unit 1: foundations of chemistry chapters 1, 2, & 3 chemistry 1l cy-creek high school
TRANSCRIPT
Unit 1: Foundations of Chemistry
Chapters 1, 2, & 3
Chemistry 1L
Cy-Creek High School
Scientific Processa.k.a. Scientific Method
Why do we need it?
What is the Scientific Process?
A systematic approach to problem solving Generally Composed of the following parts:
– Observations– Hypothesis– Experiment– Conclusion
Observations
Qualitative (Quality)- characterized as data you use your senses to describe– Ex: color, texture, emotion, taste, smell, etc.
Quantitative (Quantity, #)- something that can be measured– Ex: 212°F, 3 m, 1.0 L
What is an Inference?
How we interpret the observation
Scientific Process
Joe baked a cake for his mother’s birthday. When the cake was taken from the oven Joe noticed that the cake had not risen. Joe guessed that the oven had not heated to the right temperature. He set up this experiment to test his idea.
First, Joe put a thermometer in the oven. He then turned the oven dial to 350°F. He noticed that the preheating light came on when he turned the oven on. He waited until the preheating light went out. The light’s going out indicated that the oven was up to temperature. Joe then read the thermometer within the oven. It read 350°F. Joe concluded that the oven was working correctly.
Inference or Observation?
Joe thought the cake recipe was good. The preheating light came on when the
oven was turned on. The thermometer read 350°F. The cake did not rise.
Now What?
Classification – group similar observations together into categories
Hypothesis - Educated guess
Models – shows information about another object or event
Experiment Time!
Test your hypothesis
How? Controlled experiment – control group
(benchmark or comparison) and one or more changing variables
The Conclusion (not quite yet)
Analyze your data Look back at your hypothesis Calculate error
THEN, make your judgment (conclusion)
Measurement & Significant Figures
Nature of Measurement
MeasurementMeasurement - quantitative observation - quantitative observation consisting of 2 partsconsisting of 2 parts
Part 1 – numberPart 1 – number
Part 2 - scale (unit)Part 2 - scale (unit)
Examples:Examples:20 grams20 grams
6.63 6.63 Joule seconds Joule seconds
International System(le Système International)
Based on metric system and units Based on metric system and units derived from metric system.derived from metric system.
*Called *Called SI unitsSI units**
The Fundamental SI Units
Derived Units
Units obtained by a mathematical operation performed on base units.
Area L x W cm x cm = cm2
Volume L x W x H cm x cm x cm = cm3
Density mass / volume g / mL
Accuracy and Precision
• AccuracyAccuracy refers to the agreement of a refers to the agreement of a particular value with theparticular value with the truetrue value.value.
• Precision Precision refers to the degree of refers to the degree of agreement among several elements of agreement among several elements of the same quantity.the same quantity.
Label each experiment
True Value = 5.000g
Accurate & Precise Precise but not accurate
Trial 1 – 5.003g Trial 1 – 5.500g
Trial 2 – 5.002g Trial 2 – 5.503g
Trial 3 – 5.001g Trial 3 – 5.499g
Neither Accurate or Precise
Trial 1 – 5.400g
Trial 2 – 5.200g
Trial 3 – 5.905g
Uncertainty in Measurement
A digit that must be A digit that must be estimatedestimated is called is called uncertainuncertain. A . A measurementmeasurement always has always has
some degree of uncertainty.some degree of uncertainty.
Reading measuring devices
Try Again
How long is the green line?
Rules for Counting Significant Figures - Overview
1.1. Nonzero integersNonzero integers
2.2. ZerosZeros• leading zerosleading zeros• captive zeroscaptive zeros• trailing zerostrailing zeros
3.3. Exact numbersExact numbers
Rules for Counting Significant Figures - Details
Nonzero integersNonzero integers always count as always count as significant figures.significant figures.
3456 3456 has has
4 4 sig figs.sig figs.
Rules for Counting Significant Figures - Details
ZerosZeros• Leading zerosLeading zeros do not count as do not count as
significant figures.significant figures.
0.00.0486486 has has
33 sig figs. sig figs.
Rules for Counting Significant Figures - Details
ZerosZeros• Captive zerosCaptive zeros always count as always count as
significant figures.significant figures.
16.16.007 7 hashas
4 4 sig figs.sig figs.
Rules for Counting Significant Figures - Details
ZerosZeros• Trailing zerosTrailing zeros are significant only are significant only if the if the
number contains a decimal point.number contains a decimal point.
9.39.30000 has has
44 sig figs. sig figs.
Rules for Counting Significant Figures - Details
ZerosZeros• Trailing zerosTrailing zeros are are notnot significant when significant when
there is there is notnot a decimal point a decimal point
93930000 has has
22 sig figs. sig figs.
Zero’s Chant
Leading zeros never count,
Captive zeros always count,
Trailing zeros only count if there’s a decimal in the number!
Rules for Significant Figures in Mathematical Operations
Multiplication and DivisionMultiplication and Division: : # sig figs in # sig figs in the result equals the number in the least the result equals the number in the least precise measurement used in the precise measurement used in the calculation.calculation.
6.38 6.38 2.0 = 2.0 =
12.76 12.76 13 (2 sig figs)13 (2 sig figs)
Rules for Significant Figures in Mathematical Operations
Addition and SubtractionAddition and Subtraction: : # sig figs in # sig figs in the result equals the number of the result equals the number of decimadecimall placesplaces in the least precise in the least precise measurement.measurement.
