CHAPTER 1
The Scienceof Chemistry
1.1 What Chemistry
Is About
2 1.1 What Chemistry Is About
Measurements
Using clear standards of measurements,
we can communicate more effectively
in answering simple questions.
3 1.1 What Chemistry Is About
MassHow heavy is an egg?
VolumeHow much space does an egg occupy?
DensityDoes an egg size piece of steel or
wood have the same mass?
PressureHow hard is it to crush an egg by squeezing
evenly from all sides?
Measurements
4 1.1 What Chemistry Is About
MassHow heavy is an egg?
VolumeHow much space does an egg occupy?
DensityDoes an egg size piece of steel or
wood have the same mass?
PressureHow hard is it to crush an egg by squeezing
evenly from all sides?
Measurements
5 1.1 What Chemistry Is About
Mass
The size (or volume) does not tell us how much matter there is.
6 1.1 What Chemistry Is About
Mass
1,000 g = 1 kg
Remember: Size (volume) does not tell us how much matter there is.
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Measurements
MassHow heavy is an egg?
VolumeHow much space does an egg occupy?
DensityDoes an egg size piece of steel or
wood have the same mass?
PressureHow hard is it to crush an egg by squeezing
evenly from all sides?
8 1.1 What Chemistry Is About
Volume indicates an amount of space.
The milliliter (mL) is a unit of volume.
Volume
9 1.1 What Chemistry Is About
You can measure the volume of a
liquid using a graduated cylinder.
75 mL
Volume
10 1.1 What Chemistry Is About
Volume
1 mL = 1 cm3
You can measure the volume of a
liquid using a graduated cylinder.
11 1.1 What Chemistry Is About
Measurements
MassHow heavy is an egg?
VolumeHow much space does an egg occupy?
DensityDoes an egg size piece of steel or
wood have the same mass?
PressureHow hard is it to crush an egg by squeezing
evenly from all sides?
12 1.1 What Chemistry Is About
3 blocks of equal volume
3 different mass values
plastic glass iron
Density
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density: a property of a substance that describes how
much matter the substance contains per unit volume;
typical units are grams per cubic centimeter (g/cm3).
Relationship between
mass and volume
14 1.1 What Chemistry Is About
Density
If 45 g of titanium are added to a graduated
cylinder containing 50 mL of water, what will
the cylinder read after the titanium has been
added?
15 1.1 What Chemistry Is About
If 45 g of titanium are added to a graduated cylinder containing 50 mL
of water, what will the cylinder read after the titanium has been added?
Density
Asked: Volume of graduated cylinder after adding 45 g of titanium
Given: 45 g of titanium, density of titanium d = 4.5 g/cm3, 50 mL of water
Relationships: mdV
16 1.1 What Chemistry Is About
If 45 g of titanium are added to a graduated cylinder containing 50 mL
of water, what will the cylinder read after the titanium has been added?
Density
Asked: Volume of graduated cylinder after adding 45 g of titanium
Given: 45 g of titanium, density of titanium d = 4.5 g/cm3, 50 mL of water
Relationships:
Solve:
The titanium adds 10 mL to the cylinder, which now reads 60 mL.
Answer: 60 mL
Discussion: This is an example of measurement using the displacement
method.
mdV
3 3
45 1.0
40
.51
m g mLV
d g cm cmmL
17 1.1 What Chemistry Is About
MassHow heavy is an egg?
VolumeHow much space does an egg occupy?
DensityDoes an egg size piece of steel or
wood have the same mass?
PressureHow hard is it to crush an egg by squeezing
evenly from all sides?
Measurements
18 1.1 What Chemistry Is About
Is the mass exactly 10.0 g?
We don’t know since any mass between 9.95 g and 10.05 g
would round off to 10.0 g
Accuracy and precision
Could it be 9.96 g?
10.04 g?
19 1.1 What Chemistry Is About
Accuracy and precision
Measurements that are not
accurate could lead you to the wrong conclusion.
