Question

Calculate the molecular weight of your unknown acid if it had four reactive protons and reacted with the same amount of NaOH as you measured in this experiment?

Answer 1

Q1. Let the acid be H₄A

The reaction equation with NaOH will be : H₄A (aq) + 4 NaOH (aq) Na₄A (aq) + 4 H₂O (l)

For trial 1,

moles NaOH reacted = 0.00191081 mol

moles unknown acid = (1/4) * (moles NaOH reacted)

moles unknown acid = (0.25) * (0.00191081 mol)

moles unknown acid = 0.0004777 mol

molar mass unknown acid = (mass unknown acid) / (moles unknown acid)

molar mass unknown acid = (0.2 g) / (0.0004777 mol)

molar mass unknown acid = 418.67 g/mol

Similarly, for trial 2, molar mass unknown acid = 404.71 g/mol

for trial 3, molar mass unknown acid = 466.98 g/mol

Average molar mass = (418.67 g/mol + 404.71 g/mol + 466.98 g/mol) / 3

Average molar mass = (1290.36 g/mol) / 3

Average molar mass = 430.12 g/mol