Keri has to identify a mysterious brown liquid in science class. She pours it through a filter, but the substance looks the same. Then she heats the substance and collects the water that evaporates. The water droplets look the same as the original substance. Keri concludes that since the substance cannot be separated it must be a compound. Is Keri correct?

Answer is: No, because the substance could be an element.

Pure substance is made of only one type of atom (element) or only one type of molecule, it has definite and constant composition with distinct chemical properties.

Pure substances can be separated chemically, not physically, that is difference between pure substances and mixtures.

Elements (for example copper, iron, sulfur) and compounds (water, sodium chloride) have definite and constant composition with distinct chemical properties.

The answer is NO. It can not be a compound it is an element.

In a component mixture it can be separated physically way from the other.

In element it can be only separated by a way of destroying the compound itself by chemical reaction.