Modelová Otázka ID 2756 - 
Jaká je hmotnost 5 milionů molekul síranu železnatého? Ar(Fe) = 56; Ar(S) = 32
Správná odpověď je: A
Molární hmotnost FeSO4 je 152 g/mol. Vynásobením počtu molekul FeSO4 a Avogadrovy konstanty získáme látkové množství; hmotnost FeSO4 vypočítáme jako součin látkového množství a molární hmotnosti. Výpočet provedeme následovně:
m = n · M = (N/NA) · M = [(5 · 106)/(6,022 · 1023)] · 152
m = 1,262 · 10−15 g = 1,262 · 10−18 kg.
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