1 / 24

Chapter 2 Standards of Measurement

Chapter 2 Standards of Measurement. Objectives: Understand Mass and Weight (2.1) Identify the metric units of measurement (2.6) Explain what causes uncertainty in measurements (2.7, 2.8 – 2.12) Learn how to use significant digits and scientific notation (2.2 – 2.5) Dimensional Analysis (2.8)

xia
Download Presentation

Chapter 2 Standards of Measurement

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 2Standards of Measurement Objectives: • Understand Mass and Weight (2.1) • Identify the metric units of measurement (2.6) • Explain what causes uncertainty in measurements (2.7, 2.8 – 2.12) • Learn how to use significant digits and scientific notation (2.2 – 2.5) • Dimensional Analysis (2.8) • Density (2.12)

  2. The Metric System (2.6)The International System of Units • Standards of measurement • Base units (7) – see Table 2.2 (pg 20) • MASS: kilogram (kg) • LENGTH: meter (m) • TIME: second (s) • COUNT, QUANTITY: mole (mol) • TEMPERATURE: Kelvin (K) • ELECTRIC CURRENT: ampere (A) • LUMINOUS INSTENSITY: candela (cd)

  3. The Metric System • Derived Units: • AREA: square meter, m2 • VOLUME: cubic meter, m3 • ENERGY: joule, J • FORCE: newton, N • PRESSURE:pascal, Pa • POWER: watt, W • VOLTAGE: volt, V • FREQUENCY: hertz, Hz • ELECTRIC CHARGE: coulomb, C

  4. The Metric System • Metric Prefixes – make base unit larger or smaller • Table 2.1 – must know bolded prefixes • Based on 10 • Math method vs. “Stairs”

  5. Conversion Practice • Convert a volume of 12 microliters into centiliters • Express a distance of 15 meters in kilometers • Convert 83 cm into meters • Which is the longer amount of time, 1351 ps or 1.2 ns? • Convert 16 dL into L Answer: 0.0012 cL Answer: 0.015 km Answer: 0.83 m Answer: 1351 ps (1.2 ns = 1200 ns) Answer: 1.6 L

  6. Uncertainty in Measurement • Why are digits in measurements uncertain? • Instruments never completely free of flaws • Always involves estimation • Choose the right instrument for the job • May be estimated for you (electronic scales) • Scale is marked but you estimate the in-between

  7. Uncertainty in Measurement • Precision: getting the same result again and again under same conditions • Accuracy: close to accepted value

  8. Significant Digits • All digits known with certainty plus one final digit which is uncertain (or estimated) • All non-zeros are significant (143.34) • A zero is significant when : • It is between nonzero digits (2004) • It is at the end of a number that includes a decimal point (23.560) • A zero is not significant when: • It is before the first nonzero digit (0.25) • It is at the end of a number without a decimal point (2500)

  9. Significant Digits - PRACTICE How many significant digits? • 54.23 • 23.00005 • 0.0004 • 35000 • 0.000504 • 45.623200 • 5,000,000 • 4,000,000.1 • ANSWERS: • 4 sig figs • 7 • 1 • 2 • 3 • 8 • 1 • 8

  10. Significant Digits - Calculations • Addition and Subtraction • Round answer to have final digit in the SAME PLACE as the last digit in the LEAST ACCURATE MEASUREMENT • 1.21 + 5.002 + 10. = 16.212 becomes 16 • 34.5 + 12.45 + 23.0505 = • 186.31 + 11.1 = • 12.0231 + 3.86 = • 0.100012 + 120. = • 1200 + 12 + 15 + 0.5 = 70.0005 becomes 70.0 197.41 becomes 197.4 15.8831 becomes 15.88 120.100012 becomes 120. 1227.5 becomes 1200

