Measurements, Quantities, and Unity Factors Lecture Demonstrations - ChemPRIME

Measurements, Quantities, and Unity Factors Lecture Demonstrations

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Contents

Volume, Mass, and Density of a Bowling Ball and Similarly Sized Balloon filled with H2

Convert Mass

Convert 12 lb weight of bowling ball to g, showing unity factors

12.00 lb x 453.59237 g/lb = 5443 g

Calculate and convert volumes

V=4/3 π r3

V = 4/3 * 3.1416 * (1/2 * 8.59 in)3 =

4/3 * 3.1416 * 79.23 in3

=331.9 in3

Unity Factor: 2.54 cm = 1 in

331.9 in3 x (2.54 cm / 1 in)3 Note!!!

331.9 in3 x 16.39cm3/in3

= 5439 cm3

Densities

Will the bowling ball float in water? Demo [1]

D = 5443 g / 5439 cm3 Too close to call. See Errors in Measurement Lecture Demonstrations

Mass vs. Weight

What is the mass of hydrogen?

Density of hydrogen at room temperature and 1 Atm = 0.082 g/L

What is the volume in L, assuming same size as bowling ball? Unity Factors?

1 cm3 = 1 mL = 10-3L (Note: 1 mL = 1 cm3 = “1 cc”)

V (L) = 5500 cm3 x (1 L / 1000 cm3)

m (g) = V (L) * D (g/L) = 5.500 L x 0.082 g/cm3

= 0.451 g

Why does the Hydrogen balloon float? F = W = m g

F = W = (0.451 g x 1 kg /1000g) * 9.8 m*s-2 =

= 0. 0044 N

Force Upward: (Archimedes)

D of air = 1.2 g /L; Archimedes Principle: buoyancy = mass of air displaced (6.6 g)

F = m g

F = ( 6.6 g x 1 kg /1000g) * 9.8 m*s-2 =

= 0. 065 N

Net force = 0.065 N - 0.044 N upwards.


References

  1. J. Chem. Educ., 2004, 81 (9), p 1309
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