Dissolving ：練習問題

What term is used to describe a substance that dissolves in a liquid to form a solution?

Which of the following changes would decrease the rate at which a solid substance dissolves in a liquid solvent?

A student has a saturated potassium nitrate solution at \( 60^\circ\text{C} \). She divides the solution equally into two beakers, A and B.

(1) Beaker A is cooled to \( 20^\circ\text{C} \).
(2) In Beaker B, half of the water is evaporated at \( 60^\circ\text{C} \).

Given that the solubility of potassium nitrate is \( 110\text{ g}/100\text{ g} \) water at \( 60^\circ\text{C} \) and \( 32\text{ g}/100\text{ g} \) water at \( 20^\circ\text{C} \), which process results in the crystallization of a greater mass of solid?

Which action would generally increase the rate at which a solid substance dissolves in a liquid?

A student dissolves \( 40 \text{ g} \) of sugar in \( 150 \text{ g} \) of water. Using the particle theory, which statement best explains why the mass of the resulting solution is exactly \( 190 \text{ g} \)?

Using the particle theory, explain why the total volume of a solution is often less than the sum of the volumes of the solute and solvent when they are mixed.

When salt dissolves in water, the mass of the resulting solution is equal to the sum of the mass of the salt and the water. What scientific law does this observation support?

When a solid substance like salt dissolves in water, the final volume of the solution is often less than the sum of the initial volumes of the salt and water. Explain this phenomenon using the particle theory.

A student adds a small amount of salt to a beaker of water and stirs it until it is completely dissolved.

(a) Identify the solute and the solvent in this solution. (2 points)

(b) State whether the total mass of the salt and water changes after the salt has dissolved. (1 point)

(c) According to the particle theory, explain why the total volume decreases slightly when salt dissolves in water. (1 point)

A student added a small amount of sugar into a beaker of water and stirred the mixture. After a few minutes, the sugar disappeared and a clear solution was formed.

(a) Using the particle theory, describe the process of dissolving that occurred in the beaker. (3 points)
(b) The student measured the total mass of the sugar and the water before mixing, and then measured the mass of the resulting solution. State the relationship between these two measurements. (1 point)
(c) If the student used cold water instead of warm water, would the sugar dissolve faster or slower? Explain your answer in terms of particle motion. (1 point)