Question

cat precipitat brun vor depune 4.2 g alchena daca la oxidarea cu permanganat de potasiu in med slab bazic sau neutru ii creste masa cu 48.57%?

Answer 1

CxH2x + [O] + H2O = CxH(2x+2)O2
2KMnO4 + H2O = 2KOH + 2MnO2↓ + 3[O]
alchena : CxH2x   Ma = 14x  na = 4,2/14x = 0,3/x moli
diol : Md = 14x + 34    md = 148,57/100 ·4,2 = 6,238  nd = 6,238/(14x + 34)
nd = na
6,238/(M+34) = 4,2/M    1,4854M = M + 34    0,4854M = 34   M = 7o g/mol
14x = 70        x = 5  alchena = C5H10
n alchena /nMnO2 = 3/2   nMnO2 = 2/3 ·0,3/5 = 0,04 moli    m = 0,04·87= 3,48g