1. Chapter 2, Section 2 “Measuring Matter”
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Weight, mass, volume & density

2. Section 2 Measuring Matter
OBJECTIVES:
Distinguish between the mass and weight of an object.

3. The International System of Units
OBJECTIVES:
List SI units of measurement and common SI prefixes.

4. Mass vs Weight 4

5. Mass is a measure of the quantity of matter present
Units of Mass
Mass is a measure of the quantity of matter present
Weight is a force that measures the pull by gravity- it changes with location
Mass is constant, regardless of location

6. Weight is the Pull of Gravity
Weight is a measure of the pull of gravity.
Weight is measured with a spring that is compressed or stretched. 6

7. All Matter has Gravity
The elephant has more matter so it has more mass, so it has more gravity.
Even dust is matter so it pulls other dust together by gravity. 7

8. Weight vs. Mass Weight changes when the pull of gravity changes
The Earth is six times the mass of the moon.
On Earth the astronaut weighs 185 lbs.
Moon has 1/6th the gravity so the astronaut weighs only 31 lbs.
Weight is not about the astronaut, it’s about the mass of object they’re standing on. 8

9. Mass is a Comparison
Mass is measured with balance, it works like a teeter totter.
Something is placed on one side.
Something else is placed on the other side till it balanced.
In the metric system everything is compared to water.
1ml H2O = 1g H2O
or 1liter H2O = 1kg H2O 9

10. Mass Does Not Change
While on the Earth I will place an object on one side of a balance and an equal amount of water on the other side.
Now I will travel to the moon.
Once on the moon I will repeat the experiment.
Although the moon pulls 1/6th as hard on the object, it also pulls 1/6th as hard on the water, so it still balances.
For this reason scientists prefer to measure matter by it’s mass not weight. 10

11. Measuring instrument is the balance scale
Working with Mass
The SI unit of mass is the kilogram (kg), even though a more convenient everyday unit is the gram
Measuring instrument is the balance scale

12. Measuring Mass – Triple-Beam Balance
1st – Place the object to be massed 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.
Click here to try an online activity.

13. _______ + ______ + _______ = ________ g
Measuring Mass
We will be using triple-beam 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: Bottom Image:

14. Measuring The numbers are only half of a measurement
Measurement = number + unit
It has a mass of 10
10 what??
Numbers without units are meaningless.
You will lose credit is you do not include your units!

15. The International System of Units
OBJECTIVES:
List SI units of measurement and common SI prefixes.

16. Section 2 Measuring Matter
OBJECTIVES:
Identify the units of volume & density
Explain how density is determined

17. International System of Units
Measurements depend upon units that serve as reference standards
The standards of measurement used in science are those of the Metric System

18. The Metric System Easier to use because it is a decimal system
Every conversion is by some power of 10.
A metric unit has two parts
A prefix and a base unit.
prefix tells you how many times to divide or multiply by 10.

19. Length
In SI, the basic unit of length is the meter (m)
Length is the distance between two objects – measured with ruler
We make use of prefixes for units larger or smaller

20. SI Prefixes – Page 74 Common to Science
Unit Abbreviation
Meaning
Exponent
Kilo- k
thousand
103
Deci- d
tenth
10-1
Centi- c
hundredth
10-2
Milli- m
thousandth
10-3
Micro- 
millionth
10-6
Nano- n
billionth
10-9

21. Volume The space occupied by any sample of matter.
Calculated for a solid by multiplying the length x width x height; thus derived from units of length.
SI unit = cubic meter (m3)
Everyday unit = Liter (L), which is non-SI. (Note: 1mL = 1cm3)

22. Recap & Review Volume is: Mass is: Weight is:
The space occupied by any sample of matter.
Mass is:
The amount of matter in an object
Weight is:
The force (or pull) of gravity on an object based on its mass
Which changes when your on the moon, your mass or weight?
Your weight
What is the SI unit for: Mass, Volume and Length
Mass = kg (kilogram)
Volume = m3 (cubic meter), we will use liters and milliliters in this class
Length = m (meter)
What is bigger a millimeter or a kilometer? By how much?
A kilometer (1000 meters) is bigger
A millimeter is 1/1000 of a meter so a kilometer is 1 million times bigger

23. Section 2 Measuring Volume & Density
OBJECTIVES:
Define what density is
Identify the units of volume & density
Explain how density is determined

24. Measuring Volume & Density
Volume is:
The space occupied by any sample of matter.
Mass is:
The amount of matter in an object
Density is ?????

25. Measuring Volume & Density
-A measure of how much matter is packed into a given volume
Which square is more dense? 25

26. Which one is more dense?
Now which one is more dense? 26

27.  how tightly packed the particles are
Density
 how tightly packed the particles are m V D
Density =
Typical units:
g/cm3 for solids
g/mL for fluids
Glass: liquid or solid?
liquids
and gases

28. Density Which is heavier- a pound of lead or a pound of feathers?
Most people will answer lead, but the weight is exactly the same
They are normally thinking about equal volumes of the two
The relationship here between mass and volume is called Density

29. Density The formula for density is: mass volume
Common units are: g/mL, or possibly g/cm3, (or g/L for gas)
Density is a physical property, and does not depend upon sample size
Density =

