Na2C2O4係acidic or alkali??

Sodium ethanedioate (Na2C2O4) form an alkaline solution when it is dissolved in water.

When sodium ethanedioate solution dissolves in water, it gives Na+(aq) ion and C2O4-(aq) ion.

Na+(aq) comes from the strong alkali NaOH, and thus Na+(aq) ion does not react with water.

C2O42-(aq) ion comes from the ionization of a weak acid HC2O4-(aq) ion, so that C2O42‑(aq) ion would be hydrolysed in water to form HC2O4-(aq) and OH-(aq).
C2O42-(aq) + H2O(l) → HC2O4-(aq) + OH-(aq)
Therefore, the concentration of OH-(aq) ion is higher than that of H+(aq), and thus the solution is alkaline.

2009-09-25 13:36:08 補充：
You will learn in AL Chemistry that phenolphthalein changes its colour in a slightly alkaline solution, but not a neutral solution. In a neutral solution, phenolphthalein is colourless.

2009-09-25 13:41:19 補充：
Above pH 10.0, phenolphthalein is red (or deep pink).
Below pH 8.3, phenolphthalein is colourless.
Between pH 8.3 -10.0, phenolphthalein is changing colour (pale pink).

其實隻 H2C2O4我冇估錯既話應該係 HOOC-COOH(乙二酸),係一隻酸黎既,咁簡單d去睇...d個反應該都之不過係中和反應,所以出黎個product(NaOOC-COONa)都應該係中性(鹽)......

must be acid.O4=acid

2009-09-20 12:28:08 補充：
Disodium oxalate is a sodium salt of oxalic acid with the molecular formula Na2C2O4. It can act as a reducing agent, and it may be used as a primary standard for standardizing potassium permanganate KMnO4 solutions.

2009-09-20 12:29:38 補充：
Disodium oxalate is frequently referred to as sodium oxalate. Since the polyatomic ion of oxalate has a negative two charge, there can be no other compound consisting solely of sodium and oxalate other than disodium oxalate. Therefore, the prefix di is often dropped.