Study Guide
Chapter 1 Chemistry and Measurements
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University:
Kentucky State University -
Course:
CHE 102 | General Chemistry II Academic year:
2019
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155
Pages:
35
Author:
omiliar74be
Chapter 1
Chemistry and measurements 1.1 Modern Chemistry: A Brief Glimpse
• Health and Medicine
• Sanitation systems
• Surgery with anesthesia
• Vaccines and antibiotics
• Gene therapy
•Energy and the Environment
• Fossil fuels
• Solar energy
• Nuclear energy
2 Modern Chemistry: A Brief Glimpse
• Materials and Technology
• Polymers, ceramics, liquid crystals
• Room-temperature superconductors?
• Molecular computing?
• Food and Agriculture
• Genetically modified crops
• “Natural” pesticides
• Specialized fertilizers
3 1.2 Experiment and Explanation
An experiment is an observation of natural phenomena
carried out in a controlled manner so that the results can be
duplicated and rational conclusions obtained.
A law is a concise statement or mathematical equation about
a fundamental relationship or regularity of nature.
A hypothesis is a tentative explanation of some regularity of
nature.
A theory is a tested explanation of basic natural phenomena.
Example: molecular theory of gases.
Note: We cannot prove a theory absolutely.
It is always possible that further experiments will show the theory
to be limited or that someone will develop a better theory
4 5 1.3 Law of Conservation of Mass
Antoine Lavoisier (1743–1794), a French chemist, was one of
the first to insist on the use of the balance in chemical research.
By weighing substances before and after chemical change, he
demonstrated the law of conservation of mass, which states
that “the total mass remains constant during a chemical
change (chemical reaction).”
6 7 mass – measure of the quantity of matter
SI unit of mass is the kilogram (kg)
1 kg = 1000 g = 1 x 103 g
weight – force that gravity exerts on an object
weight = c x mass
A 1 kg bar will weigh
on earth, c = 1.0
1 kg on earth
on moon, c ~ 0.1
0.1 kg on moon
8 1.4 Matter: Physical State and Chemical Constitution
There are two principal ways of classifying matter:
(1) by its physical state as a solid, liquid, or gas
(2) by its chemical constitution as an element, compound, or
mixture.
(1) Solids, Liquids, and Gases:
solid the form of matter characterized by rigidity; a solid is
relatively incompressible and has fixed shape and volume.
liquid the form of matter that is a relatively incompressible
fluid; a liquid has a fixed volume but no fixed shape.
gas the form of matter that is an easily compressible fluid; a
given quantity of gas will fit into a container of almost any size
and shape.
9 States of Matter
Solids:
Fixed shape and volume
Particles are close together
Have restricted motion
Liquids:
Fixed volume, but take
container shape
Particles are close together
Are able to flow
Gases:
Expand to fill entire container
Particles separated by lots of space
e.g., Ice, water, steam
10 (2) Elements, Compounds, and Mixtures
A physical change is a change in the form of matter but not
in its chemical identity.
Examples: Ice melting, salt or sugar dissolved in water.
(Physical property: Melting, boiling, electrical conductivity)
A chemical change, or chemical reaction, is a change in
which one or more kinds of matter are transformed into a new
kind of matter or several new kinds of matter.
Examples: rust formation, burning butane gas in oxygen
(Chemical property: Describes how a substance undergoes a
chemical reaction )
Chemical Physical
Magnesium burns when heated
Magnesium metal tarnishes in air
Magnesium metal melts at 922 K
Orange juice lightens when water
11
is added A substance: is a kind of matter that cannot be separated into
other kinds of matter by any physical process.
A mixture: is a kind of matter that can be separated by
physical means into two or more substances.
