[andyvidler]

Rittinger’s constant for a synthetic opiate material with a density of 1.32 g.cm–3 is 28 Jm–2. A ball mill with a power consumption quoted at 37.5 kWh/tonne is used to comminute this material from an initial particle size of approximately 2.5 mm. If the particles are milled for ten minutes, assuming Rittinger’s hypothesis applies, what will their average diameter be at the end of the process?

[andyvidler]

A researcher in Urumqi drops a rhodium ball of diameter 4.20 mm through a dilute aqueous solution of a high molar mass natural gum contained within a glass tube which has four graduations marked 10 cm apart. It is 18 C in the laboratory and the ball takes 1.86 seconds to fall between the first and second marks, 1.74 seconds to fall between the second and the third, and 1.74 seconds to fall between the third and the fourth. What is the viscosity of the liquid? What other information should be provided to allow you to answer the question more accurately?

[andyvidler]

In a sedimentation experiment using a centrifuge rotating at 20,000 rpm at 25°C the position of the boundary between the settled phase and the supernatant for a protein was found to be at 6.153 cm at t = 300 s, 6.179 at 600 s, and 6.206 at 900 s. If D for the protein is 7.62 × 10–11 m2s–1 at 20°C and it has a density of 1.373 g cm–3, what is its molecular weight?

[Borek]

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