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Peste 400g solutie NaOH se adauga 200g apa. Concentratia solutiei devine 20%. Care este concentratia procentuala a solutiei initiale??

Răspuns :

Calculam masa de NaOH dizolvata in solutie
cf/100=md/msf => md=cf*msf/100=20*400/100=80g NaOH
msf=ms+mapa => ms=400-200=200g solutie
c=md*100/ms=80*100/200=40%