitative) intensive physical
property
Density
Mercury
mass (g)
volume (cm3)
Platinum
Aluminum
13.6 g/cm3 21.5 g/cm3
2.7 g/cm3
Density Calculations of:
1. Regularly Shaped Solids:
mass = triple beam or electronic
balance
volume = measure (l x w x h)
2. Irregularly Shaped Solids:
mass = triple beam or electronic
balance
volume = water displacement
Density Calculations of:
3. Liquids:
mass = tare graduated cylinder,
mass liquid
volume = read graduated cylinder
We will perform labs on all of these types
of density calculations!
Learning Check –
Mathematical Calculations of Density
Osmium is a very dense metal. What is its
density in g/cm3 if 50.00 g of the metal
occupies a volume of 2.22 cm3?
1) 2.25 g/cm3
2) 22.5 g/cm3
3) 111 g/cm3
Learning Check –
Mathematical Calculations of Density
Placing the mass and volume of the osmium
metal into the density setup, we obtain
D = mass = 50.00 g =
volume 2.22 cm3
= 22.522522 g/cm3 = 22.5 g/cm3
Learning Check –
Mathematical Calculations of Density
Which diagram represents the correct
order of liquid layers in the cylinder?
(K) Karo syrup (1.4 g/mL), (V) vegetable
oil (0.91 g/mL,) (W) water (1.0 g/mL)
1)
W
2) W
K
K
V
V
3)
K
V
W
Learning Check –
Mathematical Calculations of Density
The density of octane, a component of
gasoline, is 0.702 g/mL. What is the mass, in
kg, of 875 mL of octane?
1) 0.614 kg
2) 614 kg
3) 1.25 kg
Learning Check –
Mathematical Calculations of Density
If blood has a density of 1.05 g/mL, how
many liters of blood are donated if 575 g of
blood are given?
1)
2)
3)
4)
0.548 L
1.25 L
1.83 L
548 L
Learning Check –
Logical Thinking about Density
Fact: Water has a density of 1.0 g/ml
and mercury (Hg) has a density of
13.6 g/ml.
Which is heavier, a quart of water or a quart
of mercury?
If we have equal volumes of two different
substances, then the one with the greater
density will have the greater mass.
►Which is heavier, a ton of
Neither
feathers or a ton of bricks?
►Which is larger?
Feathers
►If two objects have the
same mass, the one with
the higher density will be
smaller.
Factors Affecting Density
Write the relationship statements.
Temperature –
What substance is the exception to this rule?
Pressure –
Factors Affecting Density
A solid solutes dissolved into liquid solutions –
the density change depends on the
concentration and kind of substances mixed
together.
Write the relationship statement:
Factors Affecting Density
Atomic mass – Different atoms have different atomic
masses. Write the relationship statement.
Applying What You’ve Learned
– Let’s think about the Density of
Water!
Question #1: At
what temperature is
water most dense?
Find this information
on your ESRT’s! Hint:
Look for a section about the
Properties of Water…
Question #2: Use this
chart to explain why
ice floats on water.
Use data from the
chart to support your
answer!!!!
Question #3: Use this
chart to explain what
happens to average
sea level when the
ocean’s average
temperature
increases.
Density Table
SINK or FLOAT
In Water?
(D = 1.0 g/mL)
Float
Float
Float
Sink
Sink
Sink
(alcohol)
Float
(fuel)
Float
Specific Gravity
The density of a material or substance,
relative to another substance
Expressed in a ratio: water = 1.0 g/cm3
Water is the substance to which we
compare other substances
Also known as SPECIFIC GRAVITY
Since we dived the density of any
substance by 1.0 g/cm3, the specific
gravity value is equal to the density of the
substance.
What are the units for specific gravity?