cal The data in the following plot given below were obtained for the tiration of
ID: 878407 • Letter: C
Question
cal The data in the following plot given below were obtained for the tiration of a 0.300g sample of a solid monoprotic acid with a 0.150 M KOH solution. [This is a 5 part question; each question is worth 2pts (a) What is the volume of KOH solution required to reach the stoichiometric point? (b) What is the pH at the stoichiometric point? (c) What is the pKa of the weak acid? (d) Calculate the number of moles of weak acid analyzed. (e) What is the molar mass of the solid weak acid, expressed to the correct number of significant figures? pH vs volume of a weak acid and KOH 15 14 13 12 10 6 0 2 468 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 Volume of KOH (mL)Explanation / Answer
(a) At stoichiometric point, the mol of KOH added equals to the moles of monoprotic acid present in solution.
Thus, the volume of KOH required to reach stoichiometric point from graph is 21 ml
(b) The pH at stoichiometric point.
pH = pKa
From graph pH at stoichiometric point approximately around 9.0
(c) pKa of weak acid = pH = approximately around 9.0
(d) number of moles of weak acid.
At stoichiometric point moles of weak acid in solution = moles of base added
thus, moles of acid analyzed = 0.150 M
(e) moles of acid = grams of acid / molar mass of acid
or,
molar mass of acid = grams of acid / moles of acid
moles of acid = M x L = 0.15 x 0.021 = 3.15 x 10^-3 moles
thus,
molar mass of monoprotic acid = 0.3 g / 3.15 x 10^-3 mol
= 95.24 g/mol
=
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