In: Chemistry
MgCl2 often occurs in table salt (NaCl) and is responsible for caking of the salt. A 0.5200 g sample of table salt is found to contain 61.10% Cl, by mass. What is the % MgCl2 in the sample? Why is the precision of this calculation so poor?
3.1% MgCl2; The precision of the calculation is poor because there is only a small % MgCl2 in the mixture. When calculating the number of moles of MgCl2, 0.5237 is subtracted from 0.5200 as shown above. The number of significant figures is reduced by this subtraction, which has the effect of reducing the precision in subsequent calculations.
Low precision due to small % MgCl2. Subtraction reduces significant figures, diminishing precision in further calculations.