Introduction to Science Science = the study of the world around us. Knowledge of the physical or material world gained through observation and experimentation.
The Nature of Science • Scientific law versus theory: • Scientific law: a summary of an observed natural event. • Scientific theory: a well tested, possible explanation of a natural event.
The Way Science Works… • Science involves critical thinking, or applying logic and reason to observations and conclusions. • Observation vs. Inference • Observation: descriptive of what you see, hear, taste, feel, smell • Inference: an assumption made as a result of an observation (not always correct!!)
Variables and Controls • A variable is anything that can change in an experiment. • Independent variable: The variable being changed or controlled by the scientist. • Dependent variable: The variable being measured or observed by the scientist. • A controlled experiment tests only one variable at a time.
The Scientific Method:A series of logical steps to follow in order to solve problems. • OBSERVE • FORMULATE A QUESTION • FORM A HYPOTHESIS • DESIGN AND CONDUCT AN EXPERIMENT • MAKE OBSERVATIONS • RECORD AND ANALYZE DATA • DRAW CONCLUSIONS • FORMULATE NEW QUESTIONS and CONTINUE CYCLE
Making Measurements • Measurements are made in this class using SI units. • LENGTH (m): distance between 2 points • VOLUME (L): space occupied. • MASS (kg): the amount of matter in an object. • WEIGHT (N): the force with which gravity pulls on a quantity of matter.
Precision vs. Accuracy • Accuracy: the extent to which a measurement approaches the true value. • Precision: the degree of exactness of a measurement. • A scale may be precise to the nearest 100th of a gram, or +/-0.01g
Precision vs. Accuracy increasing precision increasing accuracy
Density = mass/volume • Example 1: • What is the density of water if a 5 mL sample of water has a mass of 5 g? M D V
Example 2 • What is the mass of 10 mL of a liquid that has a density of 3.76 g/mL? d = m / v m = dv m = (3.76 g/mL)(10 mL) m = 37.6 g
Coke vs. Diet Coke • Which is less dense? Meaning which will float in water? • Coke or Diet Coke?
Calculations • Calculate the density of each: • A can of Coke has a volume of 355 mL and a mass of 394 g (assuming that the weight of the aluminum can is constant) • A can of Diet Coke has a volume of 355 mL and a mass of 355.1 g (assuming that the weight of the aluminum can is constant)
WHY is Diet Coke less dense? • There is less mass in the same volume (355 mL) • Coke has 39 grams of sugar in it to sweeten it (355 + 39 = 394 g) • Diet Coke only needs 0.1 g of Nutra Sweet to make is just as sweet as Coke (355 + 0.1 = 355.2 g)
Temperature Conversions • Temperature is a measure of the average kinetic energy in a system. • K = Kelvin • oF = degree Fahrenheit • oC = degree Celsius
Temperature Conversions • K = oC + 273 • oF = (1.8 x oC) + 32 • oC = (oF – 32) / 1.8
Percentage Error • Calculate this value in labs where the accepted value is given.
Organizing DataData is organized and presented in tables, charts, and graphs. GRAPHING... Graph - visual representation of data 1) title 2) x and y axis labeled 3) units for both the x and y axis 4) scale is evenly and correctly spaced for data 5) legend when appropriate
LINE GRAPH LINE GRAPH: best for displaying data that change. • Independent Variable: x-axis • Dependent variable: y-axis
BAR GRAPHS BAR GRAPH: useful when you want to compare data for several individual items
PIE CHARTS PIE CHART: ideal for displaying data that are parts of a whole.
Scientific Notation/Powers of 10 Significant Figures Dimensional Analysis (Factor Label Method)
MATH IS THE LANGUAGE OF CHEMISTRY!!!
Scientific Notation Scientist use special notation to expressvery largeorvery smallnumbers. Example I: 300,000,000 m/sec can be written as… 3 x 108 m/sec Ex II: 1,007,000,000 sec can be written as… 1.007 x 109 sec Ex III: 0.000 000 000 004 76 m can be written as… 4.76 x 10-12 m
Converting Metric Measurements(PART 4 of Things to Know and Love) To convert, move the decimal place the number of stairs you step on in the direction you are traveling OR use dimensional analysis. kilo- 103 hecto- 102 deca- basic unit 101 1 deci- Example: 3.75 km = ? mm 10-1 centi- 10-2 milli- ? = 3,750,000 mm 10-3
Video • Powers of Ten
SIGNIFICANT FIGURES • Scientists indicate the precision of measurements by the number of digits they report = sig. figs. • A value of 3.52 g is more precise than a value of 3.5 g • All known digits plus one estimated digit ** the equipment used for a measurement will determine the number of sig. figs.
