Chemical Foundations

1
Chemical Foundations
2
Nature of Measurement
Measurement - quantitative observation
consisting of 2 parts

• Part 1 - number
• Part 2 - scale (unit)
• Examples
• 20 grams
• 6.63 x 10-34 Joule seconds

3
Uncertainty in Measurement

• A digit that must be estimated is called
  uncertain. A measurement always has some degree
  of uncertainty.

• Measurements are performed with
• instruments
• No instrument can read to an infinite
• number of decimal places

4
Ex Reading a Meterstick

• . l2. . . . I . . . . I3 . . . .I . . . . I4. .
  cm
• First digit (known) 2 2.?? cm
• Second digit (known) 0.7 2.7? cm
• Third digit (estimated) between 0.05- 0.07
• Length reported 2.75 cm
• or 2.74 cm
• or 2.76 cm

5
Rules for Counting Significant Figures - Details

• 1. Nonzero integers always count as significant
  figures.
• 3456 has
• 4 sig figs.

6
Rules for Counting Significant Figures - Details

• Zeros
• - 2. Leading zeros do not count as
• significant figures.
• 0.0486 has
• 3 sig figs.

Note leading means ANY zero that appears
before the first nonzero digit, whether the
zeros are before OR after a decimal.
7
Rules for Counting Significant Figures - Details

• Zeros
• - 3. Sandwiched zeros always count as
• significant figures.
• 16.07 has
• 4 sig figs.

Note sandwiched means zeros that appears
between nonzero digits
8
Rules for Counting Significant Figures - Details

• Zeros
• 4. Trailing zeros are significant only if the
  number contains a decimal point.
• 9.300 has
• 4 sig figs.

Note trailing means ALL zeros that appear
after the last nonzero digit
9
Rules for Counting Significant Figures - Details

• 5. Exact numbers have an infinite number of
  significant figures.
• 1 inch 2.54 cm, exactly

10
Sig Fig Practice 1
How many significant figures in each of the
following?
1.0070 m ?
5 sig figs
17.10 kg ?
4 sig figs
100,890 L ?
5 sig figs
3.29 x 103 s ?
3 sig figs
0.0054 cm ?
2 sig figs
3,200,000 ?
2 sig figs
11
Rules for Significant Figures in Mathematical
Operations

• 1.Multiplication and Division sig figs in
  the result equals the number in the least precise
  measurement used in the calculation.
• 6.38 x 2.0
• 12.76 ? 13 (2 sig figs)

12
Sig Fig Practice 2
Calculation
Calculator says
Answer
22.68 m2
3.24 m x 7.0 m
23 m2
100.0 g 23.7 cm3
4.22 g/cm3
4.219409283 g/cm3
0.02 cm x 2.371 cm
0.05 cm2
0.04742 cm2
710 m 3.0 s
236.6666667 m/s
240 m/s
5870 lbft
1818.2 lb x 3.23 ft
5872.786 lbft
2.9561 g/mL
2.96 g/mL
1.030 g x 2.87 mL
13
Rules for Significant Figures in Mathematical
Operations

• 2 Addition and Subtraction The number of
  decimal places in the result equals the number of
  decimal places in the least precise measurement.
• 6.8 11.934 18.734 ? 18.7
• (1 decimal place, 3 sig figs)

14
Sig Fig Practice 3
Calculation
Calculator says
Answer
10.24 m
3.24 m 7.0 m
10.2 m
100.0 g - 23.73 g
76.3 g
76.27 g
0.02 cm 2.371 cm
2.39 cm
2.391 cm
713.1 L - 3.872 L
709.228 L
709.2 L
1821.6 lb
1818.2 lb 3.37 lb
1821.57 lb
0.160 mL
0.16 mL
2.030 mL - 1.870 mL
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Rules for Rounding Answers

• Complete all calculations, then round ONLY the
  final answer.
• Identify the correct digit to round (the last sig
  fig).ex 18.734
• Look ONLY at the number immediately to the right
  of this digit 18.734
• If this number is 5 or greater, round the last
  sig fig up.
• If this number is less than 5, the last sig fig
  remains the same. 18.7

16
The Fundamental SI Units (le Système
International, SI)
17
SI Units
18
SI Prefixes Common to Chemistry
Prefix Unit Abbr. Exponent
Mega M 106
Kilo k 103
Deci d 10-1
Centi c 10-2
Milli m 10-3
Micro ? 10-6
Nano n 10-9
Pico p 10-12
19
Precision and Accuracy

• Accuracy refers to the agreement of a particular
  value with the true value.
• Precision refers to the degree of agreement
  among several measurements made in the same
  manner.

