Question

If 0.119 g of an unknown diprotic acid is being titrated with 16.0 ml of a standardized concentration of the NaOH solution (0.107 M), what is the molar mass of the unknown acid?

1) 139 g/mol
2) 70 g/mol
3) 25 g/mol
4) other

Answer 1

To find the molar mass of the unknown diprotic acid, we need to first determine the number of moles of NaOH that reacted with the acid. Using the balanced chemical equation for the reaction between the acid and NaOH, we can calculate the number of moles of NaOH and then the number of moles of the acid. Finally, by dividing the mass of the acid by the number of moles, we find that the molar mass of the unknown acid is 139 g/mol.

Step-by-step explanation:

To find the molar mass of the unknown diprotic acid, we need to first determine the number of moles of NaOH that reacted with the acid. This can be done using the balanced chemical equation for the reaction between the acid and NaOH.

For a diprotic acid, two moles of NaOH are needed to neutralize one mole of the acid. Therefore, the number of moles of NaOH can be calculated as:

# mol NaOH = (0.107 M)(0.016 L) = 0.001712 mol NaOH

Since two moles of NaOH react with one mole of the acid, the number of moles of the acid can be calculated as:

# mol acid = 0.001712 mol NaOH ÷ 2 = 0.000856 mol acid

To find the molar mass of the acid, we divide the mass of the acid by the number of moles:

Molar mass = 0.119 g ÷ 0.000856 mol = 139 g/mol

Therefore, the molar mass of the unknown acid is 139 g/mol.