High School

0.104 g of an unknown diprotic acid was weighed into a flask and dissolved in 150 mL of water. The resulting solution was titrated using 46.5 mL of 0.103 M NaOH. Calculate the molar mass of the unknown diprotic acid.

Answer :

The molar mass of the unknown diprotic acid, given that 0.104 g of the acid was dissolved in 150 mL of water is 43.42 g/mol

How do I determine the molar mass?

First, we shall dtermine the mole of NaOH. This can be obtained as follow:

  • Volume = 46.5 mL = 46.5 / 1000 = 0.0465 L
  • Molarity of NaOH = 0.103 M
  • Mole of NaOH =?

Mole = Molarity x Volume

Mole of NaOH = 0.103 × 0.0465

Mole of NaOH = 0.00479 mole

Finally, we shall determine the molar mass of the unknown diprotic acid. Details below:

Balanced equation:

H₂X + 2NaOH —> Na₂X + 2H₂O

Note: H₂X is the diprotic acid

From the balanced equation above,

2 moles of NaOH reacted with 1 mole of H₂X.

Therefore,

0.00479 mole of NaOH will react with = 0.00479 / 2 = 0.002395 mole of H₂X.

  • Mole of diprotic acid = 0.002395 mole
  • Mass of diprotic acid = 0.104 g
  • Molar mass of diprotic acid =?

Molar mass = mass / mole

Molar mass of diprotic acid = 0.104 / 0.002395

Molar mass of diprotic acid = 43.42 g/mol

Thus, the molar mass of the diprotic acid is 43.42 g/mol

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Final answer:

To calculate the molar mass of the unknown diprotic acid, use the concept of stoichiometry and determine the number of moles of NaOH used in the titration. Then, use the balanced chemical equation to determine the mole ratio between the unknown diprotic acid and NaOH. Finally, calculate the molar mass of the unknown diprotic acid by dividing the mass of the unknown diprotic acid by the moles of the unknown diprotic acid.

Explanation:

To calculate the molar mass of the unknown diprotic acid, we need to use the concept of stoichiometry. First, we need to determine the number of moles of the NaOH used in the titration:

Moles of NaOH = Molarity of NaOH x Volume of NaOH used

Next, we need to use the balanced chemical equation for the reaction between the unknown diprotic acid and NaOH to determine the mole ratio between the two:

Moles of unknown diprotic acid = Moles of NaOH x (1 mole of unknown diprotic acid / 2 moles of NaOH)

Finally, we can calculate the molar mass of the unknown diprotic acid:

Molar mass = Mass of unknown diprotic acid / Moles of unknown diprotic acid