Chemical that reacts with acetic acid freezes immediately I

Chemical that reacts with acetic acid, freezes immediately? I have 5mL of acetic acid and 0.1g of unknown is added. It freezes immediately. The unknown is a white powder and it smells strong.

Solution

The white unknown powder is sodium nitrite (NaNO₂).

NaNO₂ + HC₂H₃O₂ --> HNO₂ + NaC₂H₃O₂