-heterogeneous mixture: a mixture that consists of
physically distinct parts, each with different properties
Example: Sand and iron filings
-homogeneous mixture (also known as a solution):
is a mixture that is uniform in its properties throughout given
samples. Examples: NaCl solution, Soft drink, Air, Solder
an Element: A substance that cannot be decomposed by any
chemical reaction into simpler substances
Fe, Au,Na etc…
A Compound: is a substance composed of two or more
elements chemically combined.
12
H2O, NaCl, CO2 13 A phase is one of several different homogeneous materials
present in the portion of matter under study.
Examples:
- Ice floating in a solution of sodium chloride in water also
consists of two phases, ice and the liquid solution.
- A heterogeneous mixture of talk powder and sugar.
14 1.5 Measurement and Significant Figures
Accuracy – how close a measurement is to the true value
Precision – how close a set of measurements are to each other
accurate
&
precise
precise
but
not accurate
not accurate
&
not precise
15 The length of the rod is just over 9.1 cm. On successive measurements, we
estimate the length by eye at 9.12, 9.11, and 9.13 cm. We record the length as
between 9.11 cm and 9.13 cm.
To indicate the precision of a measured number, we often use the concept of
significant figures.
Significant figures are those digits in a measured number (or in the result
of a calculation with measured numbers) that include all certain digits plus
a final digit having some uncertainty.
You could report the result as the average, 9.12 cm.
The first two digits (9.1) are certain; the next digit (2) is estimated, so it has
some uncertainty.
It would be incorrect to write 9.120 cm for the length of the rod. This would
say that the last digit (0) has some uncertainty but that the other digits
(9.12) are certain, which is not true.
16 Number of Significant Figures
9.12 cm 3 significant figures
9.123 cm 4 significant figures
To count the number of significant figures in a given
measured quantity, you observe the following rules:
17 Scientific Notation
The number of atoms in 12 g of carbon:
602,200,000,000,000,000,000,000
6.022 x 1023
The mass of a single carbon atom in grams:
0.0000000000000000000000199
1.99 x 10-23
N x 10n
N is non zero
Single digit number
n is a positive or
negative integer
18 Rules for Significant Figures
1. All non-zero numbers are significant.
e.g., 3.456 has (4 sig. figs)
2. Zeros between non-zero numbers
are significant.
e.g., 20089 has (5 sig. figs)
Can be written as or 2.0089 × 104 (5 sig. figs)
3. Trailing zeros always count as significant if
number has decimal point
e.g., 500. or 5.00 × 102 has 3 sig. figs
19 Rules for Significant Figures
4. Final zeros on number without decimal point
are NOT significant
e.g., 104956000
(Unknown)
5. Final zeros to right of decimal point are
significant
e.g., 3.00 has 3 sig. figs.
6. Leading zeros, to left of first nonzero digit, are
never counted as significant
e.g., 0.00012 or
1.2 × 10–4 has 2 sig. figs.
20 How many significant figures does each of the
following numbers have?
Scientific Notation # of Sig. Figs.
1.
413.97
2. 0.0006
3.
5.120063
4. 161000
5.
3600.
4.1397 × 102
5
6 × 10–4
1
5.120063
7
Unknown
3.600 × 103
4
N x 10n
N is a single
Non-zero digit
n is a positive or
negative integer
21 Q) How many significant figures are in 19.0000?
Q) How many significant figures are in 0.0005650850?
Could be rewritten as 5.650850 10-4
Rounding
22 Q)Round each of the following to three significant
figures. Use scientific notation where needed.
1. 37.459
37.5 or 3.75 × 101
2. 5431978
5.43 × 106
3. 132.7789003
133 or 1.33 × 102
4. 0.00087564
8.76 × 10–4
23 Q) Round 0.00564458 to four significant figures and
express the answer using scientific notation.
