Question 22

Sodium chloride crystals are a pure substance.

A pure substance consists of a single type of particle, and sodium chloride crystals fit this definition as they are composed entirely of sodium and chloride ions.

A) Granite rock

Granite rock is not a pure substance as it is composed of multiple minerals, including quartz, feldspar, and mica. These various components make granite a mixture rather than a single substance.

B) Toothpaste

Toothpaste is a mixture of various compounds, including abrasives, fluoride, flavoring agents, and thickening agents. This combination of different ingredients means that toothpaste cannot be classified as a pure substance.

C) Sodium chloride crystals

Sodium chloride crystals are classified as a pure substance because they consist solely of sodium ions and chloride ions in a fixed ratio. This uniform composition is what defines them as a pure substance.

D) Sugar water

Sugar water is a solution, where sugar is dissolved in water, creating a mixture rather than a pure substance. The presence of two different components (sugar and water) disqualifies it from being a pure substance.

Conclusion

Sodium chloride crystals are definitively identified as a pure substance due to their uniform composition of sodium and chloride ions. In contrast, granite rock, toothpaste, and sugar water contain multiple components, making them mixtures and therefore not pure substances.