3, A=p+n; 23=11+n---> n=12neutroni
1atom ..area...12 neutroni
1mol atomi......................12xN,A neutroni, unde N,A= 6,023X10²³
DECI in 23g............sunt........72,276x10²³ n
57,5g.............................x=180,66x10²³ n=18,066x10²⁴ n
R: a,b
14. masa medie a unui amestec este data de
M,mediu= c1/100M1 +c2/100M2---> rezulta sistemul:
79,989= c1/100x 79 + c2/100x 81
(c1+c2)/100= 1 --> rezolva sistemul si afli c1 si c2
