Chemistry Unit 1

Scientific Method

The process used to solve a problem

1. Identify a problem

2. Form a hypothesis – educated guess

3. Design Experiment

4. Perform experiment

5. Analyze data

6. Draw Conclusion and communicate the results/summarize data

7. If you have a flawed experiment, modify the experiment and go back to #4 before reaching conclusion


Significant Figures

Digits that carry meaning contributing to its precision.

ex.) .00010 = 2 sig figs; 630. = 3 sig figs; 806 = 3 sig figs; 700 = 1 sig fig; 4.200 = 4 sig figs; 9.0 x 103 = 2 sig figs


Scientific Notation

A way of writing numbers that are too big or too small to be conveniently written in decimal form.

Ex.) 405,000,000: 4.05 X 108

.0000120: 1.2 x 10-5

8.85 x 104: 88500

4.953 x 10-2: .04953


Factor Label Method

A method that helps to convert from 1 unit to another


Reasons why any measurement may be uncertain:

1.) Precision (human error)

2.) Accuracy (beaker vs. graduated cylinder)

1.) being consistent and reproducible (getting close to the same answer over and over)

When adding or subtracting (#’s with decimals) round the numbers being added or subtracted to the least precise measurement (the number with the least amount of decimal places) before getting answer.

ex.) 7.102 + 17.75 =; 7.10 + 17.75 = 94.85

When multiplying or dividing, round the answer to the least precise number in the problem.

ex.)5.00 x 4.135 = 20.675 round to least precise number=; 20.68!!

2.) hitting the targeted value consistently


Density (g/ml)

Density = mass(g)/volume(ml)

or

D= m/v


Chemistry

the study of the composition, structure and properties of matter and the changes it undergoes


chemical

a substance that has a definite composition


Matter

anything that has mass and occupies space


Mixtures:

1.) heterogeneous

2.) homogeneous -solution

blend of 2 or more kinds of materials, each of which retains their own identity

1.) mixtures that are not the same throughout

ex.) salad, dirt

2.)mixtures that have the same composition throughout ex.) saltwater, atmosphere


Pure Substance

homogeneous MATERIAL which has a fixed composition throughout

ex.) ELEMENT cannot be decomposed by normal chemical means (found on periodic table – gold, hydrogen) or COMPOUND can be decomposed by normal chemical means (combined elements that can only be broken by a chemical reaction – water, sodium chloride)


Atom

smallest unit of an element that maintains the properties of that element


Element

a pure substance made of only one atom (includes diatomic atoms such as N2, H2, etc)


Compound

a substance that is made from the atom of 2 or more different elements that are chemically bonded/combined.


Properties

1.)Extensive

2.)Intensive

used to distinguish between substances. It may be a characteristic that defines a group of substances. They also help to reveal the identity of unknown substances. 1.) depend on the amount of matter present

(ex. volume, mass, length)

2.)do not depend on the amount of matter

(ex. melting/boiling points, density, color)


1.)Physical Property

a.)Physical Change

b.)Change of State

1.) characteristic that can be observed or measured without changing the identity of the substance (ex. melting/boiling points, density, color)

a.) a change in substance that does not involve a change in the identity of the substance (ex. cutting, dissolving, ice melting)

b.) physical change of a substance from one state to another (ex. melting, boiling, freezing)


States of Matter:

1.) Solid

2.) Liquid

3.) Gas

1.)has definite volume and shape; particles are packed together

2.)has definite volume but indefinite shape; particles are close together, but they can move

3.) has neither definite shape of volume; particles can move faster and are further apart from one another


Examples of Physical Properties

1.)Viscosity: resistance to flowing

2.)Conductivity: ability to allow heat flow

3.)Malleability: ability of a solid to bend

4.)Hardness: ability to scratch another substance 5.)Melting Point: temperature at which a substance changes from a solid to a liquid

6.)Boiling Point: temperature at which a substance changes from a liquid to a gas

7.)Density: measure of the “heaviness” of an object; mass per volume


1.)Chemical Property

2.)Chemical Change

1.)a substance’s ability to undergo a change that transforms a substance into different substances

2.)a change in which one or more substances are converted into different substances with different properties

ex.)when charcoal(carbon) burns, it combines with oxygen in the air to become carbon dioxide gas (CO2) or when milk sours


Examples of Chemical Properties

1.)Flammability: ability to burn in the presence of oxygen 2.)Reactivity: how readily a substance combines chemically with another substance


Chemical Change Indicators

1.)Change in color – copper turns green in the presence of moist air

2.)Absorption/Release of Heat

-Endothermic: absorbing/gaining heat =>substance feels cold

-Exothermic: releasing/losing heat =>substance feels hot

3.)Production of a gas – vinegar and baking soda give off CO2 gas

4.)Formation of a precipitate – a solid forming when 2 liquids are added together