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The Amazing World of Solutes, Solvents, and Solutions - Concentration of Solutions

Grade 8CBSE

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

🔑Concepts

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A solution is a homogeneous mixture of two or more substances. The component that dissolves the other substance is called the solvent, and the component being dissolved is the solute.

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Concentration of a solution is the amount of solute present in a given amount (mass or volume) of solution, or the amount of solute dissolved in a given mass or volume of solvent.

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A Saturated Solution is one in which no more solute can be dissolved at a specific temperature. The maximum amount of solute that can dissolve in 100 g100 \text{ g} of solvent at that temperature is called its solubility.

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An Unsaturated Solution is one where the amount of solute contained is less than the saturation level at that temperature.

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Concentration can be expressed in multiple ways, primarily Mass by Mass percentage and Mass by Volume percentage in Grade 8 Science.

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Common examples include a solution of sugar in water (C12H22O11C_{12}H_{22}O_{11} in H2OH_2O) and Tincture of Iodine (Iodine I2I_2 dissolved in alcohol).

📐Formulae

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

Mass by mass percentage of a solution=(Mass of soluteMass of solution)×100\text{Mass by mass percentage of a solution} = \left( \frac{\text{Mass of solute}}{\text{Mass of solution}} \right) \times 100

Mass by volume percentage of a solution=(Mass of soluteVolume of solution)×100\text{Mass by volume percentage of a solution} = \left( \frac{\text{Mass of solute}}{\text{Volume of solution}} \right) \times 100

Concentration=Amount of soluteAmount of solution\text{Concentration} = \frac{\text{Amount of solute}}{\text{Amount of solution}}

💡Examples

Problem 1:

A solution contains 40 g40 \text{ g} of common salt (NaClNaCl) in 320 g320 \text{ g} of water (H2OH_2O). Calculate the concentration in terms of mass by mass percentage of the solution.

Solution:

Mass of solute (NaClNaCl) = 40 g40 \text{ g}. Mass of solvent (H2OH_2O) = 320 g320 \text{ g}. Total mass of solution = 40 g+320 g=360 g40 \text{ g} + 320 \text{ g} = 360 \text{ g}. Concentration = (40360)×100=11.1%(\frac{40}{360}) \times 100 = 11.1\%.

Explanation:

To find the mass by mass percentage, we first determine the total mass of the solution by adding the solute and solvent. Then we divide the mass of the solute by this total mass and multiply by 100100.

Problem 2:

If 20 g20 \text{ g} of sugar is dissolved in enough water to make a 250 mL250 \text{ mL} solution, calculate the mass by volume percentage.

Solution:

Mass of solute = 20 g20 \text{ g}. Volume of solution = 250 mL250 \text{ mL}. Mass by volume percentage = (20 g250 mL)×100=8%(\frac{20 \text{ g}}{250 \text{ mL}}) \times 100 = 8\%.

Explanation:

Mass by volume percentage uses the mass of the solute (20 g20 \text{ g}) divided by the total final volume of the solution (250 mL250 \text{ mL}), expressed as a percentage.