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Concentration of a Solution

Concentration tells how much solute is present in a given amount of solution or solvent.

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Student-friendly explanation

A concentrated solution has comparatively more solute, while a dilute solution has comparatively less solute. In Class 9 numerical questions, concentration is commonly expressed as mass percentage or volume percentage.

How to write this in exams

  1. 1

    Start with the exact idea

    Concentration tells how much solute is present in a given amount of solution or solvent.

  2. 2

    Then show how to use it

    Identify solute amount. Find total solution amount if not directly given. Choose mass or volume formula. Substitute carefully. Add percent sign.

  3. 3

    Add one concrete example

    If 10 g salt is dissolved to make 100 g solution, the mass percent of salt is 10%.

  4. 4

    Avoid this incomplete answer

    For 5 g sugar in 95 g water, writing 5/95 × 100 is wrong because 95 g is only solvent, not solution.

Definition

Concentration tells how much solute is present in a given amount of solution or solvent.

Example

If 10 g salt is dissolved to make 100 g solution, the mass percent of salt is 10%.

Rule to remember

Mass percent = (mass of solute / mass of solution) × 100. Volume percent = (volume of solute / volume of solution) × 100.

Memory hook

Percent concentration means part out of whole solution.

Examples and method

Worked example

A solution has 5 g sugar dissolved in 95 g water. Mass of solution = 5 g + 95 g = 100 g. Mass percent of sugar = 5/100 × 100 = 5%.

Method to apply

Identify solute amount. Find total solution amount if not directly given. Choose mass or volume formula. Substitute carefully. Add percent sign.

Diagram support

A labelled calculation box can show solute amount over total solution amount multiplied by 100.

How CBSE asks it

Questions usually provide solute and solvent quantities and ask for mass percent or volume percent concentration.

Avoid common mistakes

Common confusion

Students often divide by mass of solvent instead of mass of solution in mass percent questions.

Common wrong answer

For 5 g sugar in 95 g water, writing 5/95 × 100 is wrong because 95 g is only solvent, not solution.

Exam tip

Underline whether the question asks mass by mass percent or volume by volume percent before substituting values.

Quick check

Why is the denominator mass of solution in mass percent concentration?

The denominator is mass of solution because mass percent compares the mass of solute with the total mass of the final solution, not only with the solvent.

Answer writing and exam use

1-mark answer

Concentration tells how much solute is present in a given amount of solution or solvent.

2-mark answer

Concentration tells how much solute is present in a given amount of solution or solvent. Mass percent = (mass of solute / mass of solution) × 100. Volume percent = (volume of solute / volume of solution) × 100. If 10 g salt is dissolved to make 100 g solution, the mass percent of salt is 10%.

3-mark answer

A concentrated solution has comparatively more solute, while a dilute solution has comparatively less solute. In Class 9 numerical questions, concentration is commonly expressed as mass percentage or volume percentage. Mass percent = (mass of solute / mass of solution) × 100. Volume percent = (volume of solute / volume of solution) × 100. A solution has 5 g sugar dissolved in 95 g water. Mass of solution = 5 g + 95 g = 100 g. Mass percent of sugar = 5/100 × 100 = 5%. Questions usually provide solute and solvent quantities and ask for mass percent or volume percent concentration. For 5 g sugar in 95 g water, writing 5/95 × 100 is wrong because 95 g is only solvent, not solution.
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