Question

peste 100 grame solutie a unui acid monocarboxilic se adauga 20 grame KHCO3 pur (cantitatea se consuma in intregime),rezultand o solutie care contine 87,4 g apa (gazul rezultat se degaja in totalitate).Concentratia procentuala a solutiei de acid este?

Answer 1

CnH2nO2 + KHCO3 = CnH2n-1O2K + H2O + CO2
100 g KHCO3..........18 g H2O
20 g KHCO3...................x
x = 3,6 g H2O
c%=md/ms*100
ms = md + m apa => md = ms - m apa
m apa = 87.4 + 3.6 = 91 g apa
ms = md + m apa => md = 100-91 = 9 g acid
c%=md/ms*100 = 9/100*100 = 9%

Answer 2

R-COOH + KHCO3 ⇒ RCOOK + CO2↑ + H2O
initial : m acid + mH2O = 100g    mi H2O =100 - c·ms/100 = 100 - c
nKHCO3 = m/M = 20/100 = 0,2 moli
mf H2O = mi + 0,2·18 = 100 -  c + 3,6 = 87,4    c = 103,6 - 87,4 = 16,2%