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Ch. 1: Measurements

Ch. 1: Measurements. Chem 20-1204 El Camino College. Units. Units of Length meter (m), centimeter (cm), inch (in.) 1 m = 100 cm 1 m = 39.4 in. 2.54 cm = 1 in. Ex. Which is larger, a meter or a cm?. a meter. a meter. Ex. Which is larger, an in. or a meter?. Units. Units of Volume

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Ch. 1: Measurements

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  1. Ch. 1: Measurements Chem 20-1204 El Camino College

  2. Units • Units of Length • meter (m), centimeter (cm), inch (in.) • 1 m = 100 cm • 1 m = 39.4 in. • 2.54 cm = 1 in. Ex. Which is larger, a meter or a cm? a meter a meter. Ex. Which is larger, an in. or a meter?

  3. Units • Units of Volume • liter (L), milliliter (mL), quart (qt) • 1 L = 1000 mL • 1 L = 1.06 qt • 946 mL = 1 qt Ex. Which is larger, a milliliter or a liter? a liter a liter. Ex. Which is larger, a quart or a liter?

  4. Units • Units of Mass • gram (g), kilogram (kg), pound (lb) • 1 kg = 1000 g • 1 kg = 2.20 lb • 454 g = 1 lb Ex. Which is larger, a g or a kg? a kg Ex. Do you weigh a higher number of pounds or kilograms? lbs

  5. Units • Units of Temperature • Fahrenheit (oF), Celsius (oC), Kelvin (K) • freezing pt of H2O is 32 oF, 0 oC, 273 K • boiling pt of H2O is 212 oF, 100 oC, 373 K Ex. What is being measured: length, volume, mass, or temp? 292 K 23 mL 0.004 cm. temp volume length

  6. For Very Large or Small Numbers • Scientific notation has a specific form • a.bcd x 10e • a.bc (the number must be ³1 to <10) • 10e (the e is the exponent) x 101 = x 10 x 102 = x 100 x 103 = x1000 x 10-1 = x .1 x 10-2 = x .01 x 10-3 = x .001

  7. Solved Examples • Write 53 in scientific notation • Convert to a.bc form (between 1 and 10) • 5.3 • To go from the a.bc form to 53, the decimal moves 1 place to the right • 5.3 x 101

  8. Solved Examples • Write 8769 in scientific notation • Convert to a.bc form (between 1 and 10) • 8.769 • To go from the a.bc form to 8769, the decimal moves 3 places to the right • 8.769 x 103

  9. Solved Examples • Write 100.30 in scientific notation • Convert to a.bc form (between 1 and 10) • 1.0030 • To go from the a.bc form to 100.30, the decimal moves 2 places to the right • 1.0030 x 102

  10. Solved Examples • Write 0.00367 in scientific notation • Convert to a.bc form (between 1 and 10) • 3.67 • To go from the a.bc form to 0.00367, the decimal moves 3 places to the left • 3.67 x 10-3

  11. Examples • Write these in scientific notation • 501 = • 3,256,000 = • 0.042 = • 0.0005395 = 5.01 x 102 3.256 x 106 4.2 x 10-2 5.395 x 10-4

  12. Solved Examples • Write 1.0389 x 102 in decimal form • 1.0389 x 102 means that the decimal moves 2 places to the right • 103.89 • Write 8.0 x 10-3 in decimal form • 8.0 x 10-3 means that the decimal moves 3 places to the left • .0080

  13. Examples • Write these in decimal notation • 3 x 100 = • 6.022 x 104 = • 5.33 x 10-3 = • 9.99 x 101 = 3 60220 0.00533 99.9

  14. 5.62 x 10-3 = 6.36 x 10-8 8.84 x 104 On Your Calculator • Don’t use the 10x key • Don’t press “x 10” • You must use the EE or EXP key • 5.62 x 10-3 is 5.62 exp 3 +/- • Try this calculation. If you get a different result, see me after class

  15. Place Names ___ ___ ___ . ___ ___ ___ hundreds tens ones tenths thousandths hundredths

  16. 60 min 1 hr Dimensional Analysis • How many minutes are in 2.0 hrs? • The 2.0 hrs is your given information • The conversion (60 min/1 hr) is called a conversion factor • Always start with the given information • Write the conversion factor so the units to be cancelled are on the bottom. 2.0 hrs = 120 min

  17. 1 min 60 sec 1 hr 60 min Dimensional Analysis • How many minutes in 936.2 sec? 936.2 sec = 15.60 min • How many hrs in 53 min? 53 min = 0.88 hr