6.8 + 11.934 =6.8 + 11.934 =
18.734 18.734 18.718.7
Scientific Notation and Dimensional Analysis
How to use these tools
Scientific Notation - Overview
Used to make really large or small numbers manageable.
Consists of 2 parts:– A number with only 1 number to the left of the
decimal place (base number)– 10 to a power, either + or –
5.234 x 103 8 x 10-5 106 = 1 x 106
Scientific Notation - Overview
If the 10 has a + power the decimal moves to the right
Ex. 1.5 x 103 = 1500 If the 10 has a - power the decimal moves to
the left
Ex. 3.5 x 10-6 = 0.0000035 All BASE numbers are significant digits!
Scientific Notation – With Calculator
Use the “2nd” then “,” to enter the “EE” which stands for the x10
Use the “(-)” to change to negative exponent if negative
Enter the number of the exponent
Scientific Notation – With Calculator
Examples:
1. (5.4 x 103) + (6.00 x 102) =
5.4 “EE” 3 + 6 “EE” 2 =
2. (3.42 x 10-5) – (2.5 x 10-6) =
3.42 “EE” “(-)” 5 – 2.5 “EE” “(-)” 6 =
Scientific Notation – With Calculator
3. (6.5 x 10-5)(3.5 x 106) =
6.5 “EE” “(-)” 5 x 3.5 “EE” 6 =
4. 10-8 / 103 =
1 “EE” “(-)” 8 ÷ 1 “EE” 3 =
Dimensional Analysis
Organized approach to problem solving Uses conversion factors to find your desired
outcome– Conversion factors: any two quantities that
are equal– Ex. 1 in = 2.54 cm; 1 lb = 454 g; 1 qt = 946
mL
Dimensional Analysis
It is basically multiplying fractions! Units cancel diagonally until you are left with
your desired unit Solve by multipling the numbers above the
line & dividing the numbers below the line
Dimensional Analysis
1. Write down the units you are looking for.2. Write down the number & unit given in the
problem.3. Decide what conversion factor(s) you need
to use.4. Cancel Units which are diagonal5. Multiply everything above and below the
line.6. Divide the number above the line by the
number below the line.
Dimensional Analysis
1. ? Seconds has a 16 year old lived.
2. ? Lbs is a 200,000 g sumo wrestler.
3. ? L in a 6 pack (ea. 12 oz) of soda.
Dimensional Analysis – Metric Units
1. Base Units (pg 26) - mass: grams - length: meters - volume: liters - time: sec - temp: °C, K - amt: mole
2. Based on powers of 10- Common Prefixes and powers
kilo k 103
centi c 10-2
milli m 10-3
micro μ 10-6
nano n 10-9
Dimensional Analysis – Metric Units
1. Go from beginning unit to stem (meter, liter, gram, second)
2. Go from stem to unit that you want
3. Always use a whole (+) positive exponent number
4. Put the + number as the exponent of the smaller unit
Matter: Properties & Changes
Subtopics: Density & Graphing
States of Matter
Solid– Molecules or atoms in a rigid pattern
(crystal lattice)– High intermolecular attractions– Definite shape and volume
Liquid– Particles not in definite pattern– Relatively high intermolecular
attraction– Definite volume = shape of container
States of Matter
Gas– Particles have no pattern– Low intermolecular attraction– No definite shape or volume
Properties of Matter
What is a Property?– Characteristics that describe matter or how it behaves
Physical – determined without a chemical change
– Extensive – vary with amount of matter (Ex. Mass, volume, length, area)
– Intensive – does not vary with amount (Ex. Density, color, odor, melting point, solubility)
Chemical – can only be determined by a chemical change
Ex. Flammability, reactivity with acid, stability of a compound (how easily it decomposes)
Changes of Matter
Physical Changes – does not involve a change in chemical identity– Ex: boiling, freezing, melting, dissolving,
evaporating, and crystallizing
Changes of Matter
Chemical Changes – new substances are formed in the reaction– Ex: iron rusting,
copper oxidizing, wood burning, silver tarnishing
Evidence for Changes of Matter
Color Change Gas produced without
heating Precipitate formed New odor develops Large amount of heat
or light produced
Energy in Chemical Reactions
All chemical changes also involve some sort of energy change.
Energy is either taken in or given off as the chemical change takes place.
– Exothermic: heat energy is released– Endothermic: heat energy is
absorbed Photosynthesis is probably the most
important endothermic process on earth.
Density
Mass per unit volume (mass/volume)
Units:– Liquids - g/mL or g/cm3
– Gases - g/L
Density
Density remains constant (same ratio) for a material unless temperature changes.
A gold bar is cut in half. What happened to its density?
What happened to its value?
Graphing
1. Use graph paper.2. Use a ruler to draw axes.3. Choose a descriptive title.
• Relate info on the 2 axes.• Ex: Relationship of Mass to Volume
4. Label axes & give units of measurement. Ex. Temperature (°C)
5. Choose a scale that will fill entire page.• You do not have to start with zero in the corner!• Subtract lowest from highest value ÷ by # lines.
Graphing
6. Plot data points & circle each point (point protector)
7. Draw a Best Fit Line (smooth line) or curve to indicate a general trend of data points.
DO NOT CONNECT DOT TO DOT!
8. Extrapolate data beyond data points using dotted lines.
End of Unit 1 Notes!
Prepare for the Unit 1 Test on 9/11/2008