Select the statement that BEST answers the following question based on the information provided. Milk is uniformly mixed it contains several compounds– water, proteins, fats, and sugars. Is milk considered a substance or a mixture?
A. It is a liquid substance with uniform composition.
B. It is a mixture, only solids are pure substances,
C. It is a mixture that can be separated by physical means
D. It contains compounds and is therefore a substance
The Correct Answer and Explanation is:
The correct answer is C. It is a mixture that can be separated by physical means.
Explanation:
Milk is not a pure substance; it is a mixture because it consists of more than one type of compound or element. A substance refers to matter that has a uniform and definite composition, where all of its particles are identical and it cannot be separated into different components by physical means. Examples of substances include pure elements (like oxygen) or compounds (like water).
Milk contains several components—water, proteins, fats, and sugars—that are physically mixed together, making it a heterogeneous mixture. However, milk is often described as a homogeneous mixture because, when it is freshly mixed, it appears uniform to the naked eye. Despite this uniformity, the various compounds in milk can be separated by physical processes, such as centrifugation (to separate the fats), filtration, or evaporation. This ability to separate the components physically is characteristic of mixtures.
Let’s review the other options:
- A. It is a liquid substance with uniform composition.
This is incorrect because, while milk may appear homogeneous, it is still a mixture, not a substance. A substance must have a uniform composition that cannot be physically separated into different components. - B. It is a mixture, only solids are pure substances.
This is incorrect because pure substances are not restricted to solids. Both solid and liquid substances can be pure, but milk itself is a mixture, not a pure substance. - D. It contains compounds and is therefore a substance.
This is incorrect because the presence of compounds does not automatically make something a pure substance. Milk contains multiple compounds, but these compounds are in a mixture, not a single substance.
Thus, the best answer is C, as milk is a mixture that can be separated into its individual components through physical means.