Răspuns :
calculez masa de sare care se obtine, din ecuatia chimica
Zn + 2HCl ----> ZnCl2 + H2 unde M,Zn= 65g/mol M,ZnCl2= 136g/mol
65g......................136g
13g...................x=m=27,2g,,,,aceasta masa se dizolva
si aplic relatia c= mdx100/ms, unde md= 27,2g
ms= md+m,apa= 27,2+372,8--> 400g
c=27,2x100/400=....................calculeaza !!!