Chem-help me

2008-05-06 5:03 am

1. Orange juice contains citric acid. The relative molecular mass of citric acid is 192. In a sample of orange juice, the concentration of citric acid is 8.06g dm-3 . 25.0 cm3 of the sample require 7.50 cm3 of 0.420M sodium hydroxide solution for complete neutralization. Determine the basicity of citric acid.

Please write down the chemical equation, thank you.

回答 (1)

Uncle Michael

2008-05-06 7:11 am

✔ 最佳答案

Let n be the basicity of citric acid.
Thus, denote citric acid as HnA.

Consider 1 dm3 of HnA solution:
Mass of HnA = 8.06 g
No. of moles of HnA = mass/(molar mass) = 8.06/192 = 0.0420 mol
Molarity of HnA = mol/V = 0.0420/1 = 0.0420 M

Consider the neutralization between HnA and NaOH.
HnA + nNaOH → NanA + nH2O
No. of moles of HnA used = MV = 0.0420 x (25/1000) = 0.00105 mol
No. of moles of NaOH used = MV = 0.420 x (7.5/1000) = 0.00315 mol
Mole ratio HnA : NaOH = 0.00105 : 0.00315 = 1 : n
Hence, basicity of citric acid HnA, n = 3 (tribasic)

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