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Chemistry

The study of

1. Matter

2. Properties of matter.

3.Changes that matter undergoes.

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Scientific Method

A systematic approach to solving problems.

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Qualitative Observation

• An observation that does not involve any numerical information.– Carbon monoxide is a poisonous gas– Soap is slippery– Gold does not rust– Aluminum has a low density– Tin is a shiny, gray metal

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Quantitative Observation

• An observation involving numerical values in a measurement.– Carbon dioxide freezes at -78ºC– The density of aluminum is 2.70 grams/mL– The sample of gold weighs 34.6 grams– The chemical reactions liberates 45.5 calories

of energy

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Matter

Anything that has mass and takes up space.

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Matter

• Atoms are the building blocks of matter.

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Matter

• Atoms are the building blocks of matter.• Each element is made of the same kind of atom.

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Matter

• Atoms are the building blocks of matter.• Each element is made of the same kind of atom.• A compound is made of two or more different kinds

of elements.

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Classification of Matter

• Elements (Pure)

• Compounds (Pure)

• Mixtures (Impure)

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Elements

• Elements are the simplest form of matter that can exist under conditions that we normally encounter in the laboratory

• An element is a substance that cannot be separated into simpler substances by chemical methods.

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Elements

• 113 Elements have been identified.

• 82 Elements occur naturally on Earth– Gold, Aluminum, Lead, Oxygen, Carbon

• 31 Elements have been created by scientists.– Technetium, americium, seaborgium

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Elements

• Elements can exist in either the atomic or molecular forms.– Neon Ne

– Hydrogen H2

– Bromine Br2

– Phosphorus P4

– Sulfur S8

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States of Matter

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Compound

A compound is a substance composed of atoms of two or more elements chemically combined in fixed proportions (by either mass or atoms).

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Compounds

• A compound does not change its identify in physical changes but can be broken down into its constituent elements by chemical methods.

• The simplest unit of a compoud is the molecule or ion-pair.

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Carbon Dioxide

• 44.01 grams of carbon dioxide contains 12.01 grams of carbon and 32.00 grams of oxygen. (2.66 : 1.00 ratio of oxygen to carbon).

• 1 molecule of carbon dioxide contains 1 atom of carbon and two atoms of oxygen.

• Carbon dioxide contains 27.29% carbon and 72.71% oxygen (by mass).

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Compounds

• Carbon dioxide CO2

• Magnesium oxide MgO

• Sodium Phosphate Na3PO4

• Sucrose C12H22O11

• Penicillin C14H21N3O6S

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Mixtures

• Mixture – A combination of two or more substance in which the substances retain their distinct identities.– Seawater– Sand in water– Coca-Cola– Bronze alloy– Atmospheric gases– Italian salad dressing

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Characteristics of Mixtures

• Variable composition.

• Variable physical properties.

• Separated into their components by physical methods.– Boiling– Filtration– Decanting

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Homogenous vs. Heterogeneous

• Homogeneous – Uniform throughout sample; no boundaries and separate phases.

• Heterogeneous – Non-uniform throughout sample; boundaries and multiple phases are present.

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Classification of Matter

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Classification of Matter

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Mixtures and Compounds

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Properties of Matter

• Intensive Properties:□ Independent of the amount of the

substance that is present.• Density, boiling point, color, etc.

• Extensive Properties:□ Dependent upon the amount of the

substance present.• Mass, volume, energy, etc.

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Properties of Matter

• Physical Properties

• Chemical Properties

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Physical Properties

• Physical Properties:□ Can be observed without changing a substance

into another substance.• Physical state (gas, liquid, solid) • Mass• Volume• Color/Luster• Hardness• Boiling point • Melting point• Density

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Chemical Properties

• Chemical Properties:□ Can only be observed when a substance is

changed into another substance.• Flammability or combustibility • Corrosiveness• Reactivity with acid, etc.

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Changes of Matter

• Physical Changes:□ Changes in matter that do not change the

composition of a substance.• Changes of state, temperature, volume, etc.• Freezing• Boiling• Melting• Condensation• Sublimation• Dissolving sugar in water`

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Chemical Changes

• Chemical Changes:□ A change in which one or more kinds of

matter is transformed into a new kind of matter or several new kinds of matter.

□ Changes that result in new substances.□ Chemical composition is altered.

• Combustion • Oxidation • Decomposition etc.

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Chemical Reactions

In the course of a chemical reaction, the reacting substances are converted to new substances.

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Chemical Reactions

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Compounds

Compounds can be broken down into more elemental particles.

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Electrolysis of Water

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Example of Chemical Change

• Magnesium metal combusts to produce the white ash, magnesium oxide.

2 Mg(s) + O2(g) → 2 MgO(s)

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Example of Chemical Change

• Sodium reacts vigorously with water to produce hydrogen gas and an aqueous solution of sodium hydroxide.

2 Na(s) + 2 H2O(l) → H2(g) + 2 NaOH(aq)

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Separation of Mixtures

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Distillation:

Separates homogeneous mixture on the basis of differences in boiling point.

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Distillation

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Filtration:

Separates solid substances from liquids and solutions.

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Chromatography:

Separates substances on the basis of differences in solubility in a solvent.

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Measurements

• Numerical Value

• Uncertainty

• Units

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Significant Figures

• When physical quantities are used in arithmetic, it is important that the number of digits reported represents the uncertainty in the original measurements.

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Significant Figures

• Rule #1: Any digit that is not zero is significant.

• 12.345 grams

• Rule #2: Zeros between nonzero digits are significant.

• 20.05 mL

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Significant Figures

• Rule #3: Zeros to the left of the first nonzero digit are not significant.

• 0.0125 kg

• Rule #4: If a measured number is greater than “1”, then all zeros to the right of the decimal point are significant.

• 2.500 meters

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Significant Figures

• Rule #5: If a number is less than “1”, then only the zeros that are at the end of the number and in the middle of nonzero digits are significant.

• 0.2500 grams

• 0.06050 tons

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Significant Figures - Multiplication or Division

• The number of significant figures in the result of multiplication or division is set by the original number that has the smallest number of significant figures.

• 4.51 x 3.6666 = 16.536366

• 16.5

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Significant Figures

0.0608 x 1025.40

25.06

= 2.487802075

2.49

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Significant Figures - Addition or Subtraction

• The answer cannot have more digits to the right of the decimal point than any of the original numbers possess.

• 89.332 + 1.1 = 90.432

• 90.4

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Exact Numbers

• Numbers from definitions or numbers of objects are considered to have an infinite number of significant figures.

(i.e. conversion factors, counting numbers• The average of three measured lengths: 7.65

m, 7.49 m, and 7.60 m.• (7.65 + 7.49 + 7.60)/3 =

• 7.58 not 8

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Uncertainty in Measurements

Different measuring devices have different uses and different degrees of accuracy.

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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.

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SI Units

• Système International d’Unités• Uses a different base unit for each quantity

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Metric System

Prefixes convert the base units into units that are appropriate for the item being measured.

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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.

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Conversion Factors

• Length --- 1 meter = 39.37 inches

• Mass --- 453.6 grams = 1 pound

• Volume --- 1 liter = 1.056 quarts

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Dimensional Analysis Method of Solving Problem

• Determine which unit conversion factor(s) are required.

• Carry units through calculation.

• If all units cancel except for the desired unit(s), then the problem was solved correctly.

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Temperature

A measure of the average kinetic energy of the particles in a sample.

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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.

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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

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Temperature

• The Fahrenheit scale is not used in scientific measurements.

F = 9/5(C) + 32 C = 5/9(F − 32)

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Density

Physical property of a substance

d=mV