Question

Un amestec de izobutena si 2,3-dimetil-2-butena, in raport molar de 2:5 se oxideaza cu KMnO4/H2SO4. Substanta organica obtinuta se dizolva in 52,2g H2O formand o solutie de concentratie 25%. Masa de izobutena din amestec este:
A. 4,8g
B. 4,2g
C. 2,9g
D. 1,4g
E. 2,8g

Answer 1

(CH3)2C=C(CH3)2 + 2 [O] (KMnO4 + H2SO4) => 2 CH3-CO-CH3 
(CH3)2C=CH2 + 4 [O] (KMnO4 + H2SO4) => CH3-CO-CH3 + CO2 + H2O
Substanta dizolvata este acetona.
c = md/ms * 100
ms = md + m apa = md + 52,2
25 = md/(md+52,2) * 100
100 md = 25md + 1305 => 75 md = 1305 => md = 17,4 g acetona
1 mol 2,3-dimetil-2-butena..........2*58 g acetona
x moli ..........................................a g acetona
a = 116x
1 mol izo-butena..........58 g acetona
y moli ............................b g acetona
b = 58y
a+b = 17.4
x/y = 5/2 => 5y = 2x => x = 5y/2
116*(5y/2) + 58y = 17.4
=> 290y + 58y = 17.4 => y = 0.05 moli izobutena
masa de izobutena = 0.05* 56 = 2.8 g