Is a sugar cube dissolved in water a pure substance or mixture? Explain
The Correct Answer and Explanation is:
Answer:
A sugar cube dissolved in water is a mixture, specifically a homogeneous mixture (also called a solution), not a pure substance.
Explanation
A pure substance is a form of matter that has a constant composition and uniform properties throughout. Examples include elements like gold or oxygen, and compounds like pure water (H₂O) or pure sugar (sucrose, C₁₂H₂₂O₁₁). These substances cannot be separated into other kinds of matter by physical means. They have definite physical and chemical properties such as melting point, boiling point, and density.
When a sugar cube is dissolved in water, it undergoes a physical change — the sugar breaks down into individual molecules and disperses evenly throughout the water. The resulting liquid looks uniform throughout and has only one visible phase. However, this is no longer a pure substance. It is a homogeneous mixture or solution, meaning it consists of two or more substances (in this case, sugar and water) that are uniformly mixed at the molecular level.
The key reason it is a mixture and not a pure substance is that the sugar and water retain their individual chemical identities. The sugar can still be separated from the water through processes like evaporation or distillation. No new substance is formed; instead, the components simply combine physically, not chemically.
Additionally, the ratio of sugar to water can vary — you can add more or less sugar, creating solutions of different concentrations. This variability is another hallmark of mixtures, as pure substances always have a fixed composition.
In summary, although the dissolved sugar seems to “disappear,” it forms a solution with water — a uniform mixture, not a chemically pure substance. Therefore, a sugar cube dissolved in water is a homogeneous mixture, not a pure substance.
