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?