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

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

Laboratory Measurements

• Evaluate physical and chemical environment – length, volume, mass, energy, and

temperature

• Good laboratory techniques are invaluable

Accuracy

• Closest to the true value– True value = 34.878

• Device measures–34.881–34.876–34.877

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• 25.45

– known = 25.4; estimated = 0.05

Examples

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)