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cyw1226 2013-8-22 12:44 AM

molar mass of an acid

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chungkin81 2013-8-22 08:30 AM

25.0 cm3 of an aqueous solution contains 0.108 g of a tribasic acid X which requires 27.60 cm3 of 0.12 M NaOH(aq) for complete neutralization. What is the molar mass of the acid?

Solution:
A tribasic acid has 3 H that can be ionized as Hydrogen ions

Let the chemical formula of the tribasic acid be H3X
H3X(aq) + 3NaOH(aq) --> Na3X(aq) + 3H2O(l)
No. of moles of NaOH = 0.12 x 27.60/1000 = 3.312 x 10^-3 mol
No. of moles of H3X = (3.312 x 10^-3) / 3 = 1.104 x 10^-3 mol

Let the molar mass of H3X be M
M x  1.104 x 10^-3 = 0.108
M = 97.8 g mol-1

The molar mass of the tribasic acid is 97.8 g mol-1.
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