About your "vodka" example: ok it's possible you would not end up with 1 kg of vodka after mixing up with water because vodka might be less dense than water. For those here unfamiliar with the metric system (and you shouldn't be), 1 liter of water weights exactly 1 kg, but that goes for WATER, not vodka.

Now, how is it possible for you to mix 500ml of vodka with 500ml of water and end up with 950ml? There's a chemical reaction that liberates steam? The MASS could be either more than 1kg, or less than 1kg, because vodka's less or more dense then water (I don't know) but the VOLUME cannot change like that...