The stannous fluoride in a 10.000 g sample of toothpaste was extracted and then precipitated
with lanthanum nitrate solution. if the mass of the precipitate is 0.105 g, what is the per-
centage of stannous fluoride in the toothpaste sample?
3 snf2 (aq) + 2 la(no3)3(aq) —>
laf3(s) + 3 sn(no3)2(aq)

answer: atomic mass was originally used to arrange elements on the periodic table, but is no longer used to organize the modern version.

explanation:

originally atomic mass was used to arrange elements on the periodic table from left to right in a row. each column then shows similar properties of elements of a group.

in modern periodic table, the atoms are arranged in increasing atomic number. as atomic number represents the number of protons in an atom which is unique for every atom.