A 0.120 g sample of a diprotic acid of unknown molar mass is dissolved in water and titrated with 0.1218 M NaOH. The equivalence point is reached after adding 12.4 mL of base.
What is the molar mass of the unknown substance?
To find the molar mass of the unknown substance, we need to use the concept of stoichiometry and the information provided.
First, let's determine the number of moles of NaOH used in the titration. We can do this by multiplying the volume of NaOH used (12.4 mL) by its molarity (0.1218 mol/L):
Number of moles of NaOH = volume × molarity
= 0.0124 L × 0.1218 mol/L
= 0.00150832 mol
Since the reaction between the acidic sample and NaOH is a 1:2 ratio, we can conclude that the number of moles of the unknown substance (diprotic acid) is twice the number of moles of NaOH used:
Number of moles of diprotic acid = 2 × Number of moles of NaOH
= 2 × 0.00150832 mol
= 0.00301664 mol
Now, using the mass of the diprotic acid sample (0.120 g) and the number of moles calculated, we can find the molar mass of the unknown substance by dividing the mass by the number of moles:
Molar mass = Mass of diprotic acid / Number of moles of diprotic acid
= 0.120 g / 0.00301664 mol
Calculating this division, we find:
Molar mass = 39.775 g/mol
Therefore, the molar mass of the unknown diprotic acid substance is approximately 39.775 g/mol.