What happens if the spot line and positions are marked on the plate with a ballpoint pen when preparing a TLC plate for development? a. The spots will be difficult to see after development. b. Additional spots will appear on the plate, interfering with analysis. c. The spots will saturate the plate, show tailing, and/or diffuse into one another. d. The spot material will dissolve off the plate.

The higher the astm grain-size number, the coarser the grain is. a)-true b)-false

Asolid cylinder is concentric with a straight pipe. the cylinder is 0.5 m long and has an outside diameter of 8 cm. the pipe has an inside diameter of 8.5 cm. the annulus between the cylinder ad the pipe contains stationary oil. the oil has a specific gravity of 0.92 and a kinematic viscosity of 5.57 x 10-4 m2/s. most nearly, what is the force needed to move the cylinder along the pipe at a constant velocity of 1 m/s?

Ahe-xe mixture containing a 0.75 mole fraction of helium is used for cooling electronics in an avionics application. at a temperature of 300 k and atmospheric pressure, calculate the mass fraction of helium and the mass density, molar concentration and molecular weight of the mixture. if the cooling capacity is 10 l, what is the mass of the coolant?