Which of the following mixtures could NOT be separated into its components through decanting?
A. Beans in hot water
B. Noodles in water
C. Pebbles in water
D. Salt and water
The correct answer and explanation is:
Correct Answer: D. Salt and water
Decantation is a physical method used to separate mixtures by removing a liquid layer that is free of precipitate or sediment. It works best when the components of the mixture differ significantly in phase or density, such as a solid in a liquid. The technique involves carefully pouring off the liquid, leaving behind the solid or denser material that has settled at the bottom.
In the case of salt and water, the two substances form a homogeneous mixture or solution. Salt dissolves completely in water, meaning the salt particles are evenly distributed and no longer exist as separate solid particles. There is no visible boundary or layer that can be poured off. Therefore, decantation cannot be used to separate salt from water. Instead, separation would require techniques like evaporation or distillation, which can separate dissolved substances based on boiling point differences or changes in state.
On the other hand, beans in hot water, noodles in water, and pebbles in water all form heterogeneous mixtures. In these cases, the solids do not dissolve but remain separate from the liquid. After allowing the solids to settle or float, one can easily pour off the water while leaving the solids behind, which is the principle of decantation. These examples involve clearly distinguishable phases, which makes decantation an effective separation method.
In summary, decantation is only useful for separating substances that do not mix at the molecular level. Since salt dissolves fully in water to form a solution, it cannot be separated through decanting, making salt and water the correct answer to this question.