observations ◦ existing knowledge – ask a question ◦ do some background research ◦...
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Observations◦ Existing knowledge – ask a question◦ Do some background research◦ Qualitative data – information that describes color,
odor, shape or some other physical characteristic.◦ Quantitative data – numerical information; tells you
how much, how little, how big, how tall, how fast, etc.
Hypothesis◦ Testable statement or prediction◦ A proposed explanation for an observation
The systematic approach
Experiment◦ A set of controlled observations that test the
hypothesis◦ Need data to support a hypothesis◦ Independent Variable – variable that you change.◦ Dependent Variable – variable that changes in
response to the independent variable.◦ Control – a standard for comparison◦ Produces data◦ May need to go back and revise hypothesis and
start experiment over.
Continued…
Data - Analysis◦ Collected from the experiment and organized, typically
in a chart or table.◦ Used to draw conclusions
Conclusion◦ A judgment based on the information obtained◦ Hypothesis can never be proven, so data is always said
to “support hypothesis”◦ If data does not support, hypothesis is discarded or
modified◦ Most hypotheses are not supported but yield new
information◦ Model – a visual, verbal and/or mathematical
explanation of experimental data
Continued…
Experiments may lead to information that can be reproduced over and over
Theory – an explanation that has been supported by many, many experiments.◦ States a broad principle of nature that has been
supported over time◦ Still subject to new experimental data and can be
modified i.e. Einstein’s Theory of Relativity
Theory vs. Law
Law – A relationship in nature that is supported by many experiments.◦ Same conclusion reached over and over, without
exception◦ It is up to scientists to conduct experiments to
explain why these exist i.e. Newton’s Law’s
Anything that has mass and takes up space
Mass – a measurement that reflects the amount of matter
Weight – a measure of the amount of matter and the effect of Earth’s gravitational pull on that matter.
Matter
Solid – matter with its own definite shape and volume◦ Ex: wood, iron, paper, sugar
Liquid – matter that flows◦ Ex: water, blood, mercury
Gas – matter that flows to conform to the shape of its container and fills the entire volume◦ Neon, methane, air
States of Matter
States of Matter
State Shape Volume Compressible?
Solid Definite Definite No
Liquid Indefinite Definite No
Gas Indefinite Indefinite Yes
A characteristic that can be observed or measured without changing the samples composition.◦ Density◦ Color◦ Odor◦ Taste◦ Hardness◦ Melting point◦ Boiling point◦ Solubility
Physical Properties
Extensive Properties◦ Depends of how much (the extent) matter there is◦ Ex: mass, length, volume
Intensive Properties◦ Independent (does NOT depend) of how much
matter◦ Substance can often be identified by intensive
property◦ Ex: density, temperature
Water boils at 100oC
There are 50 lbs of sand in a bucket.
Oil is less dense than water.
A piece of copper is 10m long.
Identify the following as either intensive or extensive
intensive
intensive
extensive
extensive
The ability of a substance to combine with or change into one or more other substances◦ Combustibility
Sodium reacts with water, may combust◦ Reactivity with other substances
Iron rusts when exposed to oxygen
Chemical Properties
Substance (Pure Substance)◦ Matter that has uniform and unchanging
composition◦ Only 1 type of matter present
Element◦ A pure substance that cannot be separated into
simpler substances by physical or chemical means Compound
◦ Combination of two or more different elements chemically combined
Mixture◦ Combination of two or more pure substances in
which each pure substances retains its chemical properties
Types of Matter
Sulfur dioxide
Brass (Zn + Cu)
Fluorine
Lemonade w/ pulp
Gasoline
Beach sand
Classify as either Pure Substance or Mixture, then as element, compound, heterogeneous or homogenous.