Significant Figures Atlantic - Pacific Rule: Decimal Present: Count from the Pacific side Decimal Absent: Count from the Atlantic side Start counting at the first non-zero number and count until you reach the end of the number Ex. I: 3.00700 Decimal Present… Pacific (left)… 6 sig. figs. Ex. II: 300,700 Decimal Absent… Atlantic (right)… 4 sig. figs. (the last 2 zeros are PLACE HOLDERS)
REVIEW Determine how many significant figures are in each of the following measurements. • 0.0034050 L ___________ • 33.600 m ___________ • 7500.0 g ___________ • 47,900 mm ___________ • 7,000,000,001 miles ___________ • 8.07 Hz ___________ 5 (the first 3 zeros are PLACE HOLDERS) 5 5 3 (the last 2 zeros are PLACE HOLDERS) 10 3
More practice… Round the following measurements off so that they each contain 3 significant figures. • 366.2 L ___________ • 9,047,022 mg ___________ • 12.76 g ___________ • 999.9 J ___________ 366 L 9,050,000 mg 12.8 g 1.00 x 103 J Notice this one must be in scientific notation to have 3 sig. figs.
Significant Figures in Calculations When multiplying and dividing, limit and round to the least number of significant figures in any of the factors. Example: 23.0 x 432 x 19 = 188,784 = 190,000 The answer is expressed as 190,000 or 1.9 x 105 since 19 has only two sig. figs.
Significant Figures in Calculations When adding and subtracting, limit and round your answer to the least number of decimal places in any of the numbers involved in the calculation. Example: 123.25 + 46.0 +86.257 = 255.507 = 255.5 The answer is expressed as 255.5 since 46.0 has only one decimal place.
REVIEW Perform the prescribed operations. Round your answers to the proper # of sig. figs. • 36.57 m / 3.21 s = ___________ • 41.376g + 13.3g + 42.9g=___________ • 5.67 m x 13.44 m ___________ • (5.83 m/ 2.67 s) /2.1 s ___________ • 9.374 V x 6 ___________ 11.4 m/s 97.6 g 76.2 m2 1.0 m/s2 60 V From now on, we will round all our answers to the correct # of significant figures.
EXTRA REVIEW • Using a calculator for EXPONONETS (EE, EXP or x10x button) • Example 1: (5.02 x 10-3) x (6.3369 x 105) = 3181.1238 *put in correct sig figs = 3 sig figs = 3180 or 3.18 x 103
Example 2 (use EE button!) • (2.99 x 106) x (2.334 x 10-3) = = 6978.66 • 3 sig figs • 6980
DIMENSIONAL ANALYSIS • How old are you in seconds? • Go from number of years to number of seconds. EX: 15 years old _____ seconds old. To do this, you need to use CONVERSION FACTORS (a ratio of equivalent values used to express the same quantity in different units)
Given Information: NOTETAKERS General Format... given going to = X coming from
GIVEN INFORMATION 1 kildurkin = 18 gallons 2 farkins = 1 kildurkin 1 hogshead = 63 gallons 1 barrel = 3.3 bushels 1 bushel = 8 gallons
Make a UNIT CONVERSION MAP Draw connections between the units in the conversion factors… (as you draw connections, check that conversion factor off the list) It’s kind of like a road map…
hogshead kildurkins farkins gallons barrel bushel
Dimensional Analysis Performing these conversions is a lot like going on a road trip.
ROAD TRIP!!! Let’s say you want to travel from Oracle Jct to Casa Grande... You must travel through Tucson… a two part trip.
Rule: You need a map. Sometimes the map can be in your head. But, not at first. (show all work!!)
Let’s calculate • Convert 14 gallons to kildurkins
Now you try one. How many farkins is 3.00 bushels? End Here hogshead kildurkins farkins gallons Start Here barrel bushel This will require 3 Conversions.
farkins bushels gallons kildurkins 8.0 gallons 1.0 kildurkin 2.0 farkins 3.00 bushels X X X 1.0 bushel 18 gallons 1.0 kildurkin = 2.67 farkins