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Measurements and Calculations

Measurements and Calculations. Chapter 2. Suggested Problem Set: Page 59 #4, 8-13, 16-18, 21-23, 27-30, 32-34, 37-45 Chapter 2 Quizzes: Monday, Wednesday Unit 1 Test: Friday, August 27. SI Measurement. Le Systeme International d’ Unites (SI) All measurements consist of 2 parts

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Measurements and Calculations

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  1. Measurements and Calculations Chapter 2 Suggested Problem Set: Page 59 #4, 8-13, 16-18, 21-23, 27-30, 32-34, 37-45 Chapter 2 Quizzes: Monday, Wednesday Unit 1 Test: Friday, August 27

  2. SI Measurement • Le Systeme International d’ Unites (SI) • All measurements consist of 2 parts • A number and unit • i.e. 15 g, 25 m, 1.2 mol

  3. SI Measurement cont… • SI Base Units • Length • Mass • Time • Temperature • Amount of a Substance

  4. SI Measurement cont… • Derived Units • Units that are derived from 2 or more base units in combination with one another • i.e. Volume, Density, Velocity, Molar mass, Concentration, Area, etc.

  5. SI Measurement cont… • Prefixes: • kilo • deci • centi • milli • micro • nano • pico

  6. iClicker Question • What does the prefix giga stand for? • 103 • 106 • 109 • 1012 • 1015

  7. Density • Density is an important property of matter that is often used to identify a substance • It is the ratio of the mass of an object to its volume • The density of an object is usually compared to water which has a density of 1.0 g / ml.

  8. iClicker Question • If the unit for mass is grams and the unit for volume is cm3, what would density be measure in? • grams • cm3 • g-cm3 • g/cm3 • g/ml

  9. Sample Problem • What is the density of a sample of ore that has a mass of 74.0 g and occupies 20.3 cm3?

  10. Sample Problem What is the volume of a sample of wood that has a mass of 95.1g and a density of 0.857 g/cm3?

  11. Density Quick Lab Thickness of Aluminum Foil

  12. Conversion Factors • Are used to convert from one unit of measure to another • They start with equalities • 12 inches = 1foot • 5280 feet = 1 mile • 1 mile = 1.61 km • 1 inch = 2.54 cm • Conversion factors are usually just a different way of writing the number 1

  13. Sample Problem • How many km/min is a car going if it is traveling at 65 miles/hr?

  14. Sample Problem • How many cm3 are there in 15 in3?

  15. iClicker Question • If there are 1600m in a mile, how many miles is 2000km? • 0.0008 • 1.3 • 1250 • 3200 • None of the above is correct

  16. Scientific Measurement • Accuracy • the closeness to the true value of a measure. • Precision • a measure of the reproducibility of a measurement • You can be precise in a series of measurements and not accurate, but if you are accurate in a series of measures, you are also precise

  17. Percent Error • Percent error is used often in the laboratory setting to determine how close your experimental results are to the actual true value that they should be. • It is calculate using the following formula

  18. Significant Figures • Significant figures are the numbers we actually count in a calculation • First we must learn how to count them, then do calculations with them, and finally report answers to the correct number of significant figures

  19. Rules for counting significant figures • All non-zero numbers (1-9) are significant • Zeros • There are 3 types • Preceding (example – 0.00235) • Middle (example – 2002.01) • Trailing (examples – 100.0, 100)

  20. iClicker Question • Which of the following has 3 significant figures? • 0.003 • 320 • 1001.1 • 4.0031 • 901.0

  21. Calculations with Significant Figures • Multiplication and division rule • Report your answer to the same number of significant figures as the number in the problem with the fewest significant figures • Addition and subtraction rule • Report your answer to the same column as the number in the problem with the least precision

  22. Sample Problems • Find the volume of a cube that is 3.23 cm on each edge.

  23. iClicker Question • What is the sum of 67.14 kg and 8.2 kg? • 75 kg • 75.3 kg • 75.30 kg • 75.34 kg • 75.4 kg

  24. Sample Problem • Calculate the density of a 17.982 g object that occupies 4.13 cm3

  25. Scientific Notation • Numbers are written in the form: • M x 10n • Where M = any number >1 but < 10 • 1.25, 9.8, 2

  26. iClicker Question • Which of the following is not correctly written in scientific notation? • 1.00 x 104 • 1.1 x 10-3 • 0.9 x 109 • 7 x 101 • 2.0 x 1015

  27. Direct Proportions • Directly Proportional • Two quantities are directly proportional if dividing them gives a constant value • i.e. Density • This means whatever one variable does the other variable will do exactly the same • Graphically this will result in a straight line

  28. Inverse Proportions • Inversely Proportional • Two quantities are inversely proportional to one another if their product is equal to a constant • If one goes up the other will go down by a corresponding amount • Graphically this will result in a hyperbola

  29. End of Chapter 2 Suggested Problem Set: Page 59 #4, 8-13, 16-18, 21-23, 27-30, 32-34, 37-45 Chapter 2 Quizzes: Monday, Wednesday Unit 1 Test: Friday, August 27

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