Oxalic acid + sodium hydroxide

2008-06-07 7:53 pm

Oxalic acid is a weak acid.Hydrated oxalic acid has the formula H2C2O4‧2H2O.
5.04 g of oxalic acid dihydrate crystals were dissolved in distilled water and made up 250.0cm^3 of solution.
25.0cm^3 of this solution required 26.6cm^3 of 0.3M of sodium hydroxide for complete neutralization.

1.What is the molarity of oxalic acid?
2.What is the basicity of oxalic acid?

回答 (1)

Uncle Michael

2008-06-08 12:17 am

✔ 最佳答案

1.
Molar mass of H2C2O4•2H2O = 1x2 + 12x2 + 16x4 + 2(1x2 + 16) = 126 g mol-1

Consider the preparation of the 250 cm3 solution.
Mass of H2C2O4•2H2O used = 5.04 g
Volume of the solution = 250 cm3 = 0.25 dm3

No. of moles of H2C2O4•2H2O used = mass/(molar mass) = 5.04/126 = 0.04 mol
No. of moles of H2C2O4 in the solution = 0.04 mol
Molarity of H2C2O4 = mol/V = 0.04/0.25 = 0.16 M

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2.

Let n be the basicity of H2C2O4, and denote the acid as HnA.

Consider the titration:
HnA + nNaOH → NanA + nH2O
Mole ratio HnA : NaOH = 1 : n

No. of moles of HnA used = MV = 0.16 x (25/1000) = 0.004 mol
No. of moles of NaOH used = MV = 0.3 x (26.6/1000) = 0.00798 mol
Mole ratio HnA : NaOH = 0.004 : 0.00798 ≈ 1 : 2
Hence, basicity of oxalic acid, n = 2
.

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