Posted by **Simon** on Sunday, March 28, 2010 at 4:40am.

A column packing for chromatography consists of a mixture of two types of particles. Assume that the particles in the batch being sampled are spherical with a radius of 0.5 mm. 36% of the particles appeared to be pink and are known to have a polymeric stationary phase attached. The average density of the mixture is 0.288 g cm-3. If 5.3126„b0.0003 g of the sample is weighed out, calculate,

(i) the number of particles in the sample

(ii) the % standard deviation in sampling the fraction of pink particles from this mass of the sample.

(iii) Which contributes the larger uncertainty to the procedure - weighing out the sample or the random error associated with sampling from the two-component mixture? Justify your answer with a calculation.

(iv) Assume that the % standard deviation in sampling is 8%. How many replicate samples of this packing material need to be taken so that there is 95% confidence that the mean is known to within „b6% of the true mean.

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