Solutions & Concentration Terms (%w/w, %v/v, %w/v)
By Abhishek Sengar | CHEMCA – JEE & NEET Chemistry
Recommended Prerequisite
Before calculating mass percentages and molar masses of solutes, ensure your foundational Mole Concept basics are rock solid! Check out our comprehensive guide here: Some Basic Concepts of Chemistry for Class 11 and JEE/NEET.
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Lecture 8: Some Basic Concepts of Chemistry
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Hello students! Welcome to Lecture 8. After studying percentage purity and yield, we now step into the world of Solutions and Concentration Terms. This is a critical foundation for Physical Chemistry, especially for upcoming chapters like Solutions (Class 12) and Chemical Equilibrium.
1. What is a Solution?
A solution is defined as a homogeneous mixture of two or more components. The simplest solution, containing exactly two components, is called a Binary Solution.
Solute
Usually present in a lower amount. A solution can have more than one solute (e.g., salt + sugar mixed in water).
Solvent
Usually present in a higher amount. There is strictly only one solvent in a solution.
Golden Rule of Physical State:
The physical state of the final solution (Solid, Liquid, or Gas) is ALWAYS the same as the physical state of the Solvent.
The 9 Types of Solutions
Based on the physical states of the solute and solvent (Solid, Liquid, Gas), there are 9 possible combinations.
Special Note: A Gas dissolved in a Gas ALWAYS forms a True Solution.
2. Concentration Terms Introduction
Concentration terms explain the relationship between the mass, volume, or moles of the solute and the solvent/solution. We will study several terms including: %w/w, %v/v, %w/v, Molarity (M), Molality (m), Mole Fraction (χ), ppm, ppb, Normality (N), and Strength.
Mass of Solution = Mass of Solute + Mass of Solvent
3. Mass by Mass Percentage (% w/w)
% w/w = (Mass of Component / Total Mass of Solution) × 100
*Units of mass must be identical in numerator and denominator.
Trick Question: What is the mass % of NaOH if 40g NaOH is mixed with 160g water?
- Solute Mass = 40g. Solvent Mass (Water) = 160g.
- Common Mistake: 40 / 160 × 100 = 25%. (WRONG! 160g is not the solution).
- Correct Method: Solution Mass = 40 + 160 = 200g.
- % w/w = (40 / 200) × 100 = 20%.
4. Dilution Concept
Dilution is the process of adding solvent (like water) to an existing solution.
The core concept of dilution solving: When you add water, the concentration drops, but the total mass (or moles) of the Solute remains exactly the same!
Example Problem: Diluting H2SO4
What mass of water must be added to 500g of a 4% H2SO4 solution to reduce its concentration to 1%?
- Find mass of pure H2SO4 originally: 4% of 500g = 20g.
- In the new 1% solution, that same 20g of solute represents 1% of the new total mass.
- 1% = (20g / New Total Mass) × 100 → New Total Mass = 2000g.
- Water added = New Total Mass (2000g) - Old Total Mass (500g) = 1500g of Water.
5. Volume by Volume (% v/v) & Mass by Volume (% w/v)
Volume by Volume (% v/v)
%v/v = (Vol of Solute / Vol of Solution) × 100
Both units must be the same (e.g., mL and mL). Solved identically to mass percentage problems.
Mass by Volume (% w/v)
%w/v = [Mass of Solute (g) / Vol of Soln (mL)] × 100
Crucial Unit Rule: The solute MUST be in grams, and the solution volume MUST be in mL.
Test Your Understanding! 🎯
Take this 10-question MCQ quiz to verify your grasp of Lecture 8. Explanations and study recommendations will be revealed upon submission.
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