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Introduction to Chemistry

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http://www.youtube.com/watch?v=izeuGr 0lbN0 http://www.youtube.com/watch?v=izeuGr 0lbN0 http://www.youtube.com/watch?v=izeuGr 0lbN0 http://www.youtube.com/watch?v=izeuGr 0lbN0

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What is Chemistry? The study of the composition of matter and the changes that matter undergoes The study of the composition of matter and the changes that matter undergoes

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Five major branches of chemistry Organic Organic

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Inorganic Inorganic

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Analytical Analytical Physical Physical Biochemistry Biochemistry

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Why study Chemistry??? Pure Chemistry Pure Chemistry Applied Chemistry (Technology) Applied Chemistry (Technology)

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Chemistry plays a big part in our lives We are in the “Age of Plastics” We are in the “Age of Plastics” High “strength to weight” ratio High “strength to weight” ratio

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Energy New fuels New fuels New insulation material New insulation material

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Energy from the sun Energy from the sun Hydrogen cells Hydrogen cells Storage batteries Storage batteries

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Medicine and Biotechnology Medicines Medicines Surgical breakthroughs Surgical breakthroughs Genetic research Genetic research

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Agriculture Protect crops Protect crops Increase food supply Increase food supply Increase strength and vitality of plants Increase strength and vitality of plants

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Environment Pollution Pollution Catalytic converters Catalytic converters Acid rain Acid rain Ozone layer Ozone layer

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SCIENTIFIC METHOD

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1. Observation Gather data: qualitative or quantitative

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2. Hypothesis t tentative explanation for what is observed (educated guess)

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3. Experiments – set of controlled observations that test a hypothesis

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–Independent variable – one you are going to change

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–Dependent – changes depending on the independent variable

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–control – standard for comparison –Model – visual, verbal and/or mathematical explanation of experimental data

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Conclusion – judgment based on the information obtained – judgment based on the information obtained

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Theory – explanation that has been supported by MANY experiments – explanation that has been supported by MANY experiments

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Scientific Law – describes a relationship in nature that is supported by many experiments. – describes a relationship in nature that is supported by many experiments.

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Types of observations Qualitative observations – describe a substance without using numbers “It is heavy” “ It is blue” “It smells”

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Quantitative observations – use numbers 87 millimeters 10 liters 4.0 g/ml

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Scientific Notation 765,000,000,000 7.65 X 10 11 Move decimal to the left – is positive 0.0000084 8.4 X 10 -6 Move decimal to the right – is negative Samples on handout

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Write in standard notation 4.5 x 10 -5 0.000045 3.42 x 10 4 34200

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Is how close a measurement is to the correct or accepted value

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How close a series of measurements are to each other (how close a measurement is to other measurements of the same thing) Dartboard example

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Assures the certainty of measurements For any measurement, scientists only record all the digits they are certain of, plus one estimated figure Together, they are called “significant figures”

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Sample 6.2345 meters All the digits are significant. Which one is the estimated and which are certain? 6,2,3,4 are certain 5 is estimated

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A scientist measures 89 seconds All are significant Which are certain and which are estimated? 8 is certain 9 is estimated

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R ULES FOR COUNTING SIGNIFICANT FIGURES IN A MEASUREMENT Rule 1 – all nonzero digits are significant – 1,2,3,4,5,6,7,8,9 – are significant Rule 2 – Final zeroes to the right of the decimal point are significant 3.4000 5 sig figs

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Rule 3 – zeroes between two significant digits are significant 304 3 sig figs 70009 5 sig figs

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Rule 4 – zeroes used for spacing the decimal point are not significant 0.00045 2 sig figs 0.02387 4 sig figs

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Rule 5 – for numbers in scientific notation, all of the digits before “x 10 x ” are significant 5.730 x 10 9 4 sig figs

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7000 1 sig fig 7000. 4 sig figs

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Let’s practice!! 135.3 4 sig figs 4.6025 5 sig figs 200,035 6 sig figs 0.0000300 3 sig figs

