When ethane - 1,2-dioic acid is heated with concentrated tetraoxosulphate (VI) acid, a reaction represented by the following equation occurs: (a) State the ...
Question 1 Report
When ethane - 1,2-dioic acid is heated with concentrated tetraoxosulphate (VI) acid, a reaction represented by the following equation occurs:
(a) State the type of process involved in the reaction
(b) What is the basicity of ethane-1, s-dioic acid?
(c) List three differences in the chemical properties of the two oxides of carbon produced during the reaction
Answer Details
The equation shown on the diagram is the action of hot concentrated tetraoxosulphate(VI) acid on ethanedioic (oxalic) acid:
\[ \underset{\text{(COOH)}_2}{\text{HOOC-COOH}} \;\xrightarrow[\;\Delta\;]{\text{conc. } H_2SO_4}\; CO_2 + CO + H_2O \]
(a) Type of process involved
The process is dehydration. The concentrated tetraoxosulphate(VI) acid acts as a dehydrating agent: it removes the elements of water (\(H_2O\)) from each mole of ethanedioic acid, leaving behind the two oxides of carbon, \(CO_2\) and \(CO\). Notice that the atoms balance exactly, \((COOH)_2 = C_2H_2O_4\) splits into \(CO_2 + CO + H_2O\), so no oxidation state change is imposed by the acid; it simply strips out water.
(b) Basicity of ethanedioic acid
The basicity of an acid is the number of replaceable (ionisable) hydrogen atoms it releases per molecule in aqueous solution. Ethanedioic acid, \((COOH)_2\), contains two carboxyl (-COOH) groups, each supplying one ionisable hydrogen:
\[ (COOH)_2 \rightleftharpoons 2H^+ + (COO)_2^{2-} \]
Therefore its basicity is 2 (it is a dibasic / diprotic acid).
(c) Three differences in the chemical properties of the two oxides of carbon (\(CO_2\) and \(CO\))
| Property | Carbon(IV) oxide, \(CO_2\) | Carbon(II) oxide, \(CO\) |
|---|---|---|
| Acid/base nature | Acidic oxide: turns moist blue litmus red and reacts with alkalis, e.g. \(CO_2 + 2NaOH \rightarrow Na_2CO_3 + H_2O\) | Neutral oxide: has no effect on litmus and does not react with alkalis |
| Reducing action | Not a reducing agent; it is a stable, fully oxidised product and cannot reduce heated metal oxides | Strong reducing agent: reduces heated metal oxides to the metal, e.g. \(CuO + CO \rightarrow Cu + CO_2\) |
| Combustibility | Does not burn and does not support combustion (used to put out fires) | Combustible: burns in air with a blue flame, \(2CO + O_2 \rightarrow 2CO_2\) |
A further valid distinction: \(CO_2\) turns lime water milky (forming \(CaCO_3\)), whereas \(CO\) does not; and \(CO\) is highly poisonous because it combines with haemoglobin, while \(CO_2\) is not poisonous in that way.
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