What are mass, volume, and density?

What are mass, volume, and density?
Mass - Measurement of the amount of matter
(or stuff) in an object.
• Base unit is the gram
There are 3 states
of matter:
Solid
Liquid
Gas
Measuring Mass
• Triple beam balance
Digital top-loading scale
Reading Sliders
 To maximize the number of digits in the
measurement we estimate the last
number.
Since the slider is actually about halfway between 3.3 and
3.4, we record 3.35
300 g
70 g
3.35 g
Weight and Mass
Earth
1 gravity
Nick’s
mass
Nick’s
weight
Jupiter
2.5
gravities
30kg
On orbit
0 gravity
30kg
Moon
1/6th
gravity
30kg
300N
50N
750N
0 newtons
30kg
Notice that Nick’s mass never changes. Nick is
30kg no matter where he goes!
Volume
The base unit for volume is the liter.
1) Volume of Regular Objects
5 cm
• We can find the volume of regular shapes with the
formula:
Volume = length x width x height.
3 cm
So a box 2 cm x 3 cm x 5cm would have a volume of:
30 cm3
2) Volume of Irregular Objects
• Water displacement method.
• Use a graduated cylinder to
measure the volume of
irregular objects.
• Liquids form a curved
surface in graduated
cylinders called Meniscus.
• Take your reading at the low
point of the meniscus.
43.0 ml
Water Displacement
• Pour 7 ml of water in a
graduated cylinder. If a
rock causes the level to
rise to 9 ml, the rock
must have a volume of 2
ml.
Volume units
1 cm3 = 1 ml
1 cm3 of water = 1 ml of water = 1 gram of water
Which do you think would have the
greater volume? The greater mass?
Why?
1 kg of feathers
1 kg of rocks
Water:
Mass and Volume
1ml or 1cm3 of water = 1 g of water
50 ml or 50 cm3 of water has a mass of 50 grams
1000 g
1000 ml of water would have a mass of ________?
Density
1. Density is defined as mass per unit volume.
2. It is a measure of how tightly packed the molecules are
in an object.
3. Density is the amount of matter within a certain
volume.
Density
A substance’s density DOES NOT CHANGE when the size
of the sample increases or decreases.
Al = 2.70 g/ml
A solid substance has a measured volume of
75.0 ml. At STP it has a mass of 130.5 g.
1.74 g/mL
Mg
How do I Calculate Density?
Density and specific gravity
• Density often has units of grams per cubic centimeter
(g/cm3).
• Gram is the unit for mass.
• Cm3 is the unit for volume. ***** 1ml = 1cm3
To find the density
1- Find the mass of the object
2- Find the volume of the object
3- Divide
Density = Mass g
Volume cm³
ALWAYS
REMEMBER
UNITS!
Ways to Affect Density
Change Mass AND Keep Volume Same
Increase the mass  increase density
Decrease the mass  decrease in density
Which container has more density?
A
B
Ways to Affect Density
Change Volume AND Keep Mass Same
Increase the volume  decrease density
Decrease the volume  increase density
Which container has more density?
A
B
What 2 ways will INCREASE density?
Keep the
same
mass AND
decrease
the
volume
Keep the
same
volume
AND
increase
the mass
Liquid Layers
1.
If you pour together liquids that
don’t mix and have different
densities, they will form liquid
layers.
2.
The liquid with the highest
density will be on the bottom.
3.
The liquid with the lowest
density will be on the top.
4.
Objects or substances with
MORE density will sink below
objects or substances with LESS
density.
If you have 2 or more
substances,
the MORE dense
substance will be on
bottom
The LESS dense substance
will be on top
The density of five liquids are measured as
follows:
–
–
–
–
–
Liquid 1: 1.0 g/mL
Liquid 2: 1.38 g/mL
Liquid 3: 0.77 g/mL
Liquid 4: 2.95 g/mL
Liquid 5: 0.056 g/mL
Liquid 5
Liquid 3
Liquid 1
Liquid 2
Liquid 4
Liquid Layers
Check out this picture. Which
layer has the highest density?
Which layer has the lowest
density?
Imagine that the liquids have the
following densities:
– 10g/cm3.
– 6g/cm3.
3g/cm3.
5g/cm3.
3 g/cm3
5 g/cm3
Which number would go with
which layer?
6 g/cm3
10 g/cm3
Accuracy
• How close a measured value is to an
accepted value
-Accuracy can be determined by just one
measurement
-Depends on the quality of the measuring
device
The density of water is 1.00 g/mL
and a student calculated the
density of water to be 0.99 g/mL.
Precision
•How close a series of measurements are
to one another.
-Precision is determined by more than one
measurement
-Depends on the skill of
the person measuring
The density of water is 1.00
g/mL
.89
.87
.89
.88
.88
Examples of Precision and
Accuracy:
Low Accuracy
High Precision
High Accuracy
Low Precision
High Accuracy
High Precision
Percent Error
• Accepted Value (also known as theoretical or true value)
- a quantity used by general agreement of
the scientific community
- “what you are supposed to get”
• Experimental Value (also known as the measured value)
- a quantitative value measured during an
experiment
- “what you got”
Percent Error
Error = the difference between the accepted
value and the experimental value
Percent Error = the percent that a measured
value differs from an accepted value
% Error = (What you got) – (What you were supposed to get) x 100
(What you were supposed to get)
Reference Table T
Percent Error Practice
1. The boiling point of water is 100°C. During an
experiment, water came to a boil at 97°C according to
the thermometer that was being used. What is the
percent error of the thermometer?
2. An experiment was performed to determine the density
of water. The results of the experiment showed that
water had a density of 1.15 g/mL. What was the
percent error in this experiment?
Percent Error Practice
3. An experiment was conducted to find the mass of one
mole of carbon atoms. The results of the experiment
showed that a mole of carbon atoms had a mass of
15.78 g. The accepted value of a mole of carbon atoms
is 16.00 grams. What is the percent error in this
experiment?
4. An experiment performed to determine the density of
lead yields a value of 10.95 g/cm3. The accepted value
for the density of lead is 11.342 g/cm3. Find the
percent error.
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