Question

I conducted an experiment in lab to synthesize copper(II) and iron(II) oxalate. I calculated a final mass of 7.4202g K_3[Fe(C_2O_4)_3] x 3H_2O (g). In order to find the theoretical mass of this substance, do I assume that theoretical mass is equal to the molar mass of that product formed? Then to find % yield - take the actual mass of 7.4202g/theoretical (491.326g)x100? I feel as though I am missing something here. Can someone please explain and help me solve this problem? Thank you.

Answer 1

% yield = (actual yield / theoritical yield) x 100

Theoretical yield is calculated based on the limiting reagent. Limiting reagent is one of your reactant.

For your reference, I am giving an example.

Theoritical yield

Cyclohexene + oxone ------------------> cyclohexane-1,2-diol

Oxone :

mass of oxone = 0.40 g

molar mass of oxone = 152.16 gmol-1

Moles of oxone = mass of oxone / molar mass of oxone

                         = 0.40 g/ 152.16 gmol-1

                        = 0.00263 mol

moles of oxone = 0.00263 mol

Cyclohexene:

volume of cyclohexene = 50 micro litres

                                    = 50 x 10^-6 L

                                   = 50x 10^-6 x 1000 cm³

                                  = 50x 10^-3 cm³

density of cyclohexene = 0.811 g/ cm³

Hence, mass of cyclohexene = volume of cyclohexene x density of cyclohexene

                                            = (50x 10^-3 cm³) (0.811 g/ cm³)

                                           = 0.04 g

molar mass of cyclohexene = 82.0 g mol-1

moles of cyclohexene = mass of cyclohexene / molar mass of cyclohexene

                                   = 0.04 g/ 82.0 g mol-1

                                   = 0.00048 mol

Hence, moles of cyclohexene = 0.00048 mol

            moles of oxone            = 0.00283 mol

Therefore, cyclohexene is present in lesser amount. Hence cyclohexene is the limiting reagent.

              Theoretical yield is calculated based on limiting reagent i.e. cyclohexene.

Theoretical yield :

     Cyclohexene ------------------> cyclohexane-1,2-diol

      1mol=   82 g                              1 mol = 116 g

           0.04 g                                            ?

          ? = (0.04 g/ 82g ) x 116 g

            = 0.056 g

      ? = 0.056 g

Therefore, theoretical yield = 0.056 g