21) a) 46g Na = 2moli Na (A Na = 23)
Stim ca un mol Na are (are 11 electroni in 1 atom) 11×6.023×10²³ atunci 2 moli vor avea 11×6.023×10²³×2=132,506 ×10²³ electroni.
b) 1 mol F2 are (9 electroni in 1 atom dar avem F2 deci luam 18/ molecula)
Vom avea pentru 2 moli: 2×18×6.023×10²³ =216,828 electroni.
c) 10 kg Ne = 10000g Ne (A Ne = 20g) = 10000/20 moli = 500 moli Ne
1 mol Ne (10 electroni are un atom) 10×6.023×10²³, atunci 500 moli vor fi
500×10×6.023×10²³ (scriu 500 ca 5×10²) = 5×10×6.023×10²⁵=301,15 × 10²⁵ electroni
22) a) 1 atom C are 12-6 = 6 neutroni/ atom
12g=1 mol C deci vom avea 6×6,023×10²³=36,128×10²³ neutroni
b) Hidrogenul nu are neutroni (1-1=0)
c) 2kg = 2000g O2 = 62,5 moli O2. Molecula de O2 are 2 atomi de O deci va avea de 2 ori mai multi neutroni. Un atom are 16-8=8 neutroni deci voi scrie direct 16 / molecula
16×62,5×6,023×10²³=6023×10²³=6,023×10²⁶ neutroni.
d) N are a atomi in molecula cu cate 14-7=7 neutroni fiecare. Scriu direct 14.
0.5 kmoli=500 moli
14×500×6,023×10²³(scriu 500=5×10²)=14×5×6,023×10²⁵=421,61×10²⁵ neutroni
