Copper(I) Iodide is synthesised by the equation:

2CuSO4.5H2O + 2KI + 2Na2S2O3.5H2O --> 2CuI + K2SO4 + Na2SO4 + Na2S4O6 + 10H2O

Would it make a difference if anhydrous CuSO4 and Na2S2O3 are used instead? Why hydrous CuSO4 and Na2S2O3 are used instead?

I'm sure the primary reason is that is the way CuSO4 and Na2S2O3 come. I'm also sure that if the anhydrous material is placed in water they will pick up water of hydration. I know for a fact that CuSO4 will and I'm relatively sure Na2S2O3 will do the same.

Using anhydrous CuSO4 (copper(II) sulfate) and Na2S2O3 (sodium thiosulfate) instead of hydrous CuSO4.5H2O and Na2S2O3.5H2O in the synthesis of Copper(I) Iodide would make a difference.

Hydrous compounds contain water molecules within their crystalline structure, which can act as ligands (molecules or ions attached to a central metal atom) in a chemical reaction. In this specific synthesis reaction, the water molecules present in CuSO4.5H2O and Na2S2O3.5H2O play important roles.

The hydrous CuSO4 provides copper(II) ions, which undergo reduction to copper(I) ions during the reaction. The water molecules attached to CuSO4.5H2O ligands facilitate this reduction process by donating protons (H+). Without the presence of water, anhydrous CuSO4 would not be able to provide the necessary protons for the reduction to occur effectively.

Similarly, the hydrous Na2S2O3 serves as a reducing agent in the reaction by providing sulfur in an oxidation state of +2. Water molecules associated with Na2S2O3.5H2O molecules assist in the redox reactions by stabilizing and activating reactant molecules. Anhydrous Na2S2O3 lacks the water molecules that play a crucial role in facilitating these redox reactions.

In summary, hydrous forms of CuSO4 and Na2S2O3 are used in the synthesis of Copper(I) Iodide because the water molecules associated with these compounds contribute to the necessary reactions. Removing the water from the equation by using anhydrous compounds would significantly alter the reaction mechanism and may impact the yield or efficiency of the synthesis.