scientific measurement. measurements quantities with both a number and a unit – used to measure a...
TRANSCRIPT
![Page 1: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/1.jpg)
Scientific Measurement
![Page 2: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/2.jpg)
Measurements
• Quantities with both a number and a unit– Used to measure a physical property– .5 grams• Mass
– 2 liters• Volume
– 1.6 meters • Length
![Page 3: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/3.jpg)
Why 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.
![Page 4: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/4.jpg)
Scientific Notation
• In chemistry, we deal with numbers that are very big and very small– How many water molecules are in the beaker?• 600,000,000,000,000,000,000,000
– What is the width of a water molecule?• .0000000005 meters
![Page 5: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/5.jpg)
Scientific Notation• How can we express big and small numbers in
a simpler way? – Powers of 10• 10 = 101 1 = 100 • 100 = 102 0.1 = 10-1
• 1000 = 103 0.01 = 10-2
• 10,000 = 104 0.001 = 10-3
– Exponent = # of places you move the decimal point to get behind the first digit• Left = positive• Right = negative
![Page 6: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/6.jpg)
Scientific notation
![Page 7: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/7.jpg)
Practice problem
• Express the following numbers in exponential form:– 100,000– 100– 0.001– .1– 1
![Page 8: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/8.jpg)
Scientific notation
• To put a number in scientific notation, express it as the product of– A number between 1 and 10– A 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
![Page 9: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/9.jpg)
Practice problems
• Express the following numbers in scientific notation: – 5280 feet– 0.00042 grams– 602,000,000,000,000,000,000,000 atoms
![Page 10: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/10.jpg)
Accuracy v. Precision
• Accuracy = how close your measurements are to the correct value– Ex: I can run a mile in 7 minutes• If you measure my mile time and get 7 minutes, you are
highly accurate• If you measure my time and get 8 minutes you are
inaccurate
![Page 11: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/11.jpg)
Precision
• Precision = how close your measurements are to each other– If you measure my mile time and get 7 minutes
three times, you are very precise– If you measure my mile time and get 8 minutes
three times, you are still very precise• But you are not very accurate.
![Page 12: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/12.jpg)
Accuracy v. Precision
![Page 13: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/13.jpg)
Error
• Error is the difference between your measurement and the accepted value
Error = experimental value – accepted value
![Page 14: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/14.jpg)
Practice problem
• Calculate the error:– Experimental value = 1 meter• Accepted value = 1.02 meters
– Experimental value = 10.7 seconds• Accepted value = 10.5 seconds
![Page 15: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/15.jpg)
Percent 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?
![Page 16: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/16.jpg)
Percent error
• Percent error is an expression of error as a percentage of the accepted value
x 100%
![Page 17: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/17.jpg)
Percent 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.– What is the error? What is the percent error?
![Page 18: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/18.jpg)
Percent 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?
![Page 19: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/19.jpg)
Significant Figures
• The accuracy of our measurements is limited by the accuracy of our tools
• What’s the smallest increment marked on this scale?
![Page 20: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/20.jpg)
Significant Figures
• When 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
![Page 21: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/21.jpg)
Significant figures?
• Can I measure this length as 11.754325 cm?
• Why/why not?• How many significant figures should this
measurement have?
![Page 22: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/22.jpg)
Significant figure rules
• How do I know how many significant figures a given measurement has?– Example: I tell you I am 1.650 meters tall. How many
significant figures are there?• Rules: – All nonzero digits are significant– All zeroes between nonzero digits are significant– Leftmost zeroes are not significant– Rightmost zeroes are significant if they follow a
decimal point or are followed by a decimal point
![Page 23: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/23.jpg)
Significant Figures Rules
• All nonzero digits are significant– How many significant figures:– 220– 1000– 345
![Page 24: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/24.jpg)
Significant figure rules
• All zeroes between nonzero digits are significant– How many sig. figs?– 202– 1050– 10,002
![Page 25: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/25.jpg)
Significant Figures Rules
• Leftmost zeroes are not significant– How many sig. figs?– 100– 0245– 0.003– 1.01
![Page 26: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/26.jpg)
Homework 9/30
• 13) Error = -1.6°C, Percent error = 1.3%
• 14) a. unlimited b. 5 c. 3 d. 3
• 15) 6.6 x 104 b. 4.0 x 10-7 c. 107 d. 8.65 x 10-1 e. 1.9 x 1014
![Page 27: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/27.jpg)
Significant Figures Rules
• Zeroes at the end of a number to the right of a decimal point are significant– How many sig. figs?– 1.00– 0.01– 0.203400
![Page 28: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/28.jpg)
• Zeroes at the end of a number are also significant if they are followed by a decimal point– How many sig figs?– 10200– 10200.– 1030.00
![Page 29: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/29.jpg)
Significant Figures Rules
• Countable or standard measurements have infinite sig. figs– How many sig. figs? – 4 apples– 60 seconds/minute
![Page 30: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/30.jpg)
Significant Figures in Calculations
• In general, a calculated answer cannot be more precise than the least precise measurement from which it was calculated.
