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
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
Compound
composed of 2 or more elements in a fixed ratio
properties differ from those of individual elements
EX: table salt (NaCl)
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