  18. 1 min 60 sec 1 hour 60 min Dimensional Analysis • If you need two conversions, don’t stop in the middle. Write one conversion after the other. • Hit the times (X) key between numerators • Hit the divide (/) key between denominators • How many hours in 9365 sec? 9365 sec = 2.601 hr

  19. 1 min 60 sec 24 hrs 1 day 1 hour 60 min 60 min 1 hr Dimensional Analysis • How many hrs in 5,877 sec? 5,877 sec = 1.633 hr • How many minutes in 0.052 days? 0.052 days = 75 min

  20. Metric Prefixes to Memorize prefixsymbolmultiple kilo k 1000 g / 1 kg centi c 1 m / 100 cm milli m 1 L / 1000 mL micro m 1 g / 1 x 106mg nano n 1 m / 1 x 109 nm also useful is 1 cm = 10 mm

  21. 1 cm .01 m 1 x 102 cm 1 m 1 m 100 cm 100 cm 1 m Metric Conversion Factors • There are many ways to write conversion factors • Make sure you know which unit is bigger • Many small units = one big unit • A fraction of a big unit = one small unit

  22. 54.8 g = 0.0548 kg 100 cm 1 m 1 kg 1000 g Examples: Use Dimensional Analysis • Always put the number by itself before the conversion factor • How many cm in 4.6 m? = 460 cm 4.6 m How many kg in 54.8 g?

  23. 1 kL 1000 L 1 x 106mm 1 m 1 g 1000 mg 1 kg 1000 g Examples • How many kL in 4,329,647 L? = 4329.647 kL 4,329,647 L • How many mm in 0.33 m? 0.33 m = 3.3 x 105mm • How many kg in 828 mg? 828 mg = 8.28 x 10-4 kg

  24. English Units • These are the most common US units • mass: ounce, pound • length: inch, foot, yard • volume: cubic inch, fl. oz., gallon

  25. 1 lb = 454 g 1 oz = 28.3 g 2.20 lb = 1 kg 1 in. º 2.54 cm 39.4 in. = 1 m 0.621 mi = 1 km 1.06 qt = 1 L 1 qt = 946 mL Metric-US Conversions: Don’t Memorize

  26. 1 L 1.06 qt 2.81 L = 500.0 g 1 oz 28.3 g 17.7 oz = 8.994 in. 2.54 cm 1 in. 22.84 cm = Examples • How many liters are in 2.98 quarts? 2.98 qt • How many ounces are in 500.0 g? • How many cm in 8.994 in.?

  27. Place Names ___ ___ ___ . ___ ___ ___ hundreds tens ones tenths thousandths hundredths

  28. Significant Figures • Sig figs apply to measured amounts • Sig figs don’t apply to counted things

  29. Significant Figures • For any apparatus, read 1 place past the smallest mark • The last significant digit is estimated (the doubtful digit).

  30. 50o 40o 30o 20o 10o 0 oC Significant Figures 28 oC • The smallest mark is in the tens place • One place past the smallest mark is the ones.

  31. Ex. Read These 3.6 oC 110 oC 4.7 oC 5.5 oC meas-4

  32. Right on the Line? • Always read to one place past the smallest mark • Always read a piece of equipment to the same place. • Note: Read the meniscus (the bottom of the belly for water)

  33. Right on the Line? 3.0 mL

  34. Conversion Factors in Problems • Read the problem carefully, then write a conversion factor • When solving, write a number by itself first, then write the conversion factor

  35. 1 hour 65.9 miles 65.9 miles 65.9 miles 1 hour 1 hour = 876 miles Example • A car is traveling 65.9 miles per hour. How many miles will it go in 13.3 hrs? The conversion factor is or 13.3 hrs

  36. 1 min 1 sec 1 hr 38.8 mi 4.2 gal 60 sec = = 1.31 hr 13 min 51.0 mi • A car is traveling 38.8 miles per hour. How many hrs will it take to go 51.0 miles? • A pool empties at 4.2 gal per sec. How many min will it take to empty 3200 gal? 3200 gal

  37. m v 5.8 g = 1.5 g/mL 3.8 mL Density • Density is mass/volume D = Find the density of 3.8 mL of liquid that has a mass of 5.8 g. • Note: 1 mL º 1 cm3º 1 cc

  38. 19.3 g cm3 87.3 cm3 = 1685 g 0.53 g 1 cm3 19.3 g = 0.027 cm3 • The density of gold is 19.3 g/cm3. Find the mass of 87.3 cm3 of gold. • Find the volume of 0.53 g of gold using the density of 19.3 g/cm3.

  39. Density and Solids • The mass of a solid is measured on a balance or scale • The volume of a solid may be measured by volume displacement • Measure the vol of water in a cylinder • Add the solid • Measure the vol of water again • Vfinal - Vinitial = Vsolid

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