2Must repeat several times. Scientific MethodObservationHypothesisIf hypothesis is false, propose new hypothesis.ExperimentTheoryLawMust repeat several times.
3Models, Laws & Theoriesmodel: visual, verbal and/or mathematical explanation of data; can be -tested -used to make predictions theory: explanation based on supported hypothesis -broad principle of nature supported over many years -can be modified -can lead to new conclusions
4Models, Laws & Theorieslaw: describes something known to happen without error -doesn’t explain why it happens -there are no exceptions -several scientists come to the same conclusion
5DataWhen making observations or gathering information, we separate the data into 2 types:1. qualitative-uses the 5 senses-physical characteristics2. quantitative-numerical data-measurable
6Variables There are 2 types of variables when doing an experiment: 1. independent: variable you change2. dependent: variable that changes due to a change inthe independent variable.It is also important to have controls, or standards for comparison.
7Significant Figuressignificant figures: number of all known digits in a measurement plus one estimated digit.-allows more precision in measurement-not all measuring devices show the same precisionExample: In the following measurement, what are the known values and what is the estimated value?16.25 mLknown = 162estimated = 5
8Significant Figures-Rules The easiest way to determine significant figures of a given number is by using the Pacific/Atlantic rules.1. Decimal point PRESENT, start from the PACIFIC.-Begin counting on the left hand (Pacific) side of thenumber. Move toward the right and start with thefirst nonzero number.has 7 significant figureshas 2 significant figures
9Significant Figures-Rules 2. Decimal point ABSENT, start from the ATLANTIC.-Begin counting on the right hand (Atlantic) side ofthe number. Move toward the left and start withthe first nonzero digit.1200 has 2 significant figures1207 has 4 significant figuresZeros that act as placeholders are not significant:and 1200
10Significant Figures Practice 1 Copy the following questions and answer.Determine the number of significant figures in the following numbers.1) ) )2) ) )3) )9) ) 2.00x102 15)10) )11) )
11Significant Figures and Rounding Suppose you are asked to find the density of an object with a m=of g and whose V=14.2 cm3.Using a calculator, you get , which has 8 significant figures. Does this answer make sense?No. The mass only has 4 sig figs and the volume has 3. Your answer would be more precise than the starting information.
12Significant Figures and Rounding How would you correctly round this?By using the starting data with the fewest sig figs (when multiplying/dividing), which is 3: g/cm3-when adding/subtracting, your answer will have the smallest number of decimal places based on the starting information.3.12 m m = 6.32 m = 6.3 m
13Significant Figures Practice 2 Perform the following operations expressing the answer in the correct number of significant figures.1) m x m2) m2 ÷ 42 m3) mL mL + 6 mL4) g – 28.9 g5) x103 m2 ÷ x102 mRound all numbers to four significant figures.6) kg 8) g 10) m7) g 9) mL
14SI Units and Derived Units The SI base unit is the unit in a system of measurements that is based on an object or event in the physical world.UnitQuantitySymbolAbbrev.lengthlmetermmasskilogramkgtimetsecondstemperatureTKelvinKamount of substancenmolemolelectric currentIampereAluminous intensityIvcandelacd
15Temperature There are three possible temperature scales: Celsius-based on metric system-based on temp when water freezes andboilsKelvin-SI Unit-based on the idea of absolute zero, thelowest possible theoretical temperature-will discuss more in Ch 14 (Gas Laws)3. Farenheit-what we are used to using
16Converting Temperature Celsius to Kelvin / Kelvin to CelciusTK = TCTC = TK2. Celsius to Farenheit / Farenheit to CelsiusTC = (TF -32oF)5oC9oFTF = TC 9oF oF5oC
17SI Units and Derived Units Not all quantities can be measured with base units.derived unit: unit that is defined by a combination of base units-volume: space occupied by an object; unit is the liter, L, for liquids and gases, or cubic centimeter, cm3, for solidsV = l x l x l-density: ratio of the mass of an object to its volume; unit is g/mL or g/cm3 since 1 mL = 1cm3D = m/V
18Prefixes Prefix Symbol Meaning Multiple of Base Unit 10n yotta- Y septillion1,000,000,000,000,000,000,000,0001024zetta-Zsextillion1,000,000,000,000,000,000,0001021exa-Equintillion1,000,000,000,000,000,0001018peta-Pquadrillion1,000,000,000,000,0001015tera-Ttrillion1,000,000,000,0001012giga-Gbillion1,000,000,000109mega-Mmillion1,000,000106kilo-kthousand1000103hecto-hhundred100102deca-daten10101basedeci-dtenth0.110-1centi-chundredth0.0110-2milli-mthousandth0.00110-3micro-millionth10-6nano-nbillionth10-9pico-ptrillionth10-12femto-fquadrillionth10-15atto-aquintillionth10-18zepto-zsextillionth10-21yokto-yseptillionth10-24
19Converting Between Prefixes Dimensional analysis is a method of problem-solving that focuses on the units used to describe matter. A conversion factor is a ratio of equivalent values used to express the same quantity in different units. -they change the units of a quantity without changing its value -ratio of units, such as 1 km 1000m -set up so the units you don’t need cancel out 48 m x 1 km = km 1000 m
20Dimensional AnalysisIt is common in scientific problems to use dimensional analysis to convert more than one unit at a time.What is the speed of 550 m/s in km/min?Convert m to kmConvert s to min
21Dimensional AnalysisSometimes we need to convert from metric to standard (and vice versa).-some of these common conversions you will need to know are:1 cm3 = 1 mL 60 s = 1 min1 in = 2.54 cm 60 min = 1 hr1 ft = 12 inPractice:152 cm = ____ m s = ____ hr42.5 in = ____ ft mL = ____ cm3
22Accuracy and Precision Density collected by Three Students.ABCT1 (g/cm3)1.541.401.70T2 (g/cm3)1.601.681.69T3 (g/cm3)1.571.451.71Avg. (g/cm3)1.51accuracy: how close a measured value is to an accepted value.precision: how close a series of measurements are to one another.-may not be accurateExample: For the following data, the actual density value is 1.59 g/cm3.
