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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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**CH4 (g) +2O2 (g) → CO2 (g) + 2H2O (g)**

Bunsen Burner Allows Controlled Mixture of Gas and Air Hottest Flame Nonluminous Violet outer cone Complete combustion occurs CH4 (g) +2O2 (g) → CO2 (g) + 2H2O (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 (SiO2) softens from ˚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 7

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**Laboratory Measurements**

Evaluate physical and chemical environment length, volume, mass, energy, and temperature Good laboratory techniques are invaluable 8

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**Accuracy Closest to the true value True value = 34.878 Device measures**

34.881 34.876 34.877 9

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**Precision Reproducibility of the measurement Little variability**

True value = 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 known = 25.4; estimated = 0.05

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Examples 13

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Division The Answer’s # of sig. fig. are same as number with the fewest digits being divided 12.3 ÷ = = 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 × = = 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 = = 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 – 3.63 = = 3.21

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Calculations Length: Record measurement to the nearest 16th 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 mm2

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**Calculations (Volume)**

Record Volume Convert using the conversion chart e.g., 48 mL × 1 L/1000 mL = 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 = 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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