3 mm = 0,3 cm
V sferă = 4/3*π*r^3 = 4/3 * 3,14 * (0,3)^3 = 0,113 cm3
ro = m/V
m = 0,113*1,74 = 0,196 g Mg
2 Mg + O2 = 2 MgO
M Mg = 24 g/mol
M MgO = 40 g/mol
V c.n. = 22,4 l
2*24 g Mg........22,4 l O2.......2*40 g MgO
0,196 g Mg..............x..................y
x = 0,0915 l O2
y = 0,326 g MgO
V aer = 100/20 * V O2 = 5*0,0915 = 0,4575 l aer = 457,5 ml aer