Dissolving ：練習問題

A student places a \( 1\text{ g} \) crystal of purple potassium permanganate at the bottom of a beaker of still water. After several hours, the entire beaker becomes a uniform purple colour even without stirring. This observation provides evidence that in the process of Dissolving:

Which of the following substances acts as an insoluble solute when added to pure water at room temperature?

Consider a situation where a liquid is evaporating from a solution. How would the concentration of the solute in the remaining liquid change, assuming no further solute is added and the solute itself is non-volatile?

When a solid substance mixes evenly with a liquid to form a uniform mixture, the solid substance is referred to as the:

A mixture contains sand, common salt, and water. Which sequence of practical procedures should be used to separate and obtain dry sand and dry common salt from this mixture?

In a solution, when one substance disappears into another to form a homogeneous mixture, what is the substance that does the dissolving called?

A student observes that \( 5\text{ g} \) of fine sugar powder dissolves faster than a \( 5\text{ g} \) sugar cube in the same volume of water. Explain this observation by referring to surface area and particle collisions.

A student adds a small amount of salt to a saturated solution that already has undissolved salt at the bottom. Explain why the mass of the mixture increases but the concentration of the liquid portion remains the same.

A student sets up an experiment to investigate the dissolving properties of different solids in water. They add a small spoonful of each substance to separate beakers containing \(100 \text{ cm}^3\) of room temperature water and stir each mixture for one minute.

• Beaker 1: Contains table salt, and the solid completely disappears, forming a clear liquid.
• Beaker 2: Contains sand, and the solid settles at the bottom, making the liquid cloudy.
• Beaker 3: Contains sugar, and the solid completely disappears, forming a clear liquid.

A student adds exactly \(25\text{ g}\) of salt to a beaker containing \(100\text{ g}\) of water (volume \(100\text{ cm}^3\)).
(a) After stirring, the salt completely disappears. State the total mass of the resulting solution and name the law this illustrates. (2 points)
(b) The student observes that the final volume of the solution is approximately \(108\text{ cm}^3\), which is less than the sum of the initial volumes of salt (\(\approx 11.5\text{ cm}^3\)) and water. Use the particle theory to explain this observation. (2 points)
(c) Describe two ways the student could have increased the rate of dissolving in this experiment and explain one of them using particle collisions. (2 points)