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2.0000300 8 sig figs 0.002 1 sig fig 4.44 x 10 3 3 sig figs 2.0 x 10 -2 2 sig figs

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10.00 4 sig figs 10 1 sig fig 102,000 3 sig figs

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Solving problems with sig figs Multiplying and dividing with sig figs The answer you get must be rounded to the same number of sig figs as the measurement with the lowest number of sig figs (that you multiplied or divided)

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Example Multiply 4.610 feet by 1.7 feet. Express your answer in correct sig figs 4.610 x 1.7 = 7.837 How do you round it? 4.610 has 4 sig figs 1.7 has 2 sig figs Round answer to 2 sig figs Answer = 7.8 square feet

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Divide 653 miles by 3 hours. Express in the correct number of sig figs Answer = 200 miles/hour

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Adding and Subtracting with sig figs When adding or subtracting measurements, the answer cannot have more certainty than the least certain measurement. Answer must have the same number of sig figs to the right of the decimal point as the measurement with the fewest sig figs to the right of the decimal point

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Example 4.271 grams (3 sig figs to the right of decimal) 2 grams (0 sig figs to the right of decimal) + 10.0 grams (1 sig fig to the right of decimal) 16.271 grams round 16 grams

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Sample Add these measurements: 4.35 seconds and 212.2 seconds. Express your answer using correct sig figs Answer = 216.6 seconds Add these measurement: 2.423 meters + 0.001365 meters Answer = 2.424 meters

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Measurement units and unit conversions Common metric base units: Distance or length – meter m Mass – gram g Volume – liter L Temperature – degree Celsius o C Time – second s Also use Kelvin (K) for temperature

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Metric Prefixes

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Common metric prefixes Micro Example 1 μm = 0.000001 m 1 x 10 6 μm = 1 m

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milli m 0.001 or (1 x 10 -3 ) Example 1 mg = 0.001 g 1000 mg = 1 g

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centi c 0.01 or ( 1 x 10 -2 ) Example 1 cm = 0.01 m 100 cm = 1 m

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Deci d 0.1 or (1 x 10 -1 ) Example 1 dL = 0.1 L (liter) 10 dL = 1 L

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kilo k 1000 or (1.0 x 10 3 ) Example 1000 g = 1 kg

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Unit Conversions Also called “factor labeling” How many inches in 2 feet? How many feet in 36 inches? You just did a unit conversion!!!!!! Look at board

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Must use correct “conversion factor” 230 cm = ? m Must know that 100 cm = 1m Write possible conversion factors 1m or 100 cm 100 cm 1 m

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Write the number you are converting first Multiply it by the conversion factor that has the unit you want your answer to be in on the TOP This guarantees that you will divide or multiply when you are supposed to.

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230 cm x 1 m = 2.3 m 100 cm The top and bottom units cancel out and the only unit left is the one you want you answer to be in!!!!!

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Text – practice on pgs. 36 -37 Show you two step conversions on board 4500 cm = ? km

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Derived units What does “derived” mean? A derived unit is a measurement unit created by multiplying or dividing other units Miles per hour words per minute

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Area Length x width ft x ft = ft 2 ft 2 is a derived unit (derived from two length units) m x m = m 2 m 2 is a derived unit (derived from two length units)

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Length x width x height ft x ft x ft = ft 3 m x m x m = m 3 cm x cm x cm = cm 3

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Describes how dense something is How heavy it is for its size Density = mass divided by volume D = M V M = D x V V = M D

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Since you are dividing two different measurements, the unit for density is a DERIVED UNIT. Derived from a mass measurement and a volume measurement g/mL g/L

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Calculate the density of a substance with a mass of 24.3 g and a volume of 32.9 mL. Use the correct unit and the correct number of sig figs in your answer. D = M V D = 24.3 g 32.9 mL Ans. = 0.739 g/mL

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What is the volume of an object with a density of 1.25 g/mL and a mass of 281 g? V = M D V = 281 g 1.25 g/mL g cancels, so units are mL for answer V = 225 mL

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Text – Pg. 46 #20, 21 Pg. 47 #25

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