Mole Concept

A hydrated salt is a salt which incorporates water into its crystal structure, and this associated water is called water of crystallization. The water of crystallisation affects the geometric shape and colour of the crystals.   In this experiment, the number of moles of water of crystallisation of ammonium ferrous sulphate was determined using the application of mole concept. A mole is defined as the amount of substance which contains as many elementary particles as there are atoms in 0.012 kg of carbon-12 equal to Avogrado’s number of molecules (6.022 x 1023/ mol).
The actual mass of water present in the sample was determined by heating the sample in a glass tube until a constant weight was attained. It was assumed that all of the water was driven off during heating once a constant mass was attained. In effect, the water of crystallisation was removed during this heating, and this water loss is called efflorescence. Before efflorescence, the crystals were purple in colour, while the anhydrous salt was brown in colour.
The calculations are shown above, and based on the calculations, it was calculated that a total of 0.344 moles of water was removed during heating, and it was further calculated that 11.86 moles of water was bound to the salt. Hence, the formula for the hydrated salt is ...........................
Possible errors in this experiment could have arisen during cooling of the salt before weighing due to deliquescent properties of the salt under study, which would result in the salt reabsorbing water from the atmosphere. This could have been minimised by using a dessicator during cooling. If this was occurring then that means that the formula deduced above is incorrect and the water of crystallisation should be more than determined here.