Chemical Foundations. Nature of Measurement Part 1 - number Part 2 - scale (unit) Examples: 20 grams...
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Transcript of Chemical Foundations. Nature of Measurement Part 1 - number Part 2 - scale (unit) Examples: 20 grams...
![Page 1: Chemical Foundations. Nature of Measurement Part 1 - number Part 2 - scale (unit) Examples: 20 grams 6.63 x 10 -34 Joule seconds Measurement - quantitative.](https://reader033.fdocuments.net/reader033/viewer/2022051516/56649f005503460f94c161f6/html5/thumbnails/1.jpg)
Chemical Foundations
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Nature of Measurement
Part 1 - numberPart 2 - scale (unit)
Examples:20 grams
6.63 x 10-34 Joule seconds
Measurement - quantitative observation consisting of 2 parts
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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
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Rules for Counting Significant Figures - Details1. Nonzero integers always count as significant figures.
3456 has 4 sig figs.
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Rules for Counting Significant Figures - Details
Note: “leading” means ANY zero that appears before the first nonzero digit, whether the zeros are before OR after a decimal.
Zeros- 2. Leading zeros do not count as
significant figures.
0.0486 has3 sig figs.
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Rules for Counting Significant Figures - Details
Zeros- 3. Sandwiched zeros
always count assignificant figures.
16.07 has4 sig figs.
Note: “sandwiched” means zeros that appears between nonzero digits
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Rules for Counting Significant Figures - Details
Zeros4. Trailing zeros are significant only if the number contains a decimal point.
9.300 has4 sig figs.
Note: “trailing” means ALL zeros that appear after the last nonzero digit
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Rules for Counting Significant Figures - Details
5. Exact numbers have an infinite number of significant figures.
1 inch = 2.54 cm, exactly
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Sig Fig Practice #1How 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
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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)
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Sig Fig Practice #2
3.24 m x 7.0 m
Calculation Calculator says: Answer
22.68 m2 23 m2
100.0 g ÷ 23.7 cm3 4.219409283 g/cm3 4.22 g/cm3
0.02 cm x 2.371 cm 0.04742 cm2 0.05 cm2
710 m ÷ 3.0 s 236.6666667 m/s 240 m/s
1818.2 lb x 3.23 ft 5872.786 lb·ft 5870 lb·ft
1.030 g ÷ 2.87 mL 2.9561 g/mL 2.96 g/mL
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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)
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Sig Fig Practice #3
3.24 m + 7.0 m
Calculation Calculator says: Answer
10.24 m 10.2 m
100.0 g - 23.73 g 76.27 g 76.3 g
0.02 cm + 2.371 cm 2.391 cm 2.39 cm
713.1 L - 3.872 L 709.228 L 709.2 L
1818.2 lb + 3.37 lb 1821.57 lb 1821.6 lb
2.030 mL - 1.870 mL 0.16 mL 0.160 mL
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The Fundamental SI Units (le Système International, SI)
Physical Quantity Name Abbreviation
Mass kilogram kg
Length meter m
Time second s
Temperature Kelvin K
Electric Current Ampere A
Amount of Substance mole mol
Luminous Intensity candela cd
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SI Units
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SI Prefixes Common to ChemistryPrefix Unit Abbr. ExponentMega 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
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Precision and AccuracyAccuracy 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.
Neither accurate nor
precise
Precise but not accurate
Precise AND accurate
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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.
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Steps in the Scientific Method
1. Observations- quantitative- qualitative
2. Formulating hypotheses- possible explanation for
the observation3. 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
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Law vs. Theory
A law summarizes what happens
A theory (model) is an attempt to explain why it happens.
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Converting Celsius to Kelvin
Kelvins = C + 273 °C = Kelvins - 273
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Properties of MatterExtensive properties
Intensive properties
Volume
MassEnergy Content (think Calories!)
depend on the amount of matter that is present.
do not depend on the amount of matter present.
Melting point
Boiling point
Density
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Three Phases
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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 positionsGas – neither definite volume nor definite shape; particles are at great distances from one anotherPlasma – high temperature, ionized phase of matter as found on the sun.
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Classification of Matter
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Separation of a Mixture
The constituents of the mixture retain their identity and may be separated by physical means.
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Separation of a Mixture
The components of dyes such as ink may be separated by paper chromatography.
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Separation of a Mixture By Distillation
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Organization of Matter
Matter
Mixtures:a) Homogeneous (Solutions)b) Heterogeneous
Pure Substances
Compounds Elements
Atoms
Nucleus Electrons
Protons Neutrons
Quarks Quarks
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Separation of a CompoundThe Electrolysis of water
Water Hydrogen + Oxygen
H2O H2 + O2
Reactant Products
Compounds must be separated by chemical means.
With the application of electricity, water can be separated into its elements