30. Measuring Volume
We will be using graduated cylinders to find the volume of liquids and other objects.
Read the measurement based on the bottom of the meniscus or curve. When using a real cylinder, make sure you are eye-level with the level of the water.
What is the volume of water in the cylinder? _____mL
What causes the meniscus?
A concave meniscus occurs when the molecules of the liquid attract those of the container. The glass attracts the water on the sides.
Top Image: Bottom Image:

31. Measuring Solid Volume
10 cm
9 cm
8 cm
We can measure the volume of regular object using the formula length x width x height.
_____ X _____ X _____ = _____
We can measure the volume of irregular object using water displacement.
Amount of H2O with object = ______ About of H2O without object = ______ Difference = Volume = ______
Click here for an online activity about volume. Choose Lessons  Volume & Displacement

32. Density M V
D = M
M = D x V
ass D V M D
V =
ensity
olume

33. To find volume, use… 1.
a formula
V = p r2 h
V = l w h 2.
water displacement
V = ?
Vfinal
Vinit
Vobject = Vfinal – Vinit

34. Things that are “less dense” float in things that are “more dense.”
** Density of water =
1.0 g/mL = 1.0 g/cm3
Things that are “less dense” float
in things that are “more dense.”
(And things that are “more dense” sink
in things that are “less dense.”)
D < 1 g/cm3
D > 1 g/cm3
D < 1 g/cm3
D < 1 g/cm3
The density of a liquid or solid is nearly constant,
no matter what the sample’s temperature.
Density of gases is highly dependent on temperature.

35. So why is an aircraft carrier less dense than water?
It’s mass of steel is spread across a huge volume with lots of empty space in between
Since Density = Mass/Volume
The mass of the steel spread across the huge volume gives a density < 1.0 g/cm3 (less than water)
*Things that are “less dense” float
in things that are “more dense.”
D < 1 g/cm3

36. Density of Some Common Substances (Density is a physical property of matter)
Substance Density
(g / cm3)
Air *
Lithium
Ice
Water
Aluminum
Iron
Lead
Gold
*at 0oC and 1 atm pressure

37. Two ways of viewing density
Description
This slide illustrates (density) = mass / volume relationships for gold and aluminum.
Basic Concepts
Density is an intensive property, that it, it does not depend on the size of the sample.
The density of an object can be calculated using the following formula: density = mass / volume.
The density of a substance changes with changes in temperature.
Teaching Suggestions
Use this slide to review the definition of density. Remind students that density is an intensive property. Review the equation for calculating the density of a sample.
Point out that density describes the relationship between the mass and the volume of a sample.
To make this concept more concrete, use numbers with the concept of density. In the case of aluminum and gold, there is less mass in 1 cm3 of aluminum (2.7 grams) than in 1 cm3 of gold (19.3 grams). Put another way, 1 gram of aluminum occupies a larger volume (0.37 cm3) than 1 gram of gold (0.05 cm3).
Questions
1.       What does diagram (A) show about density?
2.       What does diagram (B) show about density?
3.       Would a knowledge of density be useful in
a.     Choosing a material with which to construct a 10-kilogram barbell?
b.     Selecting a head of lettuce that will give you the most lettuce for your money if lettuce sells for 99 cents a head?
c.     Predicting whether an object would float or sink in water?
For each, explain why or why not.
4.       Suppose a 20-gram cube of aluminum were cut into four equal parts. How would the density of one part be related to the density of the whole cube?
5.       Metals expand when heated. If gold is heated, what will happen to its density? Explain.
6.       The density of ice is 0.9 g/cm3, and the density of water is 1.0 g/cm3. Suppose a glass containing ice is filled with water so the ice is even with the rim of the glass. As the ice melts, would you expect any water to spill out of the glass? Why or why not?
Dorin, Demmin, Gabel, Chemistry The Study of Matter , 3rd Edition, 1990, page 71

38. Density and Temperature
What happens to the density as the temperature of an object increases?
Mass remains the same
Most substances increase in volume as temperature increases
Thus, density generally decreases as the temperature increases

39. Density and Water
Water is an important exception to the previous statement.
Over certain temperatures, the volume of water increases as the temperature decreases (Do you want your water pipes to freeze in the winter?)
Does ice float in liquid water?
Why?

40. Note temperature and density units
- Page 90

41. Measure Density for yourself
Complete Skills Lab: Making Sense of Density
Complete skills lab data table & questions (Due tomorrow)
Complete Measuring Matter and Density Work Sheet (Due Friday)

42. Density Review

43. Density Calculations
1. A sample of lead (Pb) has mass
22.7 g and volume 2.0 cm3. Find
sample’s density. m V D =
2. Another sample of lead occupies 16.2 cm3
of space. Find sample’s mass. V
m = D V
= 184 g

44. 3. A 119.5 g solid cylinder has radius 1.8 cm and height 1.5 cm. Find
sample’s density.
1.5 cm
1.8 cm m V D
V = p r2 h
= p (1.8 cm)2(1.5 cm)
= 15.3
cm3 =

45. this object sink in water?m
8.2 cm
5.1 cm
4.7 cm
4. A 153 g rectangular solid
has edge lengths 8.2 cm,
5.1 cm, and 4.7 cm. Will
this object sink in water?
(Find object’s density and compare it to water’s density.) m V D
V = l w h
= 8.2 cm (5.1 cm)(4.7 cm)
= 197
cm3
= 0.78
< 1
No; it floats.

46. - Page 91

47. - Page 92

48. End of Section 2
Measuring Matter