posted by smiley .
experiment: Gravimetric determination of moisture in fertilizer samples
1. What are the advantages of weighing by difference to direct weighing when using an analytical balance?
2. Why are the samples grinded before drying in the oven?
Weighing by difference minimizes errors in the balance, weights, and procedure. For example, suppose a 1 g weight actually had a mass of 2 grams. I know that won't happen but suppose it did. The mass you determine might be 1.500 but you would determine it as 2.500. Then suppose the next weighing is 2.5500 (actual mass is 1.550). Subracting 2.550 - 2.500 = 0.050 g and subtracting 1.550 - 1.500 = 0.05 g. That is you get the same answer although the mass of the weight was not correct. Solid samples are ground before drying in order to increase the surface area of the sample so that moisture is more readily driven out of the sample.