Question

What is the precipitate that will form from the reaction of barium chloride dihydrate with sodium sulfate decahydrate?

Answer 1

 immediate milky appearance 
after 5-10 minutes a precipitate of BaSO4 will settle out of solution the the solution will be clear.
but mostly a white precipitate

Answer 2

The formation of an insoluble salt on mixing of two solutions which contains soluble salts is refer to a precipitation reaction. The insoluble salt formed in the reaction is said to be a precipitate and can be separated by filtration or any other separation method.

The formula for barium chloride dihydrate is $BaCl_2.2H_2O$.

The formula for sodium sulfate decahydrate is $Na_2SO_4.10H_2O$.

The hydrates on the above compounds represents that they are in the aqueous phase. So, the reaction is:

$BaCl_2(aq) + Na_2SO_4(aq) \rightarrow BaSO_4(s) + NaCl(aq)$

The above equation is not balanced as the number of atoms of elements on the reactant side is not equal to the number of atoms of elements on the product side. So, in order to balance the reaction, $NaCl$ on the reactant side is multiplied by 2. Thus, the balanced chemical equation is:

$BaCl_2(aq) + Na_2SO_4(aq) \rightarrow BaSO_4(s) + 2NaCl(aq)$

Hence, the precipitate that will form from the reaction of barium chloride dihydrate with sodium sulfate decahydrate is barium sulfate, $BaSO_4$.