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 acid?
To find the molar mass of the unknown acid, we need to use the balanced chemical equation of the reaction between the diprotic acid and sodium hydroxide, and the volume and concentration of sodium hydroxide used in the titration.
The balanced equation for the reaction between a diprotic acid (HA) and sodium hydroxide (NaOH) is:
HA + 2NaOH -> Na2A + 2H2O
From the equation, we can see that one mole of HA reacts with two moles of NaOH.
Given:
- Mass of the unknown acid = 0.120 g
- Volume of NaOH used (in mL) = 12.4 mL
- Concentration of NaOH = 0.1218 M
First, we need to convert the volume of NaOH used to liters:
12.4 mL * (1 L / 1000 mL) = 0.0124 L
Next, we can use the information from the balanced equation and the volume and concentration of NaOH to calculate the number of moles of NaOH used in the titration:
Moles of NaOH = Volume (in L) * Concentration (in M)
Moles of NaOH = 0.0124 L * 0.1218 M = 0.0015088 moles
Since the balanced equation shows that 1 mole of HA reacts with 2 moles of NaOH, we can determine the moles of HA:
Moles of HA = 0.0015088 moles / 2 = 0.0007544 moles
Finally, we can calculate the molar mass of the unknown acid using the formula:
Molar mass (g/mol) = Mass (g) / Moles
Molar mass = 0.120 g / 0.0007544 moles
Calculating this gives us the molar mass of the unknown acid.