Question

An unknown diprotic acid was fully titrated with 0.1599 M sodium hydroxide solution to determine the molar mass of the unknown. If it took 34.98 mL of sodium hydroxide solution to fully react with 0.2518 g of unknown acid, determine the molar mass of the acid (in g/mol). Molar mass of diprotic acid: g/mol

Answer 1

we have the Balanced chemical equation as:

2 NaOH + H2A ---> Na2A + 2 H2O

lets calculate the mol of NaOH

volume , V = 34.98 mL

= 3.498*10^-2 L

we have below equation to be used:

number of mol,

n = Molarity * Volume

= 0.1599*0.035

= 5.593*10^-3 mol

From balanced chemical reaction, we see that

when 2 mol of NaOH reacts, 1 mol of H2A reacts

mol of H2A reacted = (1/2)* moles of NaOH

= (1/2)*5.593*10^-3

= 2.797*10^-3 mol

This is number of moles of H2A

mass of H2A = 0.2518 g

we have below equation to be used:

number of mol = mass / molar mass

2.797*10^-3 mol = (0.2518 g)/molar mass

molar mass = 90.04 g/mol

Answer: 90.0 g/mol