Why is tap water a homogenous mixture, whereas distilled water is a pure substance?
The correct answer and explanation is:
Correct Answer:
Tap water is a homogeneous mixture, whereas distilled water is a pure substance, because tap water contains dissolved substances and minerals that are uniformly distributed, while distilled water contains only water molecules without any dissolved impurities.
Explanation:
The distinction between a homogeneous mixture and a pure substance lies in the uniformity and composition of the matter.
Tap water is considered a homogeneous mixture because it contains a variety of dissolved substances such as calcium, magnesium, chlorine, fluoride, and sometimes trace metals. These components are not visible to the naked eye and are evenly distributed throughout the solution, making the composition uniform. Since the different substances are mixed at the molecular level and cannot be separated by simple physical means like filtration, tap water qualifies as a homogeneous mixture. Despite looking clear and clean, the presence of these dissolved solutes means it is not a pure substance.
Distilled water, on the other hand, is water that has been purified through the process of distillation. This process involves boiling the water to produce steam and then condensing the steam back into liquid form. The boiling and condensation remove most dissolved substances and impurities, including salts, minerals, and organic materials. What remains is nearly 100 percent H₂O molecules, making distilled water a pure substance. It has a consistent and definite composition throughout and does not contain any other types of atoms or molecules mixed in.
In summary, tap water contains additional components that make it a mixture, even though it looks uniform, while distilled water has only one type of particle, H₂O, making it a pure substance by definition.