Q.Match the terms given in Column I with expressions given in Column II.
Column I:

The key idea is to correctly identify the definitions of various concentration terms used to express the composition of solutions.

1. Mass percentage is defined as the mass of the solute component in solution divided by the total mass of the solution, multiplied by 100. This matches expression (d).
2. Volume percentage is defined as the volume of the solute component in solution divided by the total volume of the solution, multiplied by 100. This matches expression (c).
3. Mole fraction is defined as the number of moles of a component divided by the total number of moles of all components in the solution. This matches expression (b). …

Understanding the composition of a solution is fundamental in chemistry. Concentration terms provide a quantitative way to express the amount of solute dissolved in a given amount of solvent or solution. Each term serves a specific purpose, depending on whether we are interested in mass, volume, or moles, and whether the quantity is relative to the solvent or the total solution.

Let's break down each term and match it to its correct expression.

1. Mass percentage (w/w%)

   • Concept: Mass percentage expresses the mass of the solute as a percentage of the total mass of the solution. It is a ratio of masses, making it independent of temperature changes.
   • Formula:

     $\text{Mass percentage} = \frac{\text{Mass of solute}}{\text{Mass of solution}} \times 100$

   • Matching: This definition directly corresponds to expression (d) in Column II. (i) Mass percentage $\leftrightarrow$ (d) $\dfrac{\text{Mass of the solute component in solution}}{\text{Total mass of the solution}}\times 100$.

2. Volume percentage (v/v%)

   • Concept: Volume percentage expresses the volume of the solute as a percentage of the total volume of the solution. This measure is commonly used for liquid-liquid solutions. Since volumes are temperature-dependent, volume percentage also changes with temperature.
   • Formula:

     $\text{Volume percentage} = \frac{\text{Volume of solute}}{\text{Volume of solution}} \times 100$

   • Matching: This definition directly corresponds to expression (c) in Column II. (ii) Volume percentage $\leftrightarrow$ (c) $\dfrac{\text{Volume of the solute component in solution}}{\text{Total volume of solution}}\times 100$.

3. Mole fraction ($\chi$)

   • Concept: Mole fraction is a ratio of the number of moles of a particular component to the total number of moles of all components (solute and solvent) present in the solution. It is a dimensionless quantity and is independent of temperature. The sum of mole fractions of all components in a solution is always equal to 1.
   • Formula:

     $\text{Mole fraction of component A} = \frac{\text{Number of moles of component A}}{\text{Total number of moles of all components}}$

   • Matching: This definition directly corresponds to expression (b) in Column II. (iii) Mole fraction $\leftrightarrow$ (b) $\dfrac{\text{Number of moles of a component}}{\text{Total number of moles of all the components}}$.

4. Molality ($m$)

   • Concept: Molality is defined as the number of moles of solute dissolved per kilogram of solvent. It is a very useful concentration term because it involves masses (moles of solute and mass of solvent), making it independent of temperature.
   • Formula: …

Method: Definition Matching by Concept Analysis

Step 1: Recall the standard definition of each term in Column I.

• Mass percentage = $\dfrac{\text{Mass of solute}}{\text{Total mass of solution}} \times 100$
• Volume percentage = $\dfrac{\text{Volume of solute}}{\text{Total volume of solution}} \times 100$
• Mole fraction = $\dfrac{\text{Moles of a component}}{\text{Total moles of all components}}$
• Molality = $\dfrac{\text{Moles of solute}}{\text{Mass of solvent in kg}}$
• Molarity = $\dfrac{\text{Moles of solute}}{\text{Volume of solution in litres}}$

Step 2: Match each definition to the corresponding expression in Column II.

Here are the most common mistakes students make when matching concentration terms, along with how to avoid each.

1. Confusing Molarity and Molality (The Most Frequent Error)

• The Mistake: Students match Molarity (v) with option (e) and Molality (iv) with option (a). They see "moles" and "volume" and rush to connect them, forgetting the key difference in the denominator.
• Why it happens: Both terms involve "moles of solute," so the focus shifts to the denominator. Students often misread "volume of solution" vs. "mass of solvent."
• How to Avoid:
  • Memorise the denominator: Molarity = Volume of solution (litres). Molality = Mass of solvent (kg).
  • Use a mnemonic: "Molarity is about the total volume; Molality is about the solvent's mass."
  • Correct mapping: (v) Molarity → (a). (iv) Molality → (e).

2. Forgetting the "× 100" in Percentage Terms

• The Mistake: Students match Mass percentage (i) with an expression that lacks the multiplication by 100, or they match it with a simple ratio (like mole fraction).
• Why it happens: The word "percentage" is overlooked. Students see "mass of solute / mass of solution" and think it matches, ignoring that a percentage requires the factor of 100.
• How to Avoid:
  • Look for the "× 100": Any term ending in "percentage" must have a × 100 in its definition.
  • Correct mapping: (i) Mass percentage → (d). (ii) Volume percentage → (c).

3. Mixing Up Mole Fraction with Other Ratios

• The Mistake: Students match Mole fraction (iii) with option (a) or (e) because they see "moles" and stop reading carefully.
• Why it happens: Mole fraction is the only term that involves "total number of moles of all components." Students often miss the phrase "all components" and confuse it with a simple ratio.
• How to Avoid:
  • Spot the keyword "component": Option (b) says "a component" and "all the components." This is unique to mole fraction.
  • Correct mapping: (iii) Mole fraction → (b).

4. Ignoring the "Volume of Solute" vs. "Volume of Solution" in Volume Percentage …