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## Measuring

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**Measuring**• Volume • Temperature • Mass • Distance**Reading the Meniscus**Always read volume from the bottom of the meniscus. The meniscus is the curved surface of a liquid in a narrow cylindrical container.**Try to avoid parallax errors.**Parallaxerrorsarise when a meniscus or needle is viewed from an angle rather than from straight-on at eye level. Incorrect: viewing the meniscusfrom an angle Correct: Viewing the meniscusat eye level**Graduated Cylinders**The glass cylinder has etched marks to indicate volumes, a pouring lip, and quite often, a plastic bumper to prevent breakage.**Measuring Volume**• Determine the volume contained in a graduated cylinder by reading the bottom of the meniscus at eye level. • Read the volume using all certaindigits and one uncertaindigit. • Certaindigits are determined from the calibration marks on the cylinder. • Theuncertaindigit (the last digit of the reading) is estimated.**Use the graduations to find all certain digits**There are two unlabeled graduations below the meniscus, and each graduation represents 1 mL, so the certain digits of the reading are… 52 mL.**Estimate the uncertain digit and take a reading**The meniscus is about eight tenths of the way to the next graduation, so the final digit in the reading is . 0.8 mL 52.8 mL. The volume in the graduated cylinder is**10 mL Graduate**What is the volume of liquid in the graduate? 6 6 2 _ . _ _ mL**25mL graduated cylinder**What is the volume of liquid in the graduate? 1 1 5 _ _ . _ mL**100mL graduated cylinder**What is the volume of liquid in the graduate? 5 2 7 _ _ . _ mL**Self Test**Examine the meniscus below and determine the volume of liquid contained in the graduated cylinder. The cylinder contains: 7 6 0 _ _ . _ mL**The Thermometer**• Determine the temperature by reading the scale on the thermometer at eye level. • Read the temperature by using all certaindigits and one uncertaindigit. • Certaindigits are determined from the calibration marks on the thermometer. • Theuncertaindigit (the last digit of the reading) is estimated. • On most thermometers encountered in a general chemistry lab, the tenths place is the uncertain digit.**Do not allow the tip to touch the walls or the bottom of the**flask. If the thermometer bulb touches the flask, the temperature of the glass will be measured instead of the temperature of the solution. Readings may be incorrect, particularly if the flask is on a hotplate or in an ice bath.**Reading the Thermometer**Determine the readings as shown below on Celsius thermometers: 8 7 4 3 5 0 _ _ . _ C _ _ . _ C**Measuring Mass– Electronic balance**Our balances read to the hundredths place,theuncertain digit is the hundredths place ( _ _ _ . _ X)**Balance Rules**In order to protect the balances and ensure accurate results, a number of rules should be followed: • Always check that the machine is zeroed before adding any substance on it. This is done by pushing the ZERO button before weighing any substance. • Never weigh directly on the balance pan. Always use a piece of weighing paper, weigh boat, or beaker to protect it. • Do not weigh hot or cold objects. • Clean up any spills around the balance immediately.**Determining Mass**• Place container (weigh boat or beaker) on the pan • Zero the balance by hitting the zero bottom • Place object on pan • Read the digits to the last digit**Metric Ruler**• Rulers are used to measure distance • Can be used to measure the volume of a cube (L x W x H) length x width x height • Determine the temperature by reading the scale on the thermometer at eye level. • Read the ruler by using all certaindigits and one uncertaindigit.