chem 1011 laboratory techniques: using the laboratory gas burner; making laboratory measurements
TRANSCRIPT
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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
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 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 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 = 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)