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

Safety Put on Goggles And Apron

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

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)

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

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

Laboratory Measurements Metric system uses base 10 for measurements and conversions Conversions are done by multiplying or dividing by 10 7

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

Accuracy Closest to the true value True value = 34.878 Device measures 34.881 34.876 34.877 9

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

Precision and Accuracy

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

Examples 13

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

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

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

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

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

Conversion Table

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

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

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

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)