Test 1 Review

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

Classes of Matter

Matter

Pure substance mixture

element homogeneouscompound 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

Precision vs. Accuracy

You analyze a sample of copper sulfate and find that it is 68% copper. The theoretical value of copper is 80%. What is the percent error?

Example

10080

6880%15