Chemistry 101 : Chap. 1Chemistry 101 : Chap. 1

Matter and Measurement

(1) What is Chemistry and Why we study it

(2) Classification of Matter

(3) Properties of Matter

(4) Units of Measurement

(5) Uncertainty in Measurement

(6) Dimensional Analysis

The Study of ChemistryThe Study of Chemistry

Chemistry: The study of the properties of matter and the

changes that matter undergoes.

Matter : Physical material of the universe

Anything that has mass and occupies space

Changes in Matter : Physical or Chemical changes

Why Chemistry?

Chemistry is the central science

Chemistry is a practical science and has profound

impact on our daily living

Macroscopic vs. MicroscopicMacroscopic vs. Microscopic

Macroscopic World : Realm of ordinary-sized object.

Things we can see with the naked eye.

(Sub)Microscopic World : Realm of atoms and molecules

Carbon nanotube (10-9 m)

Chemistry is the science that seeks to understand the propertiesand behavior of matter (macroscopic) by studying the propertiesand behaviors of atoms and molecules (microscopic)

Major Divisions in ChemistryMajor Divisions in Chemistry

Physical Chemistry (CHM321, CHM420)

Organic Chemistry (CHM211, CHM212)

Inorganic Chemistry (CHM 455, CHM546)

Analytical Chemistry (CHM235, CHM435)

Biochemistry (CHM365, CHM568)

All divisions are interrelated and cannot bestanding alone.

Classification of Matter: pure substance vs. mixture

Classification of Matter: pure substance vs. mixture

Pure Substance: A sample of matter that has distinct properties and a composition that doesn’t vary from sample to sample (either element or compound)

Elements: A pure substance that cannot be decomposed into simpler substances. The basic unit of an element is an atom.

Argon gas (atoms) Nitrogen gas (molecules)

Nitrogen molecules

Nitrogen atom

Classification of Matter: pure substance vs. mixture

Classification of Matter: pure substance vs. mixture

Compound : Substances that are composed of two or more elements. The basic unit of compound is a molecule

ammonium (molecule)

Mixture : Combinations of two or more substances in which each substance retains its own chemical identity.

Two or more elements(compound)

Two or more substances(mixture)

nitrogen atom

hydrogen atom

ElementsElements

At the present time, there are 116 elements

Periodic Table of the Elements

= H2, N2, O2, F2, Cl2, Br2, I2

ElementsElements

Not all elements are equal…

CompoundsCompounds

Most elements can interact (or react) with other elements

to form compounds

Example: Combine hydrogen & oxygen to generate water

Oxygen Hydrogen water

However, elemental hydrogen and oxygen exist as diatomicmolecules (H2 and O2) in nature.

+

O2 + 2H22H2O

MixtureMixture

Components: The substances making up a mixture

Homogeneous Mixture (solution) : Uniformly distributed throughout. (air, salt solution, sugar solution …)

Heterogeneous Mixture : Do not have the same composition, properties and appearance throughout. (rock, wood …)

Air Oil on water

Classification of MatterClassification of Matter

Classification of MatterClassification of Matter

(1) 14 K gold

(2) Orange Juice

(3) A cup of coffee

(4) Mud

Example

Separation of MixtureSeparation of Mixture

Separate a mixture into its components by taking advantage

of the difference in their properties

Filtration : Separation is based

on the size of particles in the

mixture. Filtration is used with

heterogeneous mixtures

Separation of MixtureSeparation of Mixture

Distillation : Separation is based

on the boiling points of the

components in the mixture.

Distillation is typically used

with homogeneous solutions.

Water changes itsstates from gas toliquid

Separation of MixtureSeparation of Mixture

Chromatography : Separation is based on the solubilities

of the components in the mixture. It is normally used with

homogeneous mixture.