23Percent Errorpercent error: ratio of the difference in the measured value and accepted value divided by the accepted value multiplied by 100% error = │measured value – accepted value│ x 100accepted valueEx: Calculate the % error of Student A’s Average Data.% error = │1.57 g/cm3 – 1.59 g/cm3 │ x 1001.59 g/cm3= │-0.02 g/cm3 │ x 100= 0.02 g/cm3 x 100= 1 %
24Accuracy & Precision Practice Density collected by Three Students.ABCT1 (g/cm3)1.541.401.70T2 (g/cm3)1.601.681.69T3 (g/cm3)1.571.451.71Avg. (g/cm3)1.51Calculate the percent error for each of the three students (A, B, C). The accepted value is 1.59 g/cm3)
25Graphing-You TryGraph the data set A for T1, T2, and T3 using the rules you know.Density collected by Three Students.ABCT1 (g/cm3)1.541.401.70T2 (g/cm3)1.601.681.69T3 (g/cm3)1.571.451.71Avg. (g/cm3)1.51
26Graphing In chemistry, we mainly deal with line graphs. A graph is used to reveal patterns by giving a visual representation of data.a. must know the independent (x axis) and dependentvariable (y axis)b. determine the range of data that needs to beplotted for each axis: try to take up at least ¾ of thepaper-use a pencil and rulerc. number and label each axis: don’t forget the unitsd. plot the points and draw a line of best fit-curved or straighte. title the graph
27Graphing PracticeComplete the problem-solving lab at the bottom of page 44 in your textbook. Answer the Analysis and Thinking Critically questions on the back of the graph.
29Scientific NotationValues in science are often very large or very small, requiring a lot of zeros.-ex: the distance between Earth and Neptune is4,600,000,000,000 m apart and the speed of lightis 300,000,000 m/s.this is a lot of zeros to keep track of.Q: What do scientists do?A: they use scientific notation, a short hand method ofwriting extremely large or small numbers, to maketheir calculations easier.
30scientific notation is a value written as a simple number multiplied by a power of 10. Power of 10 equivalents:= 10,000= 1000= 100= 10100 = 110-1 = 0.110-2 ===
31Writing Scientific Notation 1. Write the first 2 or 3 digits as a simple number withonly one digit to the left of the decimal point.2. Count the number of decimal places you move thedecimal. This will give you your power of 10.-If you move the decimal to the left the power of ten will be positive.-If you move the decimal to the right the power of ten will be negative.If you must adjust the decimal:-if you move it to the left, you add to the exponent-if you move it to the right, you subtract the exponent
32Dividing with Scientific Nototation Example Lets calculate the time it takes for light to travel from Neptune to Earth. The speed of light is 3.0x108m/s and the distance from Neptune to Earth is 4.6x1012m.-Use the formula v = d/t-Rearrange to solve for t: t = d/v-d = 4.6x1012m, v = 3.0x108m/s, t = ?- t = 4.6x1012m = 1.5x104s (no adjustment)3.0x108m/s
33Dividing with Scientific Notation Practice You may not use a calculator.Convert the following into scientific notation.Convert the following into common form.x x104x x102Solve the following:x105 ÷ 3.0x102x104 ÷ 5x102x106 ÷ 4.00x103
34Multiplying with Scientific Notation ExampleIf it takes 2.7 x 1023 seconds for light to travel from one planet to another, how far apart are the planets? Remember light travels at a speed of 3.0 x 108 m/s.-Use the formula v = d/t.-Rearrange to solve for d: d = vt-d = ?, v = 3.0 x 108 m/sd = vt = (2.7 x1023 s) (3.0 x 108 m/s)= 8.1 x 1031 m (no adjustment necessry)
35Multiplying with Scientific Notation Practice You may not use a calculator.Review with dividing:1.2x103 ÷ 2.4x1044.6x10-3 ÷ 2.3x10-56.02x105 ÷ 2.0x102Multiplying:4. (1.2x103)(2.4x104)5. (4.6x10-3)(2.3x10-5)6. (6.02x105)(2.0x102)7. (2.70x105)(3.0x10-2)
36Cumulative Scientific Notation Practice You may not use a calculator.1. Write the following measurement in scientific notation.a. 37,500,000,000,000,000,000,000 mb kg2. Write the following values in long (standard) forma x 103 grams b x 10-6 km3. Multiply.a. (3.5 x 1012)(2.2 x 105) b. (7.5 x 10-3)(1.2 x 10-2)4. Dividea x b x 10-31.2 x x 10-7
37Combined Measurement Practice Show all work, including units!!Metrics: Convert the following:1) 35 mL = ____ L 2) kg = ____ gDimensional Analysis: Convert the following:3) 3500 s = ____ hr 4) 4.2 L =_____ cm3Scientific Notation: Convert to scientific notation:5) ) )Scientific Notation: Convert to standard notation:8) 1.5x ) 3.35x10-6Calculations: using Scientific Notation10) (1.5 x 103)(3.5x105) 11) (3.45x10-3)/(1.2x 10-2)12) (7.6x10-3)(8.2x107 ) 13) (6.8x107)/(2.2x10-5)