# Average diameters of colloids

by kasse
Tags: average, colloids, diameters
 P: 463 A dispersion of spherical polymer particles contains Np = 4•1013 particles/dm3. The total surface of the particles in 1 dm3 is Asp = 820 m2. a) What kind of average diameter can we calculate. Calculate this average diameter. b) If we know that the dispersion contains 60 vol% water, we can calculate another type of average diameter. Which? Find it! a) Surface average. $$\bar{d_s} = \sqrt{\frac{\Sigma n_i d_i^2}{\Sigma n_i}}$$ b) Volume average. $$\bar{d_s} = \sqrt{\frac{\Sigma n_i d_i^3}{\Sigma n_i}}$$ I don't know how to incorporate the data into the formulas.