  11. Significant Digits - Calculations • Multiplication and Division • The answer has as many sig figs as the number with the fewest sig figs • 14.8 x 3.1 = 45.88 becomes 46 • 18.2 x 3.0 = • 52/1.5 = • 321.868783 x 1 = • 2400 x 2.123 = • 15000/12.354 = 54.6 becomes 55 34.66666 becomes 35 321.868783 becomes 300 5095.2 becomes 5100 1214.181641 becomes 1200

  12. Scientific Notation • Convenient way of writing very large or very small numbers and showing only significant figures • Number between 1 & 10 with a power of ten • 5120 becomes 5.12 x 103 • Move decimal point in original number to make number 1-10 • Move left = +; move right = -

  13. Scientific Notation Practice 1.23 x 105 • 123,000 = • 0.000045 = • 23.45 = • 0.0000000003 = • 1,000,000 = 4.5 x 10-5 2.345 x 101 3 x 10-10 1 x 106

  14. Scientific Notation • Adding and subtracting • Numbers must be the SAME POWER • 1.4 x 104 + 2.1 x 105 (must change to 21.0 x 104) and then = 2.24 x 104 • 3.2 x 103 + 1.8 x 102 = 3.38 x 103

  15. Scientific Notation • Multiplying • Add exponents • (2.0 x 103) x (3.0 x 104) = 6.0 x 107 • Dividing • Subtract exponents • (8.2 x 108) x (4.1 x 104) = 2.0 x 104

  16. Types of Measurements • Mass – amount of matter in a body • Expressed in grams, kilograms, etc. • Does not change • Weight – measure of earth’s gravitational attraction for that object • Expressed in same units • Changes with location (position on earth or distance from earth)

  17. Types of Measurements • Volume – the amount of space occupied by matter • Cubic meter or liter • Many instruments to measure • Temperature – measure of the intensity of heat (figure 2.6) • Kelvin • Degrees Celsius • Degress Farenheit

  18. Conversion Factors • Enable movement between metric system and “English” system • See back cover of book and Appendix III • Common conversions you should memorize • 1 inch = 2.54 cm • 1 mile = 1.609 km • 1 kg = 2.20 pounds • 1 mL = 1 cm3 • 0 K = -273.15 0C • 0F = 1.8(0C) + 32

  19. Dimensional Analysis(Problem Solving) • Remember: ALWAYS use UNITS OF MEASUREMENT in your work!!! • A technique of converting between units • Same system (metrics) • Different systems (inches to meters) • Chemical equations….later chapters…

  20. Dimensional Analysis(Problem Solving) • Conversion Factors: ratio derived from the equality between 2 different units 3 feet = 1 1 dollar = 1 1 yard 4 quarters • CF can be written either way 1 minute = 1 60 seconds = 1 60 seconds 1 minute

  21. The “t” method Dimensional Analysis(Problem Solving) unit given unit wanted = unit wanted unit given Conversion Factor Example: How many liters are in 125.6 gallons? 125.6 gallons 3.785 Liters = 1 gallon 475.4 L

  22. Dimensional Analysis(Problem Solving) Dimensional Analysis(Problem Solving) How many seconds are in 4.15 hours? 4.15 hours 60 minutes 60 seconds = 1 hour 1 minute 14900 s If a student needs 1.5 mL of water, how many cups does he need? 1.5 mL 1 L 1 gal 4 qts 4 cups = 1000 mL 3.785 L 1 gal 1 qt 0.0063 cups

  23. Common ratio used in chemistry Physical property of a substance Mass/volume D = m v SI units: kg/m3 Solid g/cm3 Liquid g/mL Gas g/L Density Can change due to temperature and/or pressure changes

  24. Density • Find the density of a piece of metal with a volume of 2.7 cm3 and a mass of 10.8 g. • D = m • v = 10.8 g 2.7 cm3 = 4.0 g/cm3 2. Determine the mass of an object with a density of 0.24 g/cm3 and a volume of 2 cm3. SIG FIGS!!! m = d x v = 0.24 g/cm3 x 2 cm3 = 0.48 0.5 g

More Related