Final answer:
Potassium ferricyanide cannot be substituted for potassium ferrocyanide in a calcium ion identification test. The ferrocyanide ion [Fe(CN)6]4- is very stable in solution, leading to a negligible concentration of free cyanide ions. Moles and grams are related by molar mass, which is essential when preparing solutions of specific concentrations.
Step-by-step explanation:
To perform the identification test of calcium ion in calcium gluconate, typically, potassium ferrocyanide is used. However, if potassium ferrocyanide is unavailable, one cannot simply substitute it with potassium ferricyanide because they are different chemicals that react in different ways. For correctly identifying calcium ions, it is essential to use the appropriate reagent as specified in the test protocol or to find a suitable alternative that serves the same purpose.
Regarding the stability of ferrocyanide ion, indeed, the ferrocyanide ion, [Fe(CN)6]4-, has a very high formation constant, Kf, which indicates that it does not dissociate easily into its constituent ions in solution. Therefore, the concentration of cyanide ion, CN-, in equilibrium with a 0.65 M solution of K4[Fe(CN)6] would be extremely low, as most of the cyanide would be bound within the stable ferrocyanide complex.
Lastly, when preparing a solution of an ionic compound such as potassium dichromate, knowing the molar mass is crucial because moles and grams are related through this property. To calculate the required number of grams to achieve a specific molarity, one must multiply the number of moles by the molar mass of the compound.