Paper chromatography

Classification of Matter: states of matter

Classification of Matter: states of matter

States of matter: A sample of matter can have three physically different states

Gas : Indefinite volume and indefinite shape

(depends on the volume and shape of its container)

Liquid : definite volume, but indefinite shape.

Solid : definite volume and definite shape

Pure substance can have any state dependingon the temperature and pressure

Three States of WaterThree States of Water

Properties of MatterProperties of Matter

Physical properties : They can be measured without

changing the identity and composition of the substance

Ex. color, order, density, boiling point…

Chemical properties : They describe the way a substance

can change or react

Ex. flammability, solubility, …

Physical vs. Chemical PropertiesPhysical vs. Chemical Properties

silver-grey metal

melting point: 420oC

generates hydrogen when dissolved in sulfuric acid

density (25oC) = 7.13 g/cm3

reacts with oxygen to form Zinc oxide (ZnO)

Example : Zinc (Zn)

Properties of MatterProperties of Matter

Extensive properties : Properties that depend on the quantity of a sample.

Ex. Volume : + = V1 + V2 = V1 + V2

Intensive properties : Properties that are independenton the quantity of a sample

Ex. Temperature : + = T T T

Extensive vs. Intensive PropertiesExtensive vs. Intensive Properties

Boiling/melting point (bp/mp)

Mass

Density

Pressure

Example :

Changes of MatterChanges of Matter

Physical changes :

Phase changes, but it is

still H2O (no change in its

composition)

Chemical changes :

Aluminum (Al) reacts with

Bromine (Br2). (A substance

is transformed into a chemically

different substance: AlBr3)

Units of Measurement : SI UnitUnits of Measurement : SI Unit

Système International (SI) d’Unités

International agreement on the metric units for the

uses in science (1960)

Units of Measurement : PrefixesUnits of Measurement : Prefixes

Prefixes : They are used to indicate decimal fractions

or multiples of various units.

A Megabyte of memory : 106 bytes of memoryFemtochemistry : chemistry that occurs on the time scale of 10-15 second check out http://www.lms.caltech.edu (prof. Zewail’s homepage)

Length and MassLength and Mass

Length : 1 meter (m) = 100 cm Mass : 1 kilogram (kg) = 1000 g

Metric to English conversion

1 m = 1.093613 yard

1 cm = 0.393701 inch

1 kg = 2.204623 lb

Check out http://www.digitaldutch.com/unitconverter/

NOTE: Mass and weight are not the same thing. Mass is an intrinsic property of matter, but weight depends on the gravity.

TemperatureTemperature

Water freezing Water boiling

Celsius scale (oC) 0 100

Fahrenheit scale (oF) 32 212

Kelvin : K = oC + 273.15 (exact)

Absolute zero temperature : 0 K = 273.15 oC

The lowest attainable temperature in our universe

oC = 5/9 (oF 32) oF = 9/5(oC) + 32

TemperatureTemperature

(98.6 oF 32)5/9 = 37 oC

37 oC + 273.15 = 310.15 K

William Thomson Kelvin(1824-1907)

“On an Absolute Thermometric Scale” Philosophical Magazine, vol. 1 pp. 100-106 (1848)

Derived UnitsDerived Units

Use the defining equation for the quantity of interest

and substitute the appropriate SI units

Volume: abc = (length)3 = m3

In chemistry, we normally usesmaller units.

(1) Liter : (10 cm)3 = 1 L = 1 dm3 = 10-3 m3

1 gal = 3.8 L

(2) Milliliter = 1 mL = 10-3 L = 1 cm3 = 1 cc

ab c

Derived UnitsDerived Units

Density : The amount of mass in a unit volume of substance

3m

kg

volume

massdensity SI unit of

density

In chemistry, we typically use g/mL = g/cm3 = g/cc

Density depends on temperature

Don’t be confused about density and weight

Density, Volume and MassDensity, Volume and Mass

(1) 1.00 102 g of mercury occupies a volume of 7.36 cm3. What is the density of mercury?

