Fix the mistake: Aqueous solution

Properties of Aqueous Solutions and Dissolution

Sugar seems to disappear when placed in water, but it has not really vanished. We will learn how aqueous solutions work.

Basic Knowledge

A liquid such as water that dissolves a substance is called the solvent, the substance that dissolves is the solute, and the entire liquid formed is called the solution. A solution whose solvent is water is specifically called an aqueous solution.
Aqueous solutions have three common properties.
① They are transparent (they may be colored as long as they are transparent; for example, copper sulfate solution is blue but transparent).
② Their concentration is the same everywhere (the solute does not settle at the bottom over time).
③ The solute particles are extremely small and pass through filter paper (they cannot be separated by filtration).
The solute is completely separated into molecules and ions and spreads uniformly throughout the solvent.

Important Terms
Solute（the substance that dissolves. Table salt, sugar, and so on）
Solvent（the liquid that dissolves a substance. Water is a typical example）
Solution（solvent + solute. If the solvent is water, it is an aqueous solution）
Dissolution（the phenomenon in which a substance disperses uniformly in a solvent）
Saturated aqueous solution（an aqueous solution in which no more solute can dissolve）
Solubility（the maximum amount of solute [g] that dissolves in 100g of water）

Further Exploration (Background and Significance)

The essence of dissolution is that solute particles enter between solvent particles and diffuse uniformly. Even when sugar dissolves in water, mass does not change, so the law of conservation of mass holds (10g of sugar + 90g of water = 100g of sugar water). This is because the substance has not disappeared; it has only dispersed.
Some combinations dissolve more easily than others. Polar substances such as table salt and sugar dissolve well in water (a polar solvent), while nonpolar substances such as oil-based ink dissolve well in oil (a nonpolar solvent). “Like dissolves like” is an important principle in chemistry.

Key Points
  • Solution = solute + solvent
  • Three conditions of an aqueous solution = transparent, uniform, and very small particles
  • Mass is conserved when a substance dissolves (sugar + water = sugar water)
  • Colored aqueous solutions exist (they are acceptable if transparent)
  • Saturated = no more solute can dissolve
  • Solubility = the maximum amount that dissolves in 100g of water
  • Like dissolves like

Points to Note (Easily Confused)

① Transparent and colorless are different. A solution can be colored and still be transparent if objects can be seen through it. ② A solute can be a solid, liquid, or gas (CO2 in carbonated water and ethanol in alcoholic drinks). ③ Dissolving and melting are different phenomena. ④ Milk is opaque and settles at the bottom, so it is not an aqueous solution (it is a colloid).

Practice

  1. State the three characteristics of an aqueous solution.
  2. If 20g of sugar is completely dissolved in 80g of water, what is the mass of the entire aqueous solution?
  3. Explain why milk cannot be called an aqueous solution.

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