If a measurement is not
precise, you may not be able to tell the difference
between agreement and
disagreement.
20 1.1 What Chemistry Is About
Accuracy how close a measurement is to the true
(correct) value.
Precision, how close the measured values are to
each other. These values
may be incorrect or correct.
21 1.1 What Chemistry Is About
Significant figures
Do you record 10 g or 10.0 g?
Does it make a difference?
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Significant figures
Yes, it makes a difference in precision
Do you record 10 g or 10.0 g?
Does it make a difference?
23 1.1 What Chemistry Is About
109 11
If you record “10 g”
If you record “10.0 g”
24 1.1 What Chemistry Is About
Precision and accuracy
What value should be recorded for the volume
measurement in the picture?
25 1.1 What Chemistry Is About
What value should be recorded for the volume
measurement in the picture?
Precision and accuracy
Asked: The value with the correct number
of significant figures
Given: You can estimate to a tenth of the
graduation of a cylinder or ruler
Relationships: The last digit on the right is assumed to be plus or minus
one-tenth.
26 1.1 What Chemistry Is About
Precision and accuracy
Asked: The value with the correct number
of significant figures
Given: You can estimate to a tenth of the
graduation of a cylinder or ruler
Relationships: The last digit on the right is assumed to be plus or minus
one-tenth.
Solve: The meniscus is right on 18, so estimate 18.0 mL.
Answer: 18.0 mL
Discussion: The real value is confidently known to be between 17.9
and 18.1 mL.
What value should be recorded for the volume
measurement in the picture?
27 1.1 What Chemistry Is About
1 sigfig 3 sigfigs 1 sigfig
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29 1.1 What Chemistry Is About
30 1.1 What Chemistry Is About
31 1.1 What Chemistry Is About
Science encompasses very large and very small objects.
The scientific notation is a shorthand system to write very large and very small numbers
Large Small
32 1.1 What Chemistry Is About
Scientific notation
1,500 = 15 x 100
mantissa
power of 10
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1,500 = 15 x 100
mantissa
= 102
100 = 10 x 10 = 102 exponent
Scientific notation
34 1.1 What Chemistry Is About
1,500 = 15 x 100
mantissa
= 102
1,500 = 1.5 x 1,000
= 103
mantissa
Scientific notation
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1,500 in scientific notation: 1.5 x 103
1,500 = 1.5 x 1,000
= 103
mantissa
Scientific notation
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40,000,000
= 4 x 107
3,600
= 3.6 x 103
83,100
= 8.31 x 104
Scientific notation
37 1.1 What Chemistry Is About
0.0015 = 1.5 x 0.001
mantissa
power of 10
Scientific notation
38 1.1 What Chemistry Is About
0.0015 = 1.5 x 0.001
mantissa
= 10–3
A negative exponent
means: the number is smaller than 1
does not mean: the whole number is negative
Scientific notation
39 1.1 What Chemistry Is About
0.0015 in scientific notation: 1.5 x 10–3
0.0015 = 1.5 x 0.001
mantissa
Scientific notation
= 10–3
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0.000 000 4
= 4 x 10–7
0.003 6
= 3.6 x 10–3
0.000 083 1
= 8.31 x 10–5
Scientific notation
41 1.1 What Chemistry Is About
Convert 0.00065 to scientific notation.
Scientific notation
Asked: The number in scientific notation
Given: 0.00065 as a decimal number
Relationships: 40.0001 10
42 1.1 What Chemistry Is About
Convert 0.00065 to scientific notation.
Scientific notation
Asked: The number in scientific notation
Given: 0.00065 as a decimal number
Relationships:
Answer:
40.0001 10
46.5 10
43 1.1 What Chemistry Is About
Using scientific notation on a calculator
Scientific notation
44 1.1 What Chemistry Is About
Measuring physical properties
Mass grams
Volume liters
Density grams per liter
Pressure atmospheres, psi
Precision vs. accuracy
Scientific notation
40,000,000
= 4 x 107
0.000 000 4
= 4 x 10–7