Final answer:
To calculate the number of molecules of water of crystallization in BaCl2.XH2O, use the stoichiometry of its reaction with AgNO3 to precipitate chloride ions. The moles of AgNO3 indicate the moles of BaCl2 reacting, from which the number of water molecules associated with BaCl2 can be inferred.
Step-by-step explanation:
The student is asking how to calculate the number of molecules of water of crystallization in a sample of hydrated barium chloride (BaCl2.XH2O) given its reaction with silver nitrate (AgNO3). The information provided indicates the reaction with silver nitrate is used for the complete precipitation of the chloride ions present in the barium chloride sample.
First, we determine the molarity of barium chloride in the solution prepared by the student. Using the reaction stoichiometry and the fact that silver chloride precipitates in a 1:1 ratio with the chloride ions in the barium chloride solution, the amount of barium chloride that reacted can be calculated. Knowing the amount of BaCl2 initially dissolved in water and comparing it with the amount that reacted with silver nitrate, we can deduce the amount of water of crystallization associated with each molecule of BaCl2.
To solve this, we begin by finding the moles of AgNO3, which is equal to the volume of AgNO3 solution times its normality. Then we calculate the moles of BaCl2 that reacted. This will be equal to the moles of AgNO3 used due to the 1:1 molar ratio of chloride to silver ion, leading to the formation of AgCl. Knowing the molar mass of BaCl2 and the number of moles present, we can find the mass of anhydrous BaCl2 that would react. Subtracting this mass from the total mass of hydrated BaCl2 used, we can estimate the mass of water present and then find X, the number of water molecules per formula unit of BaCl2 within the hydrated compound.