Because you are never adding more than the substances created, nor are you creating any, but should a chemical reaction take place you could see the liquid change form into a gaseous state and that would result a loss of the liquid volume.
So to wrap it all up you can’t have more liquids than what is already there but you could always lose some due to a chemical change, hence the reason it says an open flask, the chemical change would not be collected, mass would be lost
A bowl of Fruit Loops cereal is a heterogeneous mixture because it has cereal bits of many colors floating around in milk.A bottle of balsamic vinaigrette salad dressing is a mixture that is heterogeneous, and has to be shaken up to make the mixture appear and taste more combined.Sand shaken up in a bottle of water is a heterogeneous mixture of sand particles floating around which will eventually settle to the bottom of the bottle, making it look a lot less like a mixture.<span>
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Copper wire is not an example of a pure element because although it's made by pure elements, it's not one itself. It's made by factories.
Have a nice day! :)
