Question

A student weighed out a sample of acid powder and found the mass to be 1.42 g. When the solution turned pink, the student read the burette accurately and found it to be 32.48 mL. If the base concentration is 0.1426 M, what is the molecular weight of the unknown acid

Answer 1

306.6g/mol

Step-by-step explanation:

To calculate molecular weight you need to know how many grams ou have in a determined amount of moles of substance. As you have the mass of the sample (1.42g), you need to find how many moles are, as follows:

The reaction of the acid HX with the base YOH is:

HX + YOH → H₂O + YX

1 mole of acid reacts per mole of base.

In a titration, the solution turned pink when moles base = moles acid.

Moles of base that the student added (Using the volume and molarity of the solution) are:

32.48mL = 0.03248L ₓ (0.1426 moles base / L) = 0.004632 moles of base

As the titration is in equivalence point, there are 0.004632 moles of the acid

Molecular weight (Ratio between grams of sample and its moles) is:

1.42g / 0.004632 moles =

306.6g/mol