Chapters 1 & 3

Chemistry- A Study of the Properties and Changes of Matter

Science vs. Chemistry

Science- "knowledge attained through study or practice“ (Webster’s)

Translation: Systematic approach to determine the nature of the universe

Chemistry- “the study of the composition and changes undergone by materials”

Translation: Using the scientific method to figure out what stuff is and what it can do

Chemistry Can Be…

Pure For the advancement

of knowledge about our world

Applied For a specific issue

that faces society

Pharmaceuticals, etc.

Scientific Method Question Hypothesis Experiment Results Conclusion Peer review

Maybe, much, much later…

Theory

Question

After making observations of a phenomenon Generate a SPECIFIC question to investigate

EX: Why do apples turn brown if left out?

Hypothesis

After RESEARCH ….is an EXPLANATION of the observations Followed by a specific prediction based on

past experimental results or research Usually in the IF…, THEN… format EX: Browning of apples is caused by heat Prediction: If apples are allowed to reach a

temperature of 20 degrees Celsius, then browning will occur

Variables

Independent variable: controlled by experimenter

If results are graphed, independent variable goes on the x axis (time is usually independent)

Dependent variable: depends on independent variable

If graphed, results go on y axis

Experiment

Designed to INVESTIGATE THE HYPOTHESIS

EX: 10 apples are kept below 20 C

10 apples at 20 C

10 apples above 20 C

Results/Data Analysis

Compile and LOOK FOR PATTERNS in experimental results

Experimental results confirm or contradict predictions made on the basis of a hypothetical explanation

EX: 0 apples browned below 20 C, but 50% of apples above 20 C started browning within 24 hours

Conclusion

Addresses whether or not the results SUPPORT or REFUTE the HYPOTHESIS

Errors and future research are offered here

EX: The results show some support for the hypothesis in that half of the apples kept above 20 C did brown. However, …

Peer Review

After SEVERAL TRIALS and repeatable results

Publish experiment in a scientific journal after peer review

Theory

A theory is a well-supported hypothesis Formulated after EXTENSIVE, DIVERSE,

AND RELIABLE data exists to support an explanation of a phenomenon

Requires many years of research and support from many fields

Important Distinctions

Qualitative- sensory observations (EX: brown) Quantitative- numerical measurements (EX: 5 lbs) Theory- Explains why for a given phenomenon Law- Describes a given phenomenon

The Law of Gravity is that what goes up must come down.

A Theory of Gravity would explain why this happens Observation- objective description of phenomena Inference- subjective explanation of phenomena

Matter Classification

Matter Flowchart

Pure Substances

Mixtures

A. Matter Flowchart

MATTER

Can it be physically separated?

Homogeneous Mixture

(solution)

Heterogeneous Mixture Compound Element

MIXTURE PURE SUBSTANCE

yes no

Can it be chemically decomposed?

noyesIs the composition uniform?

noyes

Colloids Suspensions

A. Matter Flowchart

Examples:

graphite

pepper

sugar (sucrose)

paint

soda

element

hetero. mixture

compound

hetero. mixture

solution

B. Pure Substances

Element composed of identical atoms EX: copper wire, aluminum foil

B. Pure Substances

Compound

composed of 2 or more elements in a fixed ratio

properties differ from those of individual elements

EX: table salt (NaCl)

B. Pure Substances

For example…

Two different compounds, each has a definite composition.

C. Mixtures

Variable combination of 2 or more pure substances.

Heterogeneous Homogeneous

Tyndall Effect

Disperses Light

C. Mixtures

Solution homogeneous very small particles no Tyndall effect Tyndall Effect

particles don’t settle EX: rubbing alcohol

C. Mixtures

Colloid heterogeneous medium-sized particles Tyndall effect particles don’t settle EX: milk

C. Mixtures

Suspension heterogeneous large particles Tyndall effect particles settle EX: fresh-squeezed

lemonade

C. Mixtures

Examples:

mayonnaise

muddy water

fog

saltwater

Italian salad dressing

colloid

suspension

colloid

solution

suspension

More Important Distinctions

Intensive/extensive Material- specific type of matter Matter- has mass and takes up space (has property

of inertia) Mass- amount of stuff in an object Weight- force of gravity of mass

Mixture- composed of 2 or more substances physically combined

Physical change- occurs without altering makeup Chemical change- occurs through alteration of substance

Substance- purely 1 type of matter

Separating Mixtures

ALL MIXTURES CAN BE SEPARATED PHYSICALLY Filtration- used to separate a mixture with widely

varying particle size EX: rocks and water

Distillation- used to separate a liquid mixture EX: alcohol and water

Crystallization- used to purify a solid EX: impure aspirin can be dissolved and recrystallized

from an alcohol/water solution Chromatography- separates a mixture based on

polarity (affinity for stationary/mobile phase)

Substances

Compounds can only be formed or broken down by chemical reactions Law of Conservation of Mass- mass can be neither be

created nor destroyed in a chemical reaction Matter CAN change state

SOLID LIQUID GAS

Definite Shape

YES NO NO

Definite Volume

YES YES NO

Particle Spacing

CLOSE CLOSE WIDE

Laws of Compounds

Law of Definite Proportions Ratio of elements in a

compound is constant

EX: H2O is always 16g of O for every 2g of H

Percent by Mass %mass = (mass element/mass compound) *100

%O in H2O = (16g/18g)* 100 = 88.9%

Law of Multiple Proportions If two compounds can

result from the same element, the ratio will be in small whole numbers

EX: H2O vs H2O2

Chemical and Physical changes

A chemical change results in the formation of new stuff. Burning Rusting/Corrosion Decomposition

A physical change does not make new stuff. Melting/freezing/boiling Crushing Dissolving

The Periodic Table of Elements

Elements are arranged by increasing atomic number

Groups- vertical columns in the table that share chemical properties

Periods- horizontal rows in the table that share the same principal energy level