Question

A solution of the weak acid HA is prepared by dissolving 2.60 g of HA in 100.0 mL water. The solution is titrated, and the equivalence point is reached after 32.6 mL of 0.500 M NaOH is dispensed. Calculate the molar mass of HA.

Answer 1

The molar mass of the weak acid HA is 159.51 g/mol, calculated by dividing the initial mass of HA by the moles of HA, which is equivalent to the moles of the titrant NaOH at the equivalence point.

Step-by-step explanation:

To calculate the molar mass of the weak acid HA, we first need to determine the moles of NaOH that reacted at the equivalence point. From the given volume and molarity, we can find the number of moles of NaOH and therefore HA, since they react in a 1:1 molar ratio. The calculation is as follows:

# mol NaOH = Volume NaOH (L) × Molarity NaOH (M)

# mol NaOH = 0.0326 L × 0.500 M = 0.0163 mol

Since at the equivalence point the moles of NaOH and HA are equal, we have:

# mol HA = # mol NaOH = 0.0163 mol

The molar mass of HA can then be determined by dividing the mass of HA by the number of moles:

Molar mass HA = Mass HA (g) / # mol HA

Molar mass HA = 2.60 g / 0.0163 mol

Molar mass HA = 159.51 g/mol

The molar mass of HA is therefore 159.51 g/mol.