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Published bySergio Frett Modified over 3 years ago

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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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Calculations Notes. Multiplication and Division Number of the sig. figs. is the result of the measurement with the smallest number of sig. figs. (least.

Calculations Notes. Multiplication and Division Number of the sig. figs. is the result of the measurement with the smallest number of sig. figs. (least.

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