**Reading a Ruler**• Determine the readings as shown below on centimeter ruler: _ _ . _ cm _ _ . _ cm**The Nature of Measurement**A Measurement is a quantitative observation consisting of TWO parts • Part 1-number • Part 2-scale (unit) • Examples: • 20grams • 6.63 x 10-34Joule·seconds**Metric Acronym**• K King • H Henry • D Died • M Monday • D Drinking • C Chocolate • M Milk**Metric Conversions**g m L 103 10-1 10-2 10-3 102 101 kilo hecto deka Base unit deci centi milli Conversions in the metric system are merely a matter of moving a decimal point. The “base unit” means the you have a quantity (grams, meters, Liters, etc without a prefix.**Metric Conversions**g m L 103 10-1 10-2 10-3 102 101 kilo hecto deka Base unit deci centi milli 1 2 3 18 L 18 liters = 18 000 milliliters Example #1: Convert 18 liters to milliliters**Metric Conversions**g m L 103 10-1 10-2 10-3 102 101 kilo hecto deka Base unit deci centi milli 3 2 1 450 mg = 0.450 g 450 mg Example #2: Convert 450 milligrams to grams**Metric Conversions Ladder Method**T. Trimpe 2008 http://sciencespot.net/**1**2 3 MetersLitersGrams How do you use the “ladder” method? 1st – Determine your starting point. 2nd – Count the “jumps” to your ending point. 3rd – Move the decimal the same number of jumps in the same direction. Starting Point Ending Point __. __. __. 2 3 1 Ladder Method KILO1000Units HECTO100Units DEKA10Units DECI0.1Unit CENTI0.01Unit MILLI0.001Unit 4 km = _________ m How many jumps does it take? 4. = 4000 m**Compare using <, >, or =.**56 cm 6 m 7 g 698 mg Conversion Practice Try these conversions using the ladder method. 1000 mg = _______ g 1 L = _______ mL 160 cm = _______ mm 14 km = _______ m 109 g = _______ kg 250 m = _______ km**Metric Conversion Challenge**Write the correct abbreviation for each metric unit. 1) Kilogram _____ 4) Milliliter _____ 7) Kilometer _____ 2) Meter _____ 5) Millimeter _____ 8) Centimeter _____ 3) Gram _____ 6) Liter _____ 9) Milligram _____ Try these conversions, using the ladder method. 10) 2000 mg = _______ g 15) 5 L = _______ mL 20) 16 cm = _______ mm 11) 104 km = _______ m 16) 198 g = _______ kg 21) 2500 m = _______ km 12) 480 cm = _____ m 17) 75 mL = _____ L 22) 65 g = _____ mg 13) 5.6 kg = _____ g 18) 50 cm = _____ m 23) 6.3 cm = _____ mm 14) 8 mm = _____ cm 19) 5.6 m = _____ cm 24) 120 mg = _____ g**Compare using <, >, or =.**25) 63 cm 6 m 27) 5 g 508 mg 29) 1,500 mL 1.5 L 26) 536 cm 53.6 dm 28) 43 mg 5 g 30) 3.6 m 36 cm**Problem #1**Convert400 mL to Liters L 400 mL 1 .400 L = 1 000 mL = 0.4 L = 4x10-1 L**Problem #2**Convert10 meters to mm mm 10 m 1 000 10 000 mm = 1 m = 1x104 mm**Problem #3**Convert73 grams to kg kg 73 g 1 0.073 kg = 1 000 g = 7.3x10-2 kg**Problem #4**Convert0.02 kilometers to m m 0.02 km 1 000 m 20 = 1 km = 2x101 m**Problem #5**Convert20 centimeters to m m 20 cm 1 m 0.20 = 100 cm = 2x10-1 m**Problem #6**Convert450 milliliters to dL dL 450 mL 1 4.5 dL = 100 mL**Problem #7**Convert10 kilograms to grams g 10 kg 1 000 10 000 g = 1 kg = 1x104 g**Problem #8**Convert935 mg to cg 1 cg 935 mg 93.5 cg = 10 mg = 9.35x101 cg**Problem #9**Convert5.2 kg to mg 5.2 kg 1 000 000 mg mg = 1 kg = 5 200 000 mg = 5.2x106 mg**Problem #10**Convert175 mL to cm3 cm3 1 175 mL 175 cm3 = 1 mL = 1.75x102 cm3**Uncertainty and Significant Figures**Cartoon courtesy of Lab-initio.com**Uncertainty in Measurement**• A digit that must be estimatedis called uncertain. Ameasurementalways has some degree of uncertainty.**Why Is there Uncertainty?**• Measurements are performed with instruments • No instrument can read to an infinite number of decimal places Which of these balances has the greatest uncertainty in measurement?