question_answer 127)

  A sample of ferrous oxide has actual formula. In this sample, what fraction of metal ions are Fe2+ions? What type of non-stoichiometric defect is present in this sample?  

Answer:

                  Let the formula of the sample be                                                      On looking at the given formula of the compound             X + y = 0.93                                   ... (i) Total positive charge on ferrous and ferric ions should balance the two units of negative charge on oxygen Therefore,           2x + 3y =2                                   ...(ii) Þ                                                  ... (iii) On subtracting equation (i) from equation (iii) we have                          On putting the value of y in equation (i), we get                     x + 0.14 =0.93                     x = 0.93 - 0.14 Þ                     x = 0.79 Fraction of Fe2+ ions present in the sample                                   = = 0.849 Metal deficiency defect is present in the sample because iron is less in amount than that required for stoichiometric composition.