Ascientist measures the mass of two liquids before and after combining them. the mass after combining the liquids is less then the sum of the masses before. where is the missing mass? what type of change occured.

A chemical change occurred and a gas was produced.  

Step-by-step explanation:

If there is no chemical reaction, the Law of Conservation of Mass says that  

Total mass = Mass 1 + Mass 2

However, if the two liquids react and give off a gas, then

Total mass = Mass 1 + Mass 2 + Mass of gas

You are not measuring the mass of the gas, so the mass of the liquids after mixing is less than it was before mixing.

For example, if Liquid 1 was a solution of HCl and Liquid 2 was a solution of Na₂CO₃, they would give off CO₂ on mixing. but you would not be measuring the mass of the CO₂.

it should have an internal chamber and two thermometers sticking out of the top. the internal chamber will also be closed off from the outside.