Titrations

[Guest]

Calculate the molar mass of a monoprotic acid anhydride if 1.25g of the acid dissolved in 50.00mL of solution needs 38.25 mL of 0.170 M sodium hydroxide for complete neutralization.

answer: 192 g/mol

Edited November 17, 2015 by frank!e

[Guest]

Okay, so I got as far as

 

n(sodium hydroxide) = cv

                                  = 0.170 x 0.03825

                                  = 0.0065025 mol

 

 

but then I realised that I don't know the moles of the monoprotic acid anhydride or the relative atomic mass. Is this a past question? Or something for a practical? Is there any equation per chance?

 

I tried using some algebra but...

 

n=cv

n=m/M

 

m/M = c/v

1.25/M = c/0.05

[kw0573]

Neutralization means the same moles of base is reacted with same moles of H₃O⁺. Because this is a monoprotic acid, the moles of hydronium consumed is equal to the moles of the acid before the titration. If, for some reason, the acid is diprotic, then the mole of the original acid is only half of the moles of hydroniums or hydroxides reacted.

0.03825L * 0.170M = 0.0065025 moles of base consumed = moles of hydronium consumed = moles of monoprotic acid before titration

molar mass is mass / moles

1.25g / 0.0065025 mol = 192.2 g/mol, as required.

[Guest]

Neutralization means the same moles of base is reacted with same moles of H₃O⁺. Because this is a monoprotic acid, the moles of hydronium consumed is equal to the moles of the acid before the titration. If, for some reason, the acid is diprotic, then the mole of the original acid is only half of the moles of hydroniums or hydroxides reacted.

0.03825L * 0.170M = 0.0065025 moles of base consumed = moles of hydronium consumed = moles of monoprotic acid before titration

molar mass is mass / moles

1.25g / 0.0065025 mol = 192.2 g/mol, as required.

 

Ah, good point ^^ Thank you for the reminder!