Question

The tap water found in many areas of the United States leaves white deposits when it evaporates. Is this tap water a mixture or a compound' Explain.

Short answer

Tap water is a mixture, as it contains various dissolved minerals and impurities.

Step-by-step solution

Identify the Characteristics

First, recognize that tap water can leave white deposits when it evaporates. This observation gives us a clue about the nature of tap water. Mixtures typically can leave residue because they contain multiple substances.

Understand the Definitions

Recall the definitions: A mixture is composed of two or more substances physically combined, while a compound is a substance formed from two or more elements chemically bonded in fixed proportions.

Analyze Tap Water Composition

Identify that tap water usually consists of water (H₂O) along with various dissolved minerals and impurities like calcium carbonate (CaCO₃), which can leave white deposits when the water evaporates. This indicates the presence of multiple substances, not a single compound.

Conclusion

Based on the analysis, since tap water is composed of water and various dissolved solids that can leave behind residues when the water evaporates, it fits the definition of a mixture.

Key concepts

Mixture vs Compound

Understanding the difference between a mixture and a compound is essential.
A mixture consists of two or more substances that are physically combined. These substances can be separated by physical methods. Think of a salad; you can pick out each ingredient.

Compounds, on the other hand, are substances formed when two or more elements are chemically bonded in fixed proportions. Water, chemically written as H₂O, is a compound because hydrogen and oxygen are bonded together in fixed proportions.

In a mixture, the composition can vary. For instance, the amount of sugar in a glass of sweet tea can change, making it a mixture. In contrast, the ratio of hydrogen to oxygen in a water molecule is always 2:1, illustrating a fixed proportion in a compound.

In the context of tap water, the presence of other substances like dissolved minerals, indicates that it is a mixture.

Residue Formation

When tap water evaporates, it often leaves behind a white residue. This residue can be composed of minerals such as calcium carbonate (CaCO₃) that are dissolved in the water.
As the water evaporates, these minerals do not evaporate with it. They are left behind, forming a visible deposit.

This is an important clue in determining whether tap water is a mixture or a compound. If tap water were a compound, it would consist of molecules that break up completely when evaporating, leaving no residue. So, the formation of residue indicates that tap water contains different substances mixed together physically, not chemically bound in fixed proportions.

• Residue formation signifies the presence of multiple substances.
• Tap water contains dissolved minerals and impurities.
• These substances can be separated by physical processes.

Tap Water Composition

Tap water is made up of more than just H₂O. It includes dissolved minerals and impurities such as calcium carbonate (CaCO₃), magnesium, chlorides, and other trace elements.
These additions come from natural sources, treatment processes, and pipes that transport the water.

This diverse composition is why tap water is considered a mixture. The substances are physically combined and can vary based on location and the water source.

• Common minerals in tap water include calcium, magnesium, and chloride.
• The composition of tap water can vary.
• Sources include natural water bodies, treatment processes, and transportation pipelines.

Therefore, the varying substances and the potential for residue formation clearly show that tap water is a mixture, not a compound.