(2) The density of liquid methanol is 0.791 g/mL. What is the volume of 65.0 g of liquid methanol?

(3) The density of gold is 19.32 g/cm3. What is the mass in gram of a cube of gold if the length of the cube is 2.00 cm?

Uncertainty in MeasurementUncertainty in Measurement

We need to distinguish two different types ofnumber in science

Exact Number : Defined number 1 dozen = 12, 1 m = 100 cm Counted number There are 120 students in the class.

Inexact Number : Numbers from measurement (human errors, machine errors..)

Precision and AccuracyPrecision and Accuracy

Precision : How closely individual measurements agree with one another.

Accuracy : How closely individual measurements agree with the correct or “true” value.

good precisionpoor accuracy

good precisiongood accuracy

poor precisionpoor accuracy

Significant FiguresSignificant Figures

(1) Measured quantities are generally reported in such a

way that only the last digit is uncertain.

mass of a dime = 2.2405 g

Uncertain. Could be 6 or 4…

(2) Sometimes, sign is used to specify the uncertainty.

mass of a dime = 2.2305 0.0002 g

Significant Figures : All digits of a measured quantity,

including the uncertain one.

2.2405 g 5 significant figures

Rules for Significant FiguresRules for Significant Figures

(1) All non-zero digits are significant

(2) Zeros at the beginning of a number are never significant count the digits starting with the first non-zero digit 0.0026 has TWO significant figures

(3) Zeros between non-zero digits are significant 0.00206 has THREE significant figures

(4) Zeros at the end of a number are significant. 0.002060 has FOUR significant figures 2060 has FOUR significant figures

2.06 x 103 has THREE significant figures

Significant Figures in CalculationSignificant Figures in Calculation

The number with the fewest number of significant figureslimits the certainty of the calculated quantity.

Multiplication & Division : The final answer can have

no more significant figures than the fewest number of

significant figures in any number in the problem.

Addition & Subtraction : The final answer can have

no more decimal places than the fewest number of

decimal places in any number in the problem

Significant Figures in CalculationSignificant Figures in Calculation

Example 1: Area of a rectangle whose measured edge lengths are 6.221 cm and 5.2 cm

Area = (6.221 cm) x (5.2 cm) = 32.3492 cm2 =

Only 2 significantfigures

Include only 2 significant figures

Example 2 : Addition of three measured numbers

20.42 1.322+ 83.1

104.842

Significant Figures in CalculationSignificant Figures in Calculation

When calculation involves multiple steps…

Retain at least one more extra digit (past the number

of significant figure) in each step

When you use a calculator…

Enter the numbers one after another (without

worrying about significant figures) and rounding

only the final answer

Significant Figures in CalculationSignificant Figures in Calculation

Example 3: 863 [1255 (3.45 108)]

= 863 [1255 372.6]

= 863 882.4

= 761511.2

=

Example 4: (0.0045 20000.0) + (2813 12)

= 90.0 + 33800

= 33890

=

From calculator = 33846 =

Dimensional AnalysisDimensional Analysis

We carry units through all calculations. Units behave

like numbers: they are multiplied together, divided

into each other, or canceled.

Advantages of dimensional analysis

(1) It ensures that your answer has the correct unit

(2) It makes it easier to find out possible errors

Example: How many inches are in 10 cm?

in. 93701.3cm 1

in. 0.393701 cm 10 in./cm 4000.25

in. 0.393701

cm 1 cm 10 2

Correct Wrong

Unit ConversionUnit Conversion

unit desiredunitgiven

unit desired unit given

Conversion factor

Example: The speed of N2 in air at 25 oC is 515 m/s. Convert the speed into mile/hour

Unit ConversionUnit Conversion

Example: The density of water is 1.00 g/mL.

What is the mass 1.00 gal of water in grams?

An exampleAn example

The density of gold is 19.32 g/cm3. If 2.00 g of gold wire has 0.12 mm

radius, how long the wire is?