Răspuns:
v,apa=10x10³ l
1 l apa contine 30gNaCl
10x10³l.......................x
x=3x10⁵gNaCl
1mol NaCl contine 1 mol ioni clor...........6,023x10 ioni
x..........................................................................12,046x10²³ioni
x=n=2mol NaCl
xplicație: