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The Amazing World of Solutes, Solvents, and Solutions - Factors Affecting Dissolution Rate

Grade 8CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

A Solution is a homogeneous mixture of two or more substances. The substance present in smaller quantity is the Solute, and the substance in larger quantity is the Solvent.

Dissolution is the process where a solute integrates into a solvent to form a solution. Common examples include dissolving salt (NaClNaCl) or sugar (C12H22O11C_{12}H_{22}O_{11}) in water (H2OH_2O).

Temperature: Increasing the temperature increases the kinetic energy of the solvent molecules. This leads to more frequent collisions between the solvent and solute, increasing the rate of dissolution.

Surface Area (Particle Size): Smaller particles have a larger surface area per unit mass. For example, powdered sugar dissolves faster than a sugar cube because more solute molecules are exposed to the solvent (H2OH_2O) simultaneously.

Stirring (Agitation): Stirring moves the dissolved solute away from the surface of the solid, bringing fresh solvent into contact with the solute, thereby speeding up the process.

Saturated Solution: A solution in which no more solute can be dissolved at a specific temperature. The point of saturation depends on the nature of the solute and the temperature (TT).

Solubility: The maximum amount of solute that can be dissolved in 100extg100 ext{ g} of a solvent at a specified temperature.

📐Formulae

Mass of Solution=Mass of Solute+Mass of Solvent\text{Mass of Solution} = \text{Mass of Solute} + \text{Mass of Solvent}

Concentration (Mass/Mass %)=(Mass of SoluteMass of Solution)×100\text{Concentration (Mass/Mass \%)} = \left( \frac{\text{Mass of Solute}}{\text{Mass of Solution}} \right) \times 100

Concentration (Mass/Volume %)=(Mass of SoluteVolume of Solution)×100\text{Concentration (Mass/Volume \%)} = \left( \frac{\text{Mass of Solute}}{\text{Volume of Solution}} \right) \times 100

💡Examples

Problem 1:

A solution is prepared by dissolving 40extg40 ext{ g} of common salt (NaClNaCl) in 320extg320 ext{ g} of water (H2OH_2O). Calculate the concentration in terms of mass by mass percentage of the solution.

Solution:

Mass of solute=40extg\text{Mass of solute} = 40 ext{ g} Mass of solvent=320extg\text{Mass of solvent} = 320 ext{ g} Mass of solution=40extg+320extg=360extg\text{Mass of solution} = 40 ext{ g} + 320 ext{ g} = 360 ext{ g} Concentration=40360×100=11.1%\text{Concentration} = \frac{40}{360} \times 100 = 11.1\%

Explanation:

To find the concentration, we first find the total mass of the solution by adding the solute and solvent. Then, we apply the mass percentage formula.

Problem 2:

Why does a crystal of potassium permanganate (KMnO4KMnO_4) dissolve faster in hot water than in cold water?

Solution:

In hot water, the particles have higher Kinetic Energy (KE=12mv2KE = \frac{1}{2}mv^2).

Explanation:

At higher temperatures, solvent molecules move faster and collide with the KMnO4KMnO_4 crystals with more force and frequency, breaking the inter-particle forces of the solute more quickly.