2Measurements Quantities with both a number and a unit Used to measure a physical property.5 gramsMass2 litersVolume1.6 metersLength
3Why does this matter? In chemistry, we make lots of measurements Examples?We need to have a common language of measurement so that we can understand each other’s results.
4Scientific NotationIn chemistry, we deal with numbers that are very big and very smallHow many water molecules are in the beaker?600,000,000,000,000,000,000,000What is the width of a water molecule?meters
5Scientific NotationHow can we express big and small numbers in a simpler way?Powers of 1010 = = 100100 = = 10-11000 = = 10-210,000 = = 10-3Exponent = # of places you move the decimal point to get behind the first digitLeft = positiveRight = negative
7Practice problem Express the following numbers in exponential form: 100,0001000.001.11
8Scientific notationTo put a number in scientific notation, express it as the product ofA number between 1 and 10A power of 10Example:5000 meters = 5 x 1000 meters= 5 x 103 meters.025 liters = 2.5 x .01 liters= 2.5 x 10-2 liters
9Practice problemsExpress the following numbers in scientific notation:5280 feetgrams602,000,000,000,000,000,000,000 atoms
10Accuracy v. PrecisionAccuracy = how close your measurements are to the correct valueEx: I can run a mile in 7 minutesIf you measure my mile time and get 7 minutes, you are highly accurateIf you measure my time and get 8 minutes you are inaccurate
11Precision Precision = how close your measurements are to each other If you measure my mile time and get 7 minutes three times, you are very preciseIf you measure my mile time and get 8 minutes three times, you are still very preciseBut you are not very accurate.
13ErrorError is the difference between your measurement and the accepted valueError = experimental value – accepted value
14Practice problem Calculate the error: Experimental value = 1 meter Accepted value = 1.02 metersExperimental value = 10.7 secondsAccepted value = 10.5 seconds
15Percent Error How much error is a lot of error? If my measurement of the weight of a car is 10 lbs too much, do I care?If my measurement of the weight of a baby is 10 lbs too much, do I care?
16Percent errorPercent error is an expression of error as a percentage of the accepted value𝑃𝑒𝑟𝑐𝑒𝑛𝑡 𝑒𝑟𝑟𝑜𝑟= |error| 𝑎𝑐𝑐𝑒𝑝𝑡𝑒𝑑 𝑣𝑎𝑙𝑢𝑒 x 100%
17Percent error practice Mr. Tunney’s new car weighs 2795 lbs. The dealership weighs the car at 2805 lbs.What is the error? What is the percent error?When Mr. Tunney was born, he weighed 9.5 lbs. The doctor weighed him at 19.5 lbs.
18Percent error practice Felipe sticks a thermometer in a pot of boiling water, and measures its temperature as 99.1°C. The true temperature of boiling water is 100°C.What is Felipe’s error? What is his percent error?
19Significant FiguresThe accuracy of our measurements is limited by the accuracy of our toolsWhat’s the smallest increment marked on this scale?
20Significant FiguresWhen making measurements, you can record as many digits as your tool measures, and you can estimate one more digit.All of these digits have useful information, so they are called significant figures
21Significant figures? Can I measure this length as 11.754325 cm? Why/why not?How many significant figures should this measurement have?
22Significant figure rules How do I know how many significant figures a given measurement has?Example: I tell you I am meters tall. How many significant figures are there?Rules:All nonzero digits are significantAll zeroes between nonzero digits are significantLeftmost zeroes are not significantRightmost zeroes are significant if they follow a decimal point or are followed by a decimal point
23Significant Figures Rules All nonzero digits are significantHow many significant figures:2201000345
24Significant figure rules All zeroes between nonzero digits are significantHow many sig. figs?202105010,002
25Significant Figures Rules Leftmost zeroes are not significantHow many sig. figs?10002450.0031.01
26Homework 9/30 13) Error = -1.6°C, Percent error = 1.3% 14) a. unlimited b. 5 c d. 315) 6.6 x b. 4.0 x c d x e. 1.9 x 1014
27Significant Figures Rules Zeroes at the end of a number to the right of a decimal point are significantHow many sig. figs?1.000.01
28Zeroes at the end of a number are also significant if they are followed by a decimal point How many sig figs?1020010200.
29Significant Figures Rules Countable or standard measurements have infinite sig. figsHow many sig. figs?4 apples60 seconds/minute
30Significant Figures in Calculations In general, a calculated answer cannot be more precise than the least precise measurement from which it was calculated.
