• Chemistry is the study of the properties and behavior of matter.

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Chapter 1

Introduction:

Matter and Measurement

許富銀 ( Hsu Fu-Yin)

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Why Study Chemistry?

• Chemistry is the study of the properties and behavior of matter.

• Matter has mass and occupies space.

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chemists do three things

(1) make new types of matter: materials,

substances, or combinations of substances with desired properties

(2) measure the properties of matter

(3) develop models that explain and/or predict the properties of matter.

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Classifications of Matter

• Matter is typically characterized by

(1) its physical state (gas, liquid, or solid)

(2) its composition (whether it is an element, a

compound, or a mixture).

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States of Matter

The three states of matter are

• Solid (s).

• Liquid (l).

• Gas (g).

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Classification of Matter Based on Composition

• A pure substance (usually referred to simply as a

substance) is matter that has distinct properties and a composition that does not vary from sample to

sample

• Elements (元素) are substances that cannot be decomposed into simpler substances.

• Compounds (化合物) are substances composed of

two or more elements; they contain two or more

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Molecular comparison of elements, compounds, and mixtures.

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Atom and Molecule

The elements hydrogen and oxygen themselves

exist naturally as diatomic (two atom) molecules:

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Compounds and Composition

• The Law of Constant Composition (or The Law of Definite Proportions) : Compounds have a definite composition. That means that the relative number of atoms of each element that makes up the compound is the same in any sample.

EX: Two samples of carbon dioxide are decomposed into their constituent elements. One sample produces 25.6 g of oxygen and 9.60 g of carbon, and the other produces 21.6 g of oxygen and 8.10 g of carbon. Show that these results are consistent with the law of definite proportions.

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Classification of Matter—

Mixtures

• Mixtures can vary in composition throughout a sample (heterogeneous) or can have the same composition throughout the sample (homogeneous).

• Ex:

Air is a homogeneous mixture of nitrogen, oxygen, and smaller amounts of other gases.

Salt, sugar, and many other substances dissolve in water to form homogeneous mixture

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Classification of Matter Based on Composition

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Properties of Matter

 Physical Properties can be observed without changing a substance into another substance.

 Some examples include boiling point, density, mass, or volume.

 Chemical Properties can only be observed when a substance is changed into another substance.

 Some examples include flammability, corrosiveness, or reactivity with acid.

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Types of Properties

 Intensive Properties are independent of the amount of the substance that is present.

Examples include density, boiling point, or color.

 Extensive Properties depend upon the amount of the substance present.

Examples include mass, volume, or energy.

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Physical and Chemical Changes

 Physical Changes are changes in matter that do not change the composition of a substance.

Examples include changes of state, temperature, and volume.

 Chemical Changes result in new substances.

Examples include combustion, oxidation, and decomposition.

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Separating Mixtures

 Mixtures can be separated based on physical properties of the components of the mixture. Some methods used are

filtration.

distillation.

chromatography.

Figure 1.12 Separation by filtration. A mixture of a 15 solid and a liquid is poured through filter paper. The liquid pass through the paper while the solid remains on the paper.

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Distillation

Distillation uses differences in the boiling points of substances to separate a

homogeneous mixture into its components.

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Chromatography

17 The differing abilities of substances to adhere to the surfaces

of solids can also be used to separate mixtures. This ability is the basis of chromatography

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The scientific method

Key characteristics of the

scientific method include

observation, formulation of

hypotheses, experimentation,

and formulation of laws and

theories.

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A Scientific Law (科學定律)

A brief statement that summarizes past observations and predicts future ones

• EX: “In a chemical reaction matter is neither created nor

destroyed.” --- Law of conservation of mass (質量守恆定律)

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SI Units

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Units of Measurement—

Metric System Prefixes

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Using SI Prefixes

• What is the name of the unit that equals (a) 10-9 gram, (b) 10-6 second, (c) 10-3 meter?

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Quiz

• One edge of a cube is measured and found to be 13 cm. The volume of the cube in m3 is _______

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Temperature

• The Kelvin (K) is the SI unit of temperature.

• The temperature is a measure of the average amount of kinetic energy of the atoms or molecules that compose the matter.

• Temperature also determines the direction of thermal energy transfer, or what we commonly call heat.

• Thermal energy transfers from hot to cold objects.

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Kelvin scale

• Kelvin scale (absolute scale) assigns 0 K (absolute zero) to the coldest temperature possible.

• Absolute zero (–273 °C or –459 °F) is the temperature at which molecular motion virtually stops. Lower temperatures do not exist.

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Temperature

• The Fahrenheit degree (oF) is five-ninths the size of a Celsius degree.

• The Celsius degree (oC) and the Kelvin degree (K) are the same size.

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Converting between Temperature Scales

• A weather forecaster predicts the temperature will reach 31 °C.

What is this temperature (a) in K, (b) in °F?

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Derived Units

• A derived unit is a combination of other units.

EX: the SI unit for speed is meters per second (m/s), a derived unit.

EX: Density has units that are derived from the units for mass and volume. (g/mL or g/cm3)

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exact numbers & inexact numbers

• Two kinds of numbers are encountered in scientific work: exact numbers (those whose values are known exactly) and inexact numbers (those whose values have some uncertainty).

 Exact numbers : there are 12 eggs in 1 dozen.

 Inexact (or measured) numbers : The balance measures to ±0.01 g.

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Accuracy versus Precision

• Accuracy (準確度) refers to how close the measured value is to the actual value.

• Precision (精密度) refers to how close a series of

measurements are to one another or how reproducible they are.

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The Reliability of a Measurement

Scientific measurements are reported so that every digit is certain except the last, which is estimated.

EX:

The first three digits are certain; the last digit is estimated.

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Significant Figures (有效數字)

• Significant figures deal with writing numbers to reflect precision (精密度).

• The precision of a measurement depends on the instrument used to make the measurement.

• The preservation of this precision during

calculations can be accomplished by using

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Significant Figures Rules

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Significant Figures Rules

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Exercise

• How many significant figures are in each number?

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Quiz:

• How many significant figures are in each number?

A) 0.00002510 B) 0.02500001 C) 250000001 D) 2.501 × 10-7 E) 2.5100000

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Significant Figures in Calculations

• Multiplication and Division Rule:

In multiplication or division, the result carries the same number of significant figures as the factor with the fewest significant figures.

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Exercise 1.8

• The width, length, and height of a small box are 15.5, 27.3, and 5.4 cm, respectively. Calculate the volume of the box, using the correct number of significant figures in your answer.

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Quiz

• 12.00000 × 0.9893

• 13.00335 × 0.0107

• (2.0560)(0.9391) / 12.006 = ________

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Significant Figures in Calculations

• Addition and Subtraction Rule:

In addition or subtraction the result carries the same number of decimal places as the quantity with the fewest decimal places.

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Quiz

• The correct result (indicating the proper number of significant figures) of the following addition is ________.

12+1.2+0.12+0.012=?

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Rounding in Multistep Calculations

• To avoid rounding errors in multistep calculations round only the final answer.

• Do not round intermediate steps. If you write down intermediate answers, keep track of

significant figures by underlining the least

significant digit.

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Exercise

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Quiz

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• A vessel containing a gas at 25 °C is weighed, emptied, and then reweighed as depicted in Figure 1.24. From the data provided, calculate the density of the gas at 25 °C

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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).

• We can set up a ratio of comparison for the equality either 1 in/2.54 cm or 2.54 cm/1 in.

• We use the ratio which allows us to change units (puts the units we have in the denominator to cancel).

Figure

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References

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