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MatterAnd
Measurement
Chapter 1Introduction:
Matter and Measurement
K R
Chemistry, The Central Science, 12th or LSU edition
Theodore L. Brown; H. Eugene LeMay, Jr.; and Bruce E. Bursten
MatterAnd
Measurement
Roadmap:• Physical Objects (bodies, things) Matter, RadiationMatter as atoms, moleculesMatter as electrons, protons, neutrons….Matter properties
• Chemistry Science, Chemistry interested in structure and change of matter and its properties
• Science Practical aspects (units, conversions)
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MeasurementIntelliome-Prentice Hall 3
The Chemical View of Things: Matter• Matter is the physical material of the universe. It occupies space, has
specific properties (like mass) that can be observed and measured.
• Matter: Some elementary material objects (electrons, protons, neutrons) combine to form elementary substances, atoms of elements, molecules, ions etc.
• Modern chemistry works at molecular level.
MatterAnd
Measurement© 2009, Prentice-Hall, Inc.
Chemistry
In this science we study matter and the changes it undergoes.
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MeasurementIntelliome-Prentice Hall 5
What is Chemistry?• What chemists often try to do is to find
the relationships between the structure of matter and the properties of matter we observe
• Chemistry is the science that seeks to understand what matter is and what it does by studying what atoms and molecules and the subatomic objects do. In practice, chemistry is different than physics.
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MeasurementIntelliome-Prentice Hall 6
The Scientific Method
• A process for trying to understand nature by observing nature and the way it behaves, and by conducting experiments to test our ideas.
• Key Characteristics of the Scientific Method include Observation, formulation of Hypotheses, Experimentation and formulation of Laws and Theories
MatterAnd
Measurement© 2009, Prentice-Hall, Inc.
Scientific Method
The scientific method is simply a systematic approach to solving problems.
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MeasurementIntelliome-Prentice Hall 8
Scientific method- a visual presentation:
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MeasurementIntelliome-Prentice Hall 9
Laws
• Summary of observations that combines some past observations into one general statement about those observations– Law of Conservation of Mass – “In a
chemical reaction matter is neither created nor destroyed.”
• Allows you to predict future observations– So you can test the Law with
experiments• Like in any law, improved
experiments and new knowledge could indicate violations and/or extensions of previous scientific laws
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MeasurementIntelliome-Prentice Hall 10
CHEMISTRY and CHEMICAL IN THE USA
• http://www.doe.gov• http://www.nsf.gov• http://www.nist.gov• http://www.epa.gov• http://www.nih.gov
MatterAnd
Measurement
Units of Measurement
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MeasurementPrentice HAll-Intelliome 12
What is a Measurement?• quantitative
observation• comparison to an
agreed upon standard
• every measurement has a number and a unit
Project: measuring global temperatures
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MeasurementPrentice HAll-Intelliome 13
A Measurement
• the unit tells you what standard you are comparing your object property (observable) to
• the number tells you1.what multiple of the standard the object
measures
2.the uncertainty in the measurement (the procedure for the estimate of uncertainty we will see later)
MatterAnd
Measurement
SI Units
• Système International d’Unités• Uses a different base unit for each quantity
MatterAnd
Measurement
Metric System
Prefixes convert the base units into units that are appropriate for the item being measured.
MatterAnd
Measurement
Volume
• The most commonly used metric units for volume are the liter (L) and the milliliter (mL).□ A liter is a cube 1 dm
long on each side.□ A milliliter is a cube 1 cm
long on each side.
MatterAnd
Measurement
Uncertainty in Measurements
Different measuring devices have different uses and different degrees of accuracy.
MatterAnd
Measurement
Temperature:
A measure of the average kinetic energy of the particles in a sample.
MatterAnd
Measurement
Temperature• In scientific
measurements, the Celsius and Kelvin scales are most often used.
• The Celsius scale is based on the properties of water.□ 0C is the freezing point
of water.□ 100C is the boiling
point of water.
MatterAnd
Measurement
Temperature
• The Kelvin is the SI unit of temperature.
• It is based on the properties of gases.
• There are no negative Kelvin temperatures.
• K = C + 273.15
MatterAnd
Measurement
Temperature
• The Fahrenheit scale is not used in scientific measurements.
• F = 9/5(C) + 32• C = 5/9(F − 32)
MatterAnd
Measurement
Density:
Physical property of a substance
d=mV
MatterAnd
Measurement
Uncertainty in Measurement
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MeasurementPrentice HAll-Intelliome 24
Estimating the Last Digit
• for instruments marked with a scale, you get the last digit by estimating between the marks
– if possible
• mentally divide the space into 10 equal spaces, then estimate how many spaces over the indicator is
1.2 grams
MatterAnd
Measurement
Accuracy versus Precision
• Accuracy refers to the proximity of a measurement to the true value of a quantity.
• Precision refers to the proximity of several measurements to each other.
MatterAnd
Measurement
Significant Figures
• The term significant figures refers to digits that were measured.
• When rounding calculated numbers, we pay attention to significant figures so we do not overstate the accuracy of our answers.
MatterAnd
Measurement
Significant Figures: use exponential notation, or
1. All nonzero digits are significant.
2. Zeroes between two significant figures are themselves significant.
3. Zeroes at the beginning of a number are never significant.
4. Zeroes at the end of a number are significant if a decimal point is written in the number.
MatterAnd
Measurement
Significant Figures
• When addition or subtraction is performed, answers are rounded to the least significant decimal place.
• When multiplication or division is performed, answers are rounded to the number of digits that corresponds to the least number of significant figures in any of the numbers used in the calculation.
MatterAnd
Measurement
Significant Figures
Writing Numbers to Reflect Precision
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MeasurementPrentice HAll-Intelliome 30
Reporting Measurements• measurements are written to indicate
the uncertainty in the measurement• the system of writing measurements we
use is called significant figures• when writing measurements, all the
digits written are known with certainty except the last one, which is an estimate 45.872
certainestimated
45.872
MatterAnd
Measurement© 2009, Prentice-Hall, Inc.
Dimensional Analysis
• We use dimensional analysis to convert one quantity to another.
• Most commonly dimensional analysis utilizes conversion factors (e.g., 1 in. = 2.54 cm)
1 in.
2.54 cm
2.54 cm
1 in.or
MatterAnd
Measurement© 2009, Prentice-Hall, Inc.
Dimensional Analysis
Use the form of the conversion factor that puts the sought-for unit in the numerator.
Given unit desired unitdesired unit
given unit
Conversion factor
MatterAnd
Measurement© 2009, Prentice-Hall, Inc.
Dimensional Analysis
• For example, to convert 8.00 m to inches,– convert m to cm– convert cm to in.
8.00 m100 cm
1 m
1 in.
2.54 cm 315 in.