31Addition and Subtraction Round your answer to the largest digit that is the least significant digit of one of your measurementsExample: 12.52349.0369.76Answer = 369.7
32Multiplication and Division Round your answer to the same number of sig. figs as the term with the least number of sig. figs175 m x 0.1 m = 17.5 mAnswer = 20 m
34The Metric SystemThe metric system is an international system of units designed to make measurements simple and easyThe five metric units we’ll use in class areMetersGramsKelvinsSecondsMoles
35Meters and Seconds Meters (m) are the metric unit of distance 1 meter ≈ 3.3 feetSeconds (s) are the metric unit of time
36Grams Grams (g) are the metric unit of mass A paperclip weighs about 1 gram
37Kelvins A kelvin (K) is the metric degree of temperature 1 degree Kelvin = 1 degree CelsiusBUT the Kelvin scale starts at the lowest temperature possible, -273°CTo convert from Celsius to Kelvin, subtract 273.
38Moles A mole is the metric unit of quantity 1 mole = 6.02 x 1023 Very large, usually used for talking about how many atoms or molecules are in an object.
39Metric prefixesWe can use a standard set of prefixes to make the scale of metric units more convenientMega = 1 million times the unitKilo = 1 thousand times the unitHecto = 100 times the unitDeka = 10 times the unitDeci = 1/10 of the unitCenti = 1/100 of the unitMilli = 1/1000 of the unitMicro = 10-6 of the unitNano = 10-9 of the unitPico = of the unit
40VolumeVolume is the amount of space an object occupies. Volume = length x width x heightThe most common units we’ll use are a cubic centimeter (cm3) and a liter (L)A liter equals 1000 cm3
41Energy Energy is the capacity to do work or produce heat The Joule (J) is the metric unit of energy.The calorie is another (non-metric) unit of energy1 calorie = 4.18 Joules
42Homework 10/321) a. 1/1000 or b c. 1/10 or d. 1/100 or 10-222) m3, L, dL, cL, mL, μL23) 8.8 x 102 cm325) C = K – 27326) 443 K41) 1 hour/60 min b) 103mg/1g c) 103mL/1dm342) 1.48 x 107 micrograms b) 3.72 g c) 6.63 x 104 cm3
44Practice problems How many: Meters in a kilometer? Centigrams in a gram?Milliliters in a liter?Microkelvins in a kelvin?Joules in a Megajoule?Nanometers in a meter?Moles in a hectomole?
45Conversion ProblemsA quantity can usually be expressed in several different ways1 dollar = 4 quarters = 10 dimes = 20 nickelsThe same is true of scientific quantities1 meter = 10 decimeters = 100 centimetersHow do we convert from one unit to another?
46Conversion problems How do we convert from one unit to another? Conversion factorsA conversion factor is a ratio of equivalent measurements used to convert one unit to another.Example: 1 meter (m) = 100 centimeters (cm)Convert 2 m to cm2 m x 100 𝑐𝑚 1 𝑚 = 200 cm
47Conversion problems How do I choose a conversion factor? Find an equivalency between the unit your measurement is in and the unit you’re changing toSet up a ratio of equivalent measurementsPlace your desired unit on topConverting 760 grams to kilograms1000 g = 1 kg760 g x 1 𝑘𝑔 1000 𝑔 = 760 𝑘𝑔 = 0.76 kg
48Practice problems Convert using conversion factors: 750 milliliters to liters15 centimeters to meters1.5 decimeters to meters750 kilojoules to Megajoules5 nanograms to grams4.5 kilokelvins to centikelvins
49Dimensional AnalysisSolve the following problems with conversion factors:How many seconds are in 8 hours?How many inches are in a mile?How many Joules are in 200 calories?
50Density Use your intuition What is more dense, a bucket of pennies or a bucket of feathers?What is more dense, a block of wood or a block of iron?What does density mean?
51Density What is density? Density is the ratio of an object’s mass to it’s volumeDensity = 𝑚𝑎𝑠𝑠 𝑣𝑜𝑙𝑢𝑚𝑒Stated another way, density is a measure of how tightly matter is packed in an object
52Practice problemYou have four blocks of different elements. Use a ruler and a balance to calculate the density of each.
53BuoyancyDensity determines whether an object will sink or float in a fluid.More dense sinkLess dense floatIs wood more or less dense than water?Is a rock more or less dense than water?Is a person more or less dense than water?