A. 5.64 10-2
B. 5.000 10-3
C. 5.645 10-4
D. 0.56446
E. 5.645 10-3
24 Significant Figures in Calculations
Multiplication and Division
• Number of significant figures in answer =
number of significant figures in least precise
measurement
e.g., 10.54 × 31.4 × 16.987
= 5621.9 = 5.62×103
4 sig. figs. × 3 sig. figs. × 5 sig. figs. = 3 sig. figs.
e.g., 5.896 ÷ 0.008 = 737 = 7×102
4 sig. figs. ÷ 1 sig. fig. = 1 sig. fig.
25 Give the value of the following calculation to the
correct number of significant figures.
635.4 0.0045
2.3589
A. 1.21213
B. 1.212
C. 1.212132774
D. 1.2
E. 1
26 Significant Figures in Calculations
Addition and Subtraction
• Answer has same number of decimal places as
quantity with fewest number of decimal
places.
e.g.,
12.9753
+319.5
+ 4.398
336.9
4 decimal places
1 decimal place
3 decimal places
1 decimal place
e.g.,
397
– 273.15
124
0 decimal places
2 decimal places
0 decimal place
27 Q) For each calculation, give the answer to the correct
number of significant figures.
1. 10.0 g + 1.03 g + 0.243 g =
2. 19.556 °C – 19.552 °C =
11.3 g or
1.13 × 101 g
0.004 °C or
4 × 10–3 °C
3. 327.5 m × 4.52 m = 1480.3 = 1.48 × 103 m2
4. 15.985 g ÷ 24.12 mL =
0.6627 g/mL or
6.627 × 10–1 g/mL
28 Q) When the expression,
412.272 + 0.00031 – 1.00797 + 0.000024 + 12.8
is evaluated, the result should be expressed as:
A. 424.06
B. 424.064364
C. 424.1
D. 424.064
E. 424
29 Q) For the following calculations, give the answer to
the correct number of significant figures.
(71.359 m 71.357 m)
(0.002 m)
(11.744 s 2 )
(3.2 s × 3.67 s)
1.
= (0.002/12)=(1.666 × 10–4 ) =2 × 10–4 m/s2
2.
(13.674 cm × 4.35 cm × 0.35 cm )
(856 s + 1531.1 s)
3
(20.818665 cm )
(2387.1 s)
= (21/2387)= 0.0088 cm3/s
Or 8.8 x 10-3
30 Exact Numbers
(1)Numbers that come from definitions
12 in. = 1 ft
60 s = 1 min
(2)Numbers that come from direct count
– Number of people in small room
• Have no uncertainty
• Assume they have infinite number of significant
figures
• The number of significant figures in a calculation
result depends only on the numbers of significant
figures in quantities having uncertainties
31 Q) If you have 9 coins in a jar. What is the total mass of the 9
coins when each coin has a mass of 3.0 grams ?
3.0 g x 9 = 27 g
The number 9 is exact and does not determine the number of
significant figures
Q) How many feet are there in 36.00 inches? Express the answer
with the correct number of significant figures: (1 ft.=12 in.)
A. 3 ft.
ft.
36.00 in
12 in.
B. 3.0 ft
C. 3.00 ft.
D. 3.000 ft.
E. 3.00000 ft.
32 Q) For the following calculation, give the answer
to the correct number of significant figures.
(14.5 cm 12.334 cm)
(2.223 cm 1.04 cm)
A. 179 cm2
B. 1.18 cm
(178.843 cm2 )
(1.183 cm)
C. 151.2 cm
= 179 / 1.18
= 151.694
=152
D. 151 cm
E. 178.843 cm2
=151.177
3 sig.fig.
=151
Note: Do not round intermediate answers !
33 (3.0 x 2.001) + 0.05
2 sig.fig x 4 sig.fig. = 2 sig.fig. = 6.0
= 6.003 + 0.05
6.0 + 0.05 = 1 d.p. + 2 d.p = 1 d.p
= 6.053
= 6.0
(no rounding)
= 6.1
(rounding) Final answer
34 a = 3.6
b = 5.01
c = 0.37
d = - 17
35
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Chapter 1 Chemistry and Measurements
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