Question
What are the products of reaction Na2CO3 + C6H8O7 + H2O ?
Answer and explanation
When citric acid (C6H8O7) interacts with sodium bicarbonate (Na2CO3) in water solution, sodium citrates
and carbonic acid are formed. Carbonic acid spontaneously decomposes to water and carbon dioxide (CO2).
That is why gassing is observed.
Generally, brutto-reaction may be given as
Na2CO3 + C6H8O7 → C6H6O7Na2 + H2CO3
disodium citrate carbonic acid
or
Na2CO3 + C6H8O7 → C6H6O7Na2 + H2O + CO2
disodium citrate
carbon dioxide
(H2O is a solvent and it is not necessary to write it in the reaction scheme)
Given scheme, however, is only an example, one of possible alternatives.
O
O
OH
OH
CH 2 C CH 2
HO
HO
O
Citric acid (C6H8O7) is tribasic acid having the following structure
Since citric acid is tribasic, i.e. contains three carboxyl groups, three types of salts (sodium citrates) may
be formed: sodium citrate, disodium citrate and trisodium citrare. So, the exact composition of the reaction
products depends on the Na2CO3 / C6H8O7 ratio.
All possible alternatives are given in schemes below
Na2CO3/
C6H8O7
molar
ratio = 1:2
Na2CO3/
C6H8O7
molar
ratio = 1:1
Na2CO3/
C6H8O7
molar
ratio = 3:2
Na2CO3/
C6H8O7
molar
ratio = 2:1
O
HO
HO
+
CH 2
2
O
O
OH
OH
C CH 2
HO
CH 2
2
Na 2CO 3
O
OH
OH
C CH 2
+
NaO
O
CO 2
H2CO 3
(1)
O
H2O
sodium citrate
O
HO
CH 2
O
O
OH
OH
C CH2
HO
+
HO
CH 2
Na 2CO 3
O
OH
ONa
C CH2
+
NaO
O
CO 2
H2CO 3
(2)
O
H2O
disodium citrate
O
O
O
OH
OH
CH2 C CH2
HO
NaO
+
2
HO
3
2
Na2CO 3
O
OH
ONa
CH2 C CH2
+
NaO
O
3 CO2
3
H2CO 3
(3)
O
3 H2O
trisodium citrate
O
HO
O
O
OH
OH
CH2 C CH2
+
HO
O
NaO
2
Na2CO 3
CH2
NaO
O
OH
ONa
C CH2
+
CO 2
NaHCO 3
+
H2CO 3
trisodium citrate
(4)
H2O
O
sodium hydrogen carbonate
In the first case (1) there is molar excess of citric acid.
In the second case (2) the reactants are taken in equimolar ratio.
In the third (3) and forth (4) cases there is molar excess of sodium bicarbonate.
In the forth case (4) sodium hydrogen carbonate is formed.
Actually, not only one but several of given reactions may occurs at the same time, and reaction products
mixture may include all three types of citrates. However, some of the possible reactions and some of the
citrates considerably prevail over other alternatives, depending on the reactants ratio.
Answer: sodium citrate (C6H7O7Na), disodium citrate (C6H6O7Na2), trisodium citrare (C6H5O7Na3), water
(H2O), carbon dioxide (CO2), carbonic acid (H2CO3), sodium hydrogen carbonate (NaHCO3).