![Page 31: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/31.jpg)
Addition and Subtraction
• Round your answer to the largest digit that is the least significant digit of one of your measurements– Example: 12.52
349.0 + 8.24 369.76
Answer = 369.7
![Page 32: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/32.jpg)
Multiplication and Division
• Round your answer to the same number of sig. figs as the term with the least number of sig. figs
175 m x 0.1 m = 17.5 m
Answer = 20 m
![Page 33: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/33.jpg)
Practice problems
![Page 34: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/34.jpg)
The Metric System
• The metric system is an international system of units designed to make measurements simple and easy– The five metric units we’ll use in class are• Meters• Grams• Kelvins• Seconds• Moles
![Page 35: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/35.jpg)
Meters and Seconds
• Meters (m) are the metric unit of distance– 1 meter ≈ 3.3 feet
• Seconds (s) are the metric unit of time
![Page 36: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/36.jpg)
Grams
• Grams (g) are the metric unit of mass– A paperclip weighs about 1 gram
![Page 37: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/37.jpg)
Kelvins
• A kelvin (K) is the metric degree of temperature– 1 degree Kelvin = 1 degree Celsius– BUT the Kelvin scale starts at the lowest
temperature possible, -273°C– To convert from Celsius to Kelvin, subtract 273.
![Page 38: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/38.jpg)
Moles
• 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.
![Page 39: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/39.jpg)
Metric prefixes• We can use a standard set of prefixes to make the
scale of metric units more convenient – Mega = 1 million times the unit– Kilo = 1 thousand times the unit– Hecto = 100 times the unit– Deka = 10 times the unit– Deci = 1/10 of the unit– Centi = 1/100 of the unit– Milli = 1/1000 of the unit– Micro = 10-6 of the unit– Nano = 10-9 of the unit– Pico = 10-12 of the unit
![Page 40: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/40.jpg)
Volume
• Volume is the amount of space an object occupies. Volume = length x width x height
• The most common units we’ll use are a cubic centimeter (cm3) and a liter (L)– A liter equals 1000 cm3
![Page 41: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/41.jpg)
Energy
• 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 energy– 1 calorie = 4.18 Joules
![Page 42: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/42.jpg)
Homework 10/3
• 21) a. 1/1000 or 10-3 b. 10-9 c. 1/10 or 10-1 d. 1/100 or 10-2
• 22) m3, L, dL, cL, mL, μL• 23) 8.8 x 102 cm3
• 25) C = K – 273• 26) 443 K• 41) 1 hour/60 min b) 103mg/1g c) 103mL/1dm3
• 42) 1.48 x 107 micrograms b) 3.72 g c) 6.63 x 104 cm3
![Page 43: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/43.jpg)
![Page 44: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/44.jpg)
Practice 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?
![Page 45: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/45.jpg)
Conversion Problems
• A quantity can usually be expressed in several different ways– 1 dollar = 4 quarters = 10 dimes = 20 nickels
• The same is true of scientific quantities– 1 meter = 10 decimeters = 100 centimeters
• How do we convert from one unit to another?
![Page 46: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/46.jpg)
Conversion problems
• How do we convert from one unit to another?– Conversion factors
• A 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 = 200 cm
![Page 47: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/47.jpg)
Conversion problems
• How do I choose a conversion factor?– Find an equivalency between the unit your
measurement is in and the unit you’re changing to– Set up a ratio of equivalent measurements– Place your desired unit on top
Converting 760 grams to kilograms1000 g = 1 kg760 g x = = 0.76 kg
![Page 48: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/48.jpg)
Practice problems
• Convert using conversion factors:1) 750 milliliters to liters2) 15 centimeters to meters3) 1.5 decimeters to meters4) 750 kilojoules to Megajoules5) 5 nanograms to grams6) 4.5 kilokelvins to centikelvins
![Page 49: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/49.jpg)
Dimensional 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?
![Page 50: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/50.jpg)
Density
• 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?
![Page 51: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/51.jpg)
Density
• What is density?– Density is the ratio of an object’s mass to it’s
volume• Density =
– Stated another way, density is a measure of how tightly matter is packed in an object
![Page 52: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/52.jpg)
Practice problem
• You have four blocks of different elements. Use a ruler and a balance to calculate the density of each.
![Page 53: Scientific Measurement. Measurements Quantities with both a number and a unit – Used to measure a physical property –.5 grams Mass – 2 liters Volume –](https://reader035.vdocuments.net/reader035/viewer/2022062303/551aa718550346856e8b48b2/html5/thumbnails/53.jpg)
Buoyancy
• Density determines whether an object will sink or float in a fluid. – More dense sink– Less dense float
• Is 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?