M = molar mass, n=moles, m=mass, Avogadro’s number = 6.022x10^23
1. m = n x M  n =? m = 24g, M=113 g/mol  n = m/M  n = 24/113 = n = 0.2 mol
2. M(Na2SO4) = 2 * A(Na) + A(S) + 4 * A(O) = 2 * 23 + 4 * (32 + 16) = 142 g/mol  n=m/M  n =
458/142 = 3.22 mol
3. How many grams are in 2.30 x 10^24 atoms of silver?  Ar(Ag) = 108 g/mol, m=?, atoms =
2.3x10^24  2.3x10^24 / 6.022x10^23 = 3.8 mol  n = 3.8 mol  m = n x M  m = 3.8 mol x
108 g/mol = 410.4 g
HNO3
%H
%N
%O
 Ml(HNO3) = 1 + 14 + 3x16 = 63
 %H = 1/63 * 100 = 1.5%
 %N = 14/63 * 100 = 22.2%
 %O = 3x16/63 * 100 = 76.19%
 = 1.5% + 22.2% + 76.19% = 99.99%