Question

III. Calculează masa de apă ce trebuie adăugată peste 200 g soluţie de clorura de sodiu 20% pentru a obţine o soluţie de concentraţie 10% (folosiţi regula dreptunghiului).

Answer 1

ms1=200g                                                                                                             c1=20                                                                                                                        c2=10                                                                                                                            mapa adaugata
c1=md .100:ms1                                                                                      md=c1.ms1:100                                                                                             md=20.200:100=40g NaCl
Acest md este si pentru a doua solutie.Se calculeaza masa apei din prima solutie                                                                                                                            ms1=md +mapa                                                                                                             mapa = ms1-md                                                                                                 mapa=200-40=160 g apa                                                                                                Trecem la  a doua  solutie                                                                                                        c2=md.100:ms2                                                                      ms2=md.100:c2                                                                                                          ms2=40.100:10=400 g sol                                                                                            .ms2=md +mapa                                                                                                          mapa =ms2- md                                                                                                   mapa=400-40=360 g apa in total                                                                              360-160=200 g care se va adauga