What happened when a drop of the sodium carbonate solution was mixed with the magnesium sulfate?

The formation of magnesium carbonate in the form of a precipitate and sodium sulfate as a byproduct takes place.

Explanation:

When a drop of sodium carbonate is mixed with the magnesium sulfate, the formation of MgCO3, magnesium carbonate as a precipitate, and Na2SO4, sodium sulfate as a byproduct takes place. One can separate magnesium carbonate from the sodium sulfate by using the process of filtration. The chemical reaction that takes place in the process is:  

MgSO4 (aq) + Na2SO4 (aq) ⇒ MgCO3 (s) + Na2SO4 (aq)

A separation process in which the formation of solid takes place in a solution after undergoing a chemical reaction is termed as precipitation. The precipitate is the name given to the solid substance that gets produced in the reaction. The precipitate formed can be withdrawn from the solution with the help of a physical separation procedure like filtration.  

it would be a gas formation

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