What is Chemistry

The science that deals with matter, and the changes that matter

undergoes.

Physical Change• Physical state is altered, but composition is the

same.• SOLID LIQUID Melting• LIQUID GAS Boiling• GAS LIQUID Condensing• SOLID GAS Sublimation• GAS SOLID Reverse

sublimation or deposition

• LIQUID SOLID Freezing

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Physical Change: the composition of the substance remains the same but the state changes.

Physical Properties

• Color• Odor• Density• Hardness• Solubility• Melting Point• Boiling Point

Chemical Change

• Exhibited when a substance reacts with other substances

• Atoms are rearranged to form a new substance

• Often observable such as color change or change in energy

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Chemical Change: a new substance is formed.

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An extensive property of a material depends upon how much matter is is being considered.

An intensive property of a material does not depend upon how much matter is is being considered.

• mass

• length

• volume

• density

• malleability

• color

Extensive and Intensive Properties

1.6

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Elements and the Periodic Table

• Each element is represented by a name and a symbol. (Periods/groups - alkali metals, alkaline earth metals, halogens, noble gases)

• The first letter is always capitalized the second (and third) are never capitalized.

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Compound

• A unique substance composed of two or more elements that are chemically combined (i.e. joined intimately, not just mixed together)

• Pure compounds have definite compositions and properties

• Require complex chemical procedures to separate into simpler substances (elements)

• Compounds include water, table salt, sugar, etc

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Density

• ratio of the mass of a substance to the volume of that mass

• usually measure in g/mL for solids and liquids; g/L for gases

• also a conversion factor relating the mass of a substance to it’s volume

• Specific gravity is the ratio of the mass of a substance to the mass of an equal volume of water

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A mixture is a combination of two or more substances in which the substances retain their distinct identities.

1. Homogenous mixture – composition of the mixture is the same throughout.

2. Heterogeneous mixture – composition is not uniform throughout.

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Mixtures

• Combinations of two or more substances• Can be separated by exploiting different physical

properties (filtration, distillation, crystallization, chromatography)

• Have chemical and physical properties that are different from the substances that make them up

• The percentages by mass of the components of a mixture can be varied continuously

No Calculator Vomit!!

• We want to use the correct number of Significant Figures!

• On the AP exam, you have to be within 1 sig fig in order to receive credit!

Counting Significant FiguresAtlantic / Pacific Method a. Absent Decimal- Start on “atlantic” side of

number & cross out all zeroes until 1st nonzero digit is reached, remaining digits are significant

b. Present decimal- start on the “pacific” side of the number & cross out all zeros until the 1st nonzero digit Is reached, remaining digits are significant

SI Units

Measurement Unit Symbol

Mass Kilogram kg

Length Meter M

Time Second s

Temperature Kelvin K

Quantity Mole mol

Energy Joule J

Pressure Pascal Pa

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Converting between units

• The standard method to convert between two different units is the factor-label or dimensional analysis method

• Dimensional analysis converts a measurement in one unit to another by the use of a conversion factor

• Conversion factors are developed from relationships between units

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The speed of sound in air is about 343 m/s. What is this speed in miles per hour?

1 mi = 1609 m 1 min = 60 s 1 hour = 60 min

343ms

x1 mi

1609 m

60 s

1 minx

60 min

1 hourx = 767

mihour

meters to miles

seconds to hours

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Temperature and its Measurement

• Temperature - measure of the intensity of the heat of a substance

• Thermometer - device to measure temperature

• Kelvin - K - SI unit of temperature• Celsius - °C - commonly used unit• Fahrenheit - °F - only used in USA

Temperature conversion factors                  

 

    Celsius to Kelvin      K = T in oC + 273     

                   

                   

    Kelvin to Celsius     oC = T in K - 273    

 

                   

                   

   

Celsius to Fahrenheit    

oF = (1.8 (T in oC)) + 32   

                     

                   

                   

    Fahrenheit to Celsius

   

  (T in oF - 32)/1.8  

  

           

               

                   

Measurements and Units

Measurement - determines the quantity, dimensions or extent of something1.Consist of two parts

a. a numerical quantity (1.23)b. a specific unit (meters)

Unit - a definite quantity adapted to as a standard of measurement

Features of Measured Quantities

When we measure a number, there are physical constraints to the measurement

Instruments and scientists are not perfect, so the measurement is not perfect (i. e., it has error)

The error in the measurement is related to the accuracy and the precision of the measurement

Accuracy and Precision

Accuracy – how close the measurement is to the “true” value (of course we have to know what the “true” value is)

Precision – is a measure of how closely individual measurements agree with one another.

Example: Accuracy and Precision

Equations for Precision and Accuracy

1. Precision2. Accuracy Percent Error % Error = (True value-Calculated Value) X 100 True Value

You will have to find the % Error for most of your labs!