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CHEM 1011 Laboratory Techniques: Using the Laboratory Gas Burner; Making Laboratory Measurements

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Safety Put on Goggles And Apron

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Objectives Learn to use Bunsen burner Learn to use laboratory equipment Learn to take Measurements Record Measurements using the proper number of significant figures

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Bunsen Burner Allows Controlled Mixture of Gas and Air Hottest Flame –Nonluminous –Violet outer cone –Complete combustion occurs CH 4 (g) +2O 2 (g) → CO 2 (g) + 2H 2 O (g)

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Bunsen Burner Cooler Flame –Less Air –Luminous Yellow Flame –No Inner Cone –Smokey due to incomplete combustion

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Glassware Glassware in lab is a borosilicate glass –Consists of silica and borax –Does not soften much under 800˚C –Pyrex or Kimax –Low thermal Expansion coefficient Unlike soft Glass (SiO 2 ) – softens from 300-400˚C –High thermal Expansion coefficient

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Laboratory Measurements Metric system uses base 10 for measurements and conversions Conversions are done by multiplying or dividing by 10

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Laboratory Measurements Evaluate physical and chemical environment –length, volume, mass, energy, and temperature Good laboratory techniques are invaluable

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Accuracy Closest to the true value –True value = 34.878 Device measures –34.881 –34.876 –34.877

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Precision Reproducibility of the measurement Little variability –True value = 34.878 Device measures – 35.001 – 35.002 – 35.000

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Precision and Accuracy

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Significant Figures When measuring: –(1) uncertainty in last digit recorded 25.45 –(2) the # of significant figures contains all known #’s + one estimated 25.45 – known = 25.4; estimated = 0.05

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Examples

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Division The Answer’s # of sig. fig. are same as number with the fewest digits being divided 12.3 ÷ 6.235 = 1.972734563 = 1.97

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Multiplication The Answer’s # of sig. fig. are same as number with the fewest digits being multiplied 0.72 × 1.145 = 0.8244 = 0.82

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Addition The Answer’s # of sig. fig. are same as number with the fewest digits behind decimal being added 4.23 + 3.292 + 7.849 = 15.371 = 15.37

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Subtraction The Answer’s # of sig. fig. are same as number with the fewest digits behind decimal being subtracted 6.8384 – 3.63 = 3.2084 = 3.21

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Calculations Length: Record measurement to the nearest 16 th of an inch

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Conversion Table

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Calculations (Measurement) Record measurements Conversions can be made by dividing or multiplying by powers of 10 Ex. 34 cm × 10 mm/1 cm = 340 mm Area L × W (340 mm × 23 mm) = 8160 mm 2

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Calculations (Volume) Record Volume Convert using the conversion chart e.g., 48 mL × 1 L/1000 mL = 0.048 L Calculate percent error = (theoretical value – actual value)/ theoretical value × 100

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Calculations (Mass) Record values Convert from g to mg e.g., 15 g × 1000mg/1g = 15000 mg

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Calculations (Temperature) Record the Value in degrees Celsius Convert to Degrees Fahrenheit and Kelvin Degrees Fahrenheit use (9/5 (C) + 32 Degrees Kelvin use (C + 273)

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