Pure substance, compound
Mixture, homogenous
Pure substance, element
Mixture, heterogeneous
Mixture, homogenous
Mixture, heterogeneous
Homogeneous Mixture-◦ Has a constant composition throughout◦ Single phase◦ Looks the same throughout◦ Also referred to as solutions
Heterogeneous Mixture-◦ Does not blend smoothly throughout◦ Individual substances remain distinct
Mixtures
Metals – ◦ Have luster (shine)◦ Malleable (not brittle)◦ Ductile (can be drawn into wires)◦ Conduct heat and electricity
Nonmetals – ◦ Brittle◦ Poor conductors of heat and electricity
Metalloids – ◦ Have characteristics of both metals and
nonmetals
General Classes of Elements
A homogeneous mixture Composed of 2 parts
◦ Solvent – substance there is more of Dissolving substance
◦ Solute – substance that is added to solvent Dissolved substance
Solutions
Alter a substance without changing its composition
Identifying properties remain unchanged◦ Phase change◦ Breaking or cutting◦ Dissolving◦ Bend◦ Crumple◦ Split◦ Crush
Physical Changes
One or more substances changing into new substances
Different substances formed◦ Burning◦ Rusting◦ Decaying or spoiling◦ Fermentation◦ Acid reacting with metal
Chemical Changes
Heat gained or lost
Production of a gas
Formation of a precipitate
Color change
Signs of a Chemical Change
Mass is neither created nor destroyed during a chemical reaction, it is always conserved.
Mass of reactants always equals mass of products.
Massreactants = Massproducts
Law of Conservation of Mass
Regardless of amount, a compound is always composed of the same elements in the same proportion by mass.◦ Water, H2O ◦ Always made of 2:H’s and 1:O no matter how
much water you have
Law of Definite Proportions
When different compounds are formed by a combination of the same elements, different masses of one element combine with the same relative mass of the other element in a ratio of small whole numbers.
H2O vs. H2O2
Water has 2 H’s for every 1 O Hydrogen peroxide has 2 H’s for every 2 O’s
Law of Multiple Proportions
Use different properties of substances to separate them◦ Sand and iron filings◦ Sand and salt◦ Sand and water◦ Water and salt water◦ Oil in water (immiscible liquids)◦ Mixture of pigments
Methods of Separating Mixtures
Remove iron with magnet
Add water, dissolve salt, filter sand, evaporate water filter
Distill the water
Settle and extract less dense liquid
Paper chromatography
Defined unit in a system of measurement that is based on an object or event in the physical world.
Independent of other units.
Base Units
Quantity Base UnitTime Second (s)
Length Meter (m)
Mass Kilogram (kg)
Temperature Kelvin (K)
Amount of a Substance Mole (mol)
Electric Current Ampere (A)
Luminous Intensity Candela (cd)
Base Units
Unit that is defined by a combination of base units.◦ Volume – the space occupied by an object.
derived unit – m3
cm3 = mL◦ Density – ratio that compares mass of an object to
its volume.
Derived Units
3cm
gor
mL
g
How can we rearrange this equation if we have the density and volume.
Density
volume
massdensity
massvolumedensity
Kelvin scale, founded by William Thompson who was known as Lord Kelvin.◦ Water freezes at 273 K◦ It boils at 373K◦ The scale is the same as Celsius, just different
temperature points Celsius + 273 = Kelvin
Kelvin – 273 = Celsius
Temperature
If the density of an object is 2.70 g/cm3 and the mass of the object is 1.65g, what is the volume of the sample?
Problems
v
mD
D
mv
370.2
65.1
cmgg
v 3611.0 cmv
An object has a density of 7.7g/cm3 and a volume of 5 mL, what is the density of the object?
Problem
v
mD m = v x D
m = 5 cm3 x 7.7g/cm3 = 39 g
Convert the following:◦ 357oC to Kelvin
357oC + 273 = 630K
◦ -39oC to Kelvin -39oC + 273 = 234K
◦ 266K to Celsius 266K – 273 = -7oC
◦ 332K to Celsius 332K – 273 = 59oC
Problem
Precision◦ The agreement between measurements.◦ How close a set of measurements are to each
other.
Accuracy◦ The nearness of a measurement to its actual
value.◦ How close you are to the true value.
Precision vs. Accuracy