Precise but not accurate
Neither accurate nor precise
Precise AND accurate
20
Types of Error

• Random Error (Indeterminate Error) - measurement
  has an equal probability of being high or low.
• Systematic Error (Determinate Error) - Occurs in
  the same direction each time (high or low), often
  resulting from poor technique or incorrect
  calibration. This can result in measurements that
  are precise, but not accurate.

21
Error Analysis Practice

• Ex 1 The data collected when the same sample of
  silver was weighed five times is as follows
• 2.31g, 2.51g, 2.30g, 2.44g, 2.40g
• The actual mass of the silver is 2.71.
• Are the students measurements accurate?
• Are they precise?
• Practice Section 1.3 1.4 3, 4, 6.

22
Dimensional Analysis

• There are times when you need to change the units
  in which a measurement is expressed.
• Ex You might want to convert from hours to
  minutes.
• 6.2 hours ? minutes
• To do so, you must find the defined relationship
  between the 2 units.
• 1 hour 60 minutes

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Dimensional Analysis

• Then create a conversion factor that will cancel
  the units of your given value.

24
Conversion Factors

• Fractions in which the numerator and denominator
  are EQUAL quantities expressed in different units
• Example 1 hr. 60 min
• Factors 1 hr. and 60 min
• 60 min 1 hr.
• Which one of these conversion factors will cancel
  the units of our given value, 6.2 hours?

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Conversion Factors

• 6.2 hours x 1 hour ? Minutes
• 60 min.
• OR
• 6.2 hours x 60 min ? Minutes
• 1 hour
• The second conv. factor allows us to cancel the
  hour units (since hr appears in numerator
  denominator) so this is the one we want.

26
Multi-step Conversions

• Sometimes you must use more than one conversion
  factor.
• When there isnt a direct relationship between
  the 2 units of interest.

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Multi-step Conversions, cont.

• How many seconds are in 1.4 days?
• Unit plan days hr min
  seconds
• Defined Relationships 1 day 24 hr
• 1 hr 60 min
• 1 min 60 s
• 1.4 days x 24 hr x 60 min x 60
  s
• 1 day 1 hr 1 min
• ANSWER 120,960 s.

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Complex Conversions

• Sometimes it is necessary to convert with
  measurements that involve more than one unit!
• Ex convert 60 mi/hr into ft/sec
• 1 mile5280 ft 1 hr60 min 1 min60 sec
• 60mi x 5280 ft 1 hr x 1 min 90
  ft/sec
• hr 1 mi 60 min 60 sec 1

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Summary Dimensional Analysis

• By using dimensional analysis the UNITS ensure
  that you have the conversion right side up, and
  the UNITS are calculated as well as the numbers!
• ASSIGNMENT Study Guide, Section 1.6,
• 15-18, 24-26
• p 16-17

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Steps in the Scientific Method

• 1. Observations
• - quantitative
• - qualitative
• 2. Formulating hypotheses
• - possible explanation for the observation
• 3. Performing experiments
• - gathering new information to decide
• whether the hypothesis is valid

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Outcomes Over the Long-Term

• Theory (Model)
• - A set of tested hypotheses that give an
• overall explanation of some natural phenomenon.
• Natural Law
• - The same observation applies to many
• different systems
• - Example - Law of Conservation of Mass

32
Law vs. Theory

• A law summarizes what happens
• A theory (model) is an attempt to explain why
  it happens.

33
Converting Celsius to Kelvin
Kelvins ?C 273
C Kelvins - 273
34
Density

• Is a physical property of matter can help you
  identify unknown element samples.
• Is the amount of mass per volume.
• Often expressed in g/mL

35
Properties of Matter
Extensive properties
depend on the amount of
matter that is present.
Volume
Mass
Energy Content (think Calories!)
Intensive properties
do not depend on the
amount of matter present.
Melting point
Boiling point
Density
36
Three Phases
37
Phase Differences
Solid definite volume and shape particles
packed in fixed positions.
Liquid definite volume but indefinite shape
particles close together but not in fixed
positions
Gas neither definite volume nor definite shape
particles are at great distances from one another
Plasma high temperature, ionized phase of
matter as found on the sun.
38
Classification of Matter
39
Separation of a Mixture
The constituents of the mixture retain their
identity and may be separated by physical means.
40
Separation of a Mixture
The components of dyes such as ink may be
separated by paper chromatography.
41
Separation of a Mixture By Distillation
42
Organization of Matter
Matter
Mixtures a) Homogeneous (Solutions) b)
Heterogeneous
Pure Substances
Elements
Compounds
Atoms
Nucleus
Electrons
Protons
Neutrons
Quarks
Quarks
43
Separation of a CompoundThe Electrolysis of water
Compounds must be separated by chemical means.
With the application of electricity, water can be
separated into its elements
Reactant ? Products
Water ? Hydrogen Oxygen
H2O ? H2 O2