Question

sodiul cu masa de 2.3g a reactionat cu apa.Calculeaza partea de masa a substantei in solutie daca volumul apei constituie 100ml

Answer 1

Na + HOH => NaOH + 1/2 H2

m Na=2.3 g => n Na = 0.1 mol (M Na= 23 g/mol)

V H2O= 100 ml = 100 g (densitate = m solutie/ V solutie)
d apa= 1 g/ml

1 mol Na ... 1 mol NaOH
0.1 mol Na ....x mol NaOH
x=0.1 mol NaOH => m NaOH = 0.1 mol x 40 g/mol =4 g NaOH
m solutie obtinuta = m H2O + m NaOH = 104 g
c=md/ms x100 => c= 4/104 x100 =3.84%