Question

A solution was made by adding water to 0.250 g of H2Z until the volume totaled 25.00 mL. Subsequent titration required 40.50 mL of 0.100 M sodium hydroxide. Calculate the molar mass of H2Z (in g/mol).

given: H2Z(aq) + 2 NaOH(aq) → Na 2Z(aq) + 2 H2O(ℓ)

Answer 1

Number of moles of NaOH , n = Molarity x volume in L

                                            = 0.100 M x (40.50 /1000) L

                                            = 4.05x10^-3 mol

H2Z(aq) + 2 NaOH(aq) → Na 2Z(aq) + 2 H2O(ℓ)

From the balanced equation ,

2 moles of NaOH reacts with 1 mole of H₂Z

4.05x10^-3 mol of NaOH reacts with (4.05x10^-3 )/2 = 2.025 x10^-3 mole of H₂Z

Given mass of H₂Z is 0.250 g

We know that Number of moles , n = mass / molar mass

               Molar mass = mass / number of moles

                                   = 0.250 g / (2.025 x10^-3 mol)

                                                   = 123.46 g/mol

Therefore the molarmass of H₂Z is 123.46 g/mol