Question

A chemist weighs out 0.138 grams of a unknown diprotic acid into a 222 volumetric flask and makes a 222 ml solution of it with distilled water. They titrate this solution with 0.1800 M Magnesium hydroxide. When the titration reached the equivalence point, the chemist found that they had added 22.8 mL of magnesium hydroxide. Calculate the molar mass of the unknown acid.

Answer 1

33.6g/mol is the molar mass of the unknown acid

Step-by-step explanation:

The molar mass of a substance is defined as the ratio of the mass of the acid (0.138g) and the moles of the substance.

The diprotic acid, H₂X, reacts with magnesium hydroxide, Mg(OH)₂ as follows:

H₂X + Mg(OH)₂ → MgX + 2H₂O

Where 1 mole of the diprotic acid reacts per mole of magnesium hydroxide

To find the moles of the acid and solve the molar mass of it we need to find the moles of magnesium hydroxide added to the solution at equivalence point = Moles of diprotic acid as follows:

22.8mL = 0.0228L * (0.1800moles / L) = 4.104x10⁻³ moles of the acid.

The molar mass is:

0.138g / 4.104x10⁻³ moles =

33.6g/mol